Clean Fresh Air

Introduction

Fresh Air Beach

Updated May 8, 2019

After having just written Air Oasis and My Light Tube, I thought that now would be a good time to continue on with the theme of clean air by discussing what I do here in the woods of northern Wisconsin to keep the indoor air quality high. I’ve title this article Clean Fresh Air because where I live, the mold counts can get quite high outdoors especially in late fall. So although fresh air is good in general, I make a point of “cleaning” the fresh air that enters our home as a way of reducing the biotoxin load on my body.

Now you may have read that Dr. Shoemaker has said that outdoor molds don’t produce biotoxins at nearly the same level as when they’re growing unfettered inside a wet building. Inside, protected from the elements, and with limited competition from the cadre of bacteria and fungi that live outside, indoor molds feeding off abundant food sources have the additional resources needed to create all kinds of nasty biotoxins. That doesn’t mean that outdoor molds and bacteria feeding off of rotting materials don’t produce biotoxins too. It’s just at much lower levels.

In support of the contention that there is always some degree of nasty biotoxins in the outdoor air, you can read my experience with Decks, Gazebos, Porches, Stoops & Mold. Also, taking the advice of Lisa Petrison and Erik Johnson, many “mold avoiders” have gotten significantly better by simply moving to pristine, mold-free environments. Additionally, Erik Johnson has recounted in Dr. Shoemaker’s book how he’d take mold hits while hang gliding. In other words, some outdoor air can be problematic for those with Chronic Inflammatory Response Syndrome (CIRS).

For the remainder of this article, I’m going to discuss what I do to minimize the biotoxins in our indoor air. Some of these strategies I’ve already discussed elsewhere and will only make brief mention of here. Others I’m mentioning here for the first time.

Letting In Fresh Air

Fresh Air Clouds

To begin, I want to point out that it’s really important to bring in lots of fresh air into your house on a daily basis. Andrea Fabry in Open a Window, Even in the Winter, does a nice job discussing the importance of letting in fresh air. Odors from cooking, cleaning, VOCs from furniture and building materials, and so on build up to unhealthy levels in poorly ventilated homes. Regardless of whether a person has CIRS or not, it’s important to let in lots of fresh air on a daily basis.

If you’re curious to know just how much ventilation is recommended, you could purchase a copy of ASHRAE 62.2 “Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings”. Alternatively, Ventilate Right and Working Through ASHRAE 62.2 discuss this standard. The formula for calculating the continuous air exchanges in a home is based upon the total square footage of the home and the number of bedrooms. In addition to continuous ventilation, ASHRAE also recommends using a 100 cfm kitchen fan and a 50cfm bathroom fan intermittently.

Continuous Air Flow in CFM = (Total Square Footage/100) + (Number of Bedrooms X 7.5)

As an example, in a 2,000 square foot home with two bedrooms, the amount of fresh air to be brought into the home 24 hours of the day is 10+15= 25 cubic-feet-per-minute (cfm). For older homes that generally leak somewhere between 40-60% of their volume per hour through gaps and cracks, ASHRAE minimum standards for continuous ventilation are often met without the addition of a fan. In our example home with 8-foot tall ceilings and a 40% leakage rate, the home is already exchanging (16,000X0.4)/60= 107cfm through leakage. On the other hand, if our example home was newer with 5% leakage, only (16,000X0.05)/60= 13cfm would be exchanged continuously due to leakage. As such, the newer home would require the addition of a small, continuously running fan.

Note: It’s important to realize that this is a minimum standard. In many cases, you’ll want to exceed this standard.

Equipment to bring in fresh outside air can be as simple as wiring a bath fan to exhaust indoor air whenever the furnace/AC blower is running along with installing a duct to the outside for fresh make-up air to enter the building. Of course the fan would be sized larger to account for the fact that it runs intermittently. Alternatively, more sophisticated Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV) not only bring in fresh air but keep energy bills lower. Through the use of a mini radiator of sorts, they recover heat from the outgoing air in cold winters and the cold from air-conditioned air exiting the building in summer.

HRV HRV Open HRV Inside
HRV Fan Dirt HRV Core Dirt Fresh Air Inline Filter

HRV – Dirt Buildup – Inlet Air Filter

In HRV/ERV & Filtered Fresh Air, I discuss the importance of cleaning HRV/ERV units on a yearly basis. These units are common sources of mold. In addition, the ductwork that brings in fresh outdoor air is also commonly moldy. This isn’t too surprising given the dust and dirt in the incoming “fresh” air in combination with damp outdoor conditions, or conditions that produce condensate within the HRV/ERV. I clean our HRV and fresh air ducting on a yearly basis and have installed a pleated filter within the fresh air ducting.

Dehumidifier Whole House

At this point I should note that I only run the HRV in the winter. In the summer, I bring in fresh air daily using pleated window filters and a whole house attic fan. To keep the relative humidity levels under 45% inside, I run a whole house dehumidifier that is connected to the same ductwork as the HRV. It’s just a matter of switching a couple of dampers and I’m ready for the upcoming season. Note: The yellow ropes and pulley make it easy to drop the unit down for yearly cleaning.

Central Air Conditioning

Central Air Conditioning

Where I live, air conditioners are often moldy. If you think about it, you have warmer indoor air rushing over a much cooler surface. We all know what happens when warm air comes in contact with a cooler surface. It’s just like a glass of cold lemonade sitting outside on a summer day. Water vapor in the air condenses on the outer surface of the glass and drips down the side. If you’re interested, you can read more about relative humidity in Cooler Air is More Humid.

Air conditioner design always includes some way for the water dripping off the very cold evaporator coils to escape. They do this by placing a pan underneath the coils that collects the water and directs it out of the unit. In the case of whole house air conditioners, the water in the drip pan runs out what’s called a “condensate line”. This hose runs from inside the ductwork above the furnace where the A/C coils sit and runs to the floor drain. In the case of window units, the water in the pan simply drips to the ground outside through one or more holes on the bottom of the machine.

Add to this dripping water the fact that the air rushing past the cold coils contains dust and dirt. Compared to window units, the air rushing past the cold coils in a whole house air conditioner is much cleaner as it generally has just passed through the furnace filter. If you have a pleated furnace filter with a MERV 11 rating or higher that you replace often, this air will be pretty clean (Filtrete is a good brand). In comparison, the cold coils on window units use a very thin plastic filter that is really only for catching the big stuff. Consequently, it should be removed and washed with mild detergent every few weeks. It’s very important to keep these air filters clean.

Central AC Coil

Happily, all that dripping condensate does have some “washing” action that tends to keep the pan and coils clean. Nonetheless, with all that moisture around, it is possible for mold to get established on the coils themselves or in the drip pan. I visually inspect, and clean all our A/C coils on a yearly basis. As a matter or course, I’ll flush the surfaces with a water containing QUAT and then rinse with clean water. In addition, I’ll visually inspect the condensate line and replace it if it shows any sign of “grunge” building up inside.

What’s insane is that typically there is very limited or no access to whole house A/C coils. When the house is built, the coil is set on top of the furnace and metal ductwork is formed up around the coils sealing them inside. If you’re lucky, you’ll have a smallish access panel that can be removed. If not, you can cut your own large access hole using a pair of tin snips. Squares of sheet-metal to be used as a cover and screws are readily available at any big box hardware store to close up the hole after inspection.

Central AC Coil Closeup

Using a bright flashlight and a mirror on a stick, you can usually do a pretty good job of looking over the surfaces of the coils and pan. Really take your time peering through the thick coils themselves to make sure nothing is growing deep inside on the fins. This is a job you should do when you have some time as you really want to convince yourself that the aluminum fins that make up the coil are shiny bright clean everywhere. Note: In the picture to the right, I cultured the patch of mold at the top of the A-frame and found out it was stachybotrys.

Depending on the configuration, mold will tend to grow in one place or another and may be tucked away at the back of the unit so make sure to visually inspect well. Anything less than shiny bright aluminum means cleaning is required. If mold is found and you have CIRS, you’ll need to develop a protocol for cleaning not only the coils, but the ductwork and the entire house – see A/C Coil & Blower Cleaning.

Central Evaporative (Swamp) Coolers

Swamp Cooler Diagram

Evaporative coolers, also called “swamp coolers”, are an alternative form of air conditioning and are a recipe for mold. These devices work by passing volumes of warm outside air over a wetted surface. Some of the water that the air passes over evaporates thereby cooling the air. This cooler and moister air is then blown inside the house through the ductwork.

Swamp coolers can only work where the outside air is dry and hot. Air that has passed over the wetted evaporator pad has a much higher relative humidity. You can only get away with this in really arid climates. Anywhere else and you’re going to end up having water condensing inside the ductwork and the building.

So what’s the problem if you live in a really dry climate? To answer this, take a look at my discussion of humidifiers. Swamp coolers suffer from the same design flaws. Basically, you have a large pool of water and wetted surfaces inside an enclosure with all sorts of dirt and debris that builds up inside. Warm air, water, and the organic matter is a perfect recipe for serious mold growth.

Swamp Cooler Dirty

There is a reason they call them swamp coolers. Owners know when they haven’t been keeping up with maintenance because the mold growth gets so bad that the inside of their homes start to smell like a swamp! Given that swamp coolers are often mounted on the roof, it’s not surprising that most are poorly maintained. For someone with CIRS, you should avoid swamp coolers like the plague.

UV Light Air Purification

As discussed in UV Light Studies, UV-C light can really help improve indoor air quality by keeping the A/C coils clean. In Air Oasis Limitations, I discuss the importance of making sure the coils are mold free before installing a UV-C light next to the coils. If the coils are moldy and you install a UV-C light, the light will start killing the mold in mass within minutes liberating large amounts of toxins in the air.

I believe people that complain of poor air quality after installing a lamp suffer from this effect. I don’t think ill health effects are due to pathogens being killed in the air or some other chemical reaction. If you run the math, the fraction of one second pathogens in the air come within killing range of these very weak UV-C lights isn’t enough to really knock out anything. The real benefit from UV-C lights is having them constantly shining on the A/C coils at low levels.

Update November 1, 2016

In the 2016 Third Annual Conference, Certified Indoor Environmental Consultant (CIEC) Larry Schwartz, commented that some clients that installed UV-C lights above their AC coils suffered from respiratory issues even in homes that were mold free. He speculated that ozone produced by the lamp was building up in the rooms to levels that were damaging to the lungs of the occupants.

In fact, the germicidal UV-C lamps sold to be used above AC coils block the 185nm wavelengths. It is the 185nm long waves that turns oxygen in the air into ozone. They block this wavelength by using sodium-barium glass tubing or by coating quartz tubing. Of course, some 185nm waves get out but the level of ozone production by germicidal lamps is very small.

To give you an example, compared to lamps used above AC coils, my Light Tube uses a very high powered UV-C germicidal lamp. I’m quite familiar with the smell of ozone and never detected even the slightest whiff of ozone. To give you a sense of the levels we are talking about, people can smell ozone at concentrations as low as 0.01ppm. OSHA sets a limit of 0.05ppm for a 24 hour exposure. Electric motors, copy machines, and the like produce ozone but are considered safe when the level is below 0.04ppm.

In comparison, I was really surprised at how much ozone is produced by my 3000G3 Air Oasis. The lamp in this machine does not block the 185nm wavelength. Even if I run a ceiling fan, there is a strong ozone smell on the lower level of our house after a few hours of use. That floor doesn’t have any fabric furniture, carpeting, wood flooring, and the like for the ozone to immediately react too.

Add to this the fact that the half-life of ozone isn’t very long. Granted the half-life of ozone all by itself is 3 days at room temperature. However, in a room filled with furniture and dust floating in the air, the half-life is probably around 10 minutes at best.

So the germicidal lamp produces some minuscule amount of ozone. After 30 minutes, whatever amount was produced has reacted so there is only about 10% left. In total, maybe you get a two fold increase in the tiny amount produced by the lamp. You can see why I don’t think its ozone buildup that’s causing problems for these folks. Personally, instead of having the UV-C lamp running continuously, I’d wire it to a timer set to run the lamp 3-4 hours daily. This would prolong the bulb life while still knocking out any potential buildup on the coils.

So what may be the source of lung irritation? UV-C light does degrade plastic and rubber. If these parts are near the lamp, chemicals will be produced. Alternatively, maybe the film of oil on new ductwork is being degraded. Then again, I’ve read that even when manufacturers do put UV inhibitors in plastic, they only protect against UV-B as UV-C is blocked by the earth’s atmosphere. Finally, I bet there are cheaper lamps that don’t do as good of a job blocking the ozone producing 185nm waves.

Clearly a lot of people use UV-C lamps without issue. For a gas that has incredible healing qualities, ozone sure does get demonized a lot. Look honey, it’s ozone! Grab the kids and run 😉

End Update

Having said this, it is possible in some A/C units that the UV-C light is reacting with plastic drip pans or rubber parts nearby. Before installing a lamp, call the manufacturer and make sure the plastic drip pan won’t be destroyed by the light. The pans of newer units typically have UV inhibitors in the plastic for just this reason. If there are any other rubber or plastic parts nearby, use aluminum faced ductwork tape and cover over these UV-C sensitive parts to protect them.

While we’re on the topic of UV-C light, I thought I’d take a minute to talk about the on-the-fly UV-C light I’ve installed in our home. On-the-fly means that I’m running a UV-C lamp powerful enough to knock out many of the pathogens in the air as they rush past the lamp installed inside our ductwork. This is different than when a small UV lamp constantly shines on the A/C coils. We know UV-C light shining on the coils keeps them clean but killing pathogens in the fraction of a second it takes for air inside ductwork to rush past a lamp is a whole other matter. By understanding a bit about my installation, you’ll then be able to better see why I have my doubts when it comes to commercially available on-the-fly UV units for homes.

UV House End Cap UV House Lamp UV House Lamp Closeup
UV House Tube UV House Tube Closeup UV House Core Component Relay

In our home, we run a localized air conditioner called a mini-split along with using hot-water heat in winter. As a result, our home doesn’t have lots of ductwork like most homes do. Instead, we use small 5” diameter ducting connected to both an HRV and a whole house dehumidifier. In winter, we use the HRV to bring in fresh air. In the summer, we use a whole house fan and pleated window filters to let fresh air in during a few hours each morning. Given that the warmer summer air holds more moisture, we’ll run the dehumidifier whenever the relative humidity gets above 45 percent inside.

After doing some research and convincing myself that I could get a good kill rate, I decided to install a powerful 5-foot long UV-C lamp within our small diameter ductwork. To do this we cut out a portion of the ceiling so we could remove the galvanized steel ducting and replace it with highly reflective mirror polished aluminum. The powerful long lamp in combination with slower HRV air speeds and small diameter shiny bright duct produces a killing power of about 30,000 uW-sec/cm^2 (micro-watt seconds per square centimeter).

For those more technically minded, I used a Core Components CVR21C-0 relay to turn on the UV lamp whenever either the dehumidifier or HRV are running. I’m using a GPHHVA1554T6L ozone free UV-C lamp that produces 750 uW/cm^2 at a distance of one meter. The lamp is driven by a Workhorse 7 ballast. Initially, I worked with the nice folks over at American Air & Water to help me begin to understand how to calculate energy output. I purchased hardware from them initially before branching out and designing my own UV Light Tube along with sourcing materials.

In addition to using mirror polished aluminum, I also installed a tee in the ductwork and fitted one end of the tee with an end-cap. Removing the end-cap allows me to get at the lamp so I can replace it every two years. It also allows me to use a duster taped to a long stick in order to keep the lamp and mirror polished aluminum dust free. Dust build up will significantly lower the killing energy.

Getting back to the 30,000 uW-sec/cm^2 energy output of my configuration and looking over the UV Kill Charts, you’ll see that at this level bacteria and viruses are toast. The lamp will also neutralize many molds, although some amount of tougher strains of Aspergillus and Penicillium will get by unscathed. Given that we live in woods and after reading the Sanuvox study, I opted for this extra level of air purification.

So let’s now look at commercially available on-the-fly units. For example, Sanuvox makes UV-C air purifiers installed in conventional ductwork such as the R4000GX. These units only treat a portion of the air rushing through the ductwork. In addition, fixed blades at the upstream end of the unit limit the speed of the air that does pass through the device. This makes sense as you need to slow down the air so pathogens are exposed to the light long enough to kill them.

Sanuvox R Plus

However, when I run the math on a more powerful unit like the R4000GX, the energy output is really low. Specifically, using a typical 1,200 cubic-feet-per-minute (cfm) furnace blower and 16”x18” main trunk, the flow through the trunk is [1,200/(16×18/144)]= 600 feet-per-minute (fpm). Given that the end of the Sanuvox unit is blocked off by the fixed fins, let’s generously assume the flow through the Sanuvox unit is 1/3rd of what it is inside the main trunk. This equates to (600/3)= 200 fpm or 3.3 feet-per-second (fps). (Note: Literature sites typical flow rates of 400 and 500 fpm so we’re being generous in our energy output calculations in using 200 fpm.)

Given that the lamp is 10.5” long in a R4000GX, the contact time works out to be (10.5/12)/3.3= 0.27 seconds. Knowing that it only takes the air a little more than one-quarter of a second to rush past the lamp along with a stated power of 16,479 uW/cm^2 for the R4000GX, the energy output works out to be (16,479×0.27)= 4,450 uW-s/cm^2. If you go back and look at the UV Kill Charts, you’ll see that 4,450 uW-s/cm^2 isn’t that much.

The bottom line is that UV-C light shining on A/C coils helps keep the air cleaner due to the long contact time on the coils. However, with the numbers just stated, you can now see why I don’t think commercial on-the-fly units for homes do much. Note: If you’re interested, you can read more about on-the-fly UV air purification in My Light Tube.

Mini-Split Air Conditioner

Mini-Split Overview

For smaller spaces, hotels, and homes with unconventional designs, “mini-split” air conditioners are frequently used. The systems consist of an indoor evaporative unit that absorbs heat thereby cooling the air and an outdoor condenser that releases this heat outside of the building. Unlike conventional whole house systems that are installed inside large ductwork, mini-splits don’t require any ductwork. The indoor unit of a mini-split simply blows cold air into room that is installed in. It is like a window air conditioner except that it is mounted high up on a wall out of the way.

Just like any air conditioner, the evaporator coils in the unit inside get cold. When the warm indoor air is blown over these cold coils with a barrel fan, condensate collects and then drips through the coils. This condensed water then runs out a condensate line to the outside. As we know, when water and dirt are present, mold has a chance to grow so its important to regular clean these units.

Mini-Split Mold

We run a mini-split in our unconventionally designed home to cool the main floor space. As this article describes, I keep the air clean using window filters, an IQAir, and by regularly cleaning the dehumidifiers and air conditioners. As a consequence, I’ve never seen any buildup on the coils in any of our air conditioners and dehumidifiers including the mini-split. However, it doesn’t take but a minute looking on the Internet to realize the indoor unit of mini-splits can harbor serious mold growth. Below is a video of a moldy mini-split being cleaned without any thought for the biotoxins that are being blasted everywhere.


It May be Clean but Biotoxins Are Blown Everywhere

To keep our mini-split mold free, I wash the thin plastic filters with mild soap and water every month. Once I forgot about them for a couple of months and was surprised that I could smell a very slight “swampy” odor when I turned the machine on. Initially, I thought the coils were getting mold on them even though I wasn’t experiencing any symptoms. Upon inspection, the unit looked perfectly clean. Unsure of the source of the odor, I washed the thin filters. This resolved the matter so the thin layer of dust buildup on the filter must have been enough to trigger my sensitized sense of smell.

Given that we only run our mini-split a few months during the year, I clean it once at the end of every season. For others that are running their mini-split year round, I think it’s prudent to do two or more cleanings. Cleaning frequency should increase with more humid the air, dirtier air, and increased use. Initially clueless, I ran our mini-split for two years without cleaning and it developed serious buildup on the fan barrel cage that blows the air. This was enough to cause symptoms and got me going down the road of learning about the importance of cleaning all evaporative cooling devices on a regular basis.

To clean any air conditioner or dehumidifier, you have to disassemble it enough to get good access to the coils and the fan blades. This is important not only because you won’t be able to clean them well otherwise but also because you need to be able to visually see that they’re clean. By the way, they sell cans of chemicals you can spray up into mini-splits that wash out loosened debris. However, these chemicals have a serious smell to them and there is absolutely no way they clean out all the nooks and crannies – no way.

Unlike the video above wherein volumes of water are sprayed over the indoor unit and captured in a specially designed basin affixed below, if you clean your equipment often, you can forgo all of this fuss because there won’t be any significant build-up. For myself, I use a hand-held pump-up spray that I fill with a water-quat solution. Using the sprayer, I rinse the aluminum coils with the solution. If I’m careful not to apply excess liquid, the solution runs down the coils and into the machine’s built-in drip pan then outside through the condensate line. I make the stream of liquid thick enough, and pump up just enough pressure, to make sure I’m sending the solution through the depth of the coils. After sitting for 10 minutes, I follow up with a clean water rinse. It’s easy-peasy.

What I’ve struggled to find a good solution for is the round, tubular shaped fan assembly. This assembly is called a barrel cage fan. The fins of the fan are very tightly spaced, hard to get at even after removing the outer hardware, and are curved. I’ve tried everything from soaking them with quat, small brushes, and a steam cleaner. Given the high speed, the dirt gets really packed onto the faces of fins. In the corners, it’s super hard to remove this dirt.

Mini Split UV

Given this pesky dirt along with having learned about the effectiveness of keeping A/C coils clean by shining UV-C light on them, I’ve decided I’m going to install tiny UV-C lamps inside my mini-split when I clean it this fall. The two small lamps shine primarily on the barrel fan and lower portion of the coils. Given the light color interior, some light will also be reflected deep into the machine. With the longer exposure times, I’m convinced it will keep the coils clean and hopefully help with build-up on the barrel fan too.

If you follow the installation directions, the UV lamps are meant to run continuously. I plan on installing a switch wherein I can turn the lamps off when the mini-split isn’t running. If you read about the energy required to knock out mold, this exposure time will be more than enough. In so doing, I’ll extend the lamp life slightly (although turning the lamps on and off does shorten their life). Also, even though I’m sure the mini-split plastic has UV inhibitors in it, I want to limit plastic exposure to UV light.

There are numerous videos online showing how to remove the outer coverings on a mini-split. Any patient person with a screwdriver and a bit of mechanical aptitude can accomplish the task. Here’s what I do on my machine.

Mini Split Mini Split Cover Off Mini Split Filters
Mini Split Electrostatic Filters Mini Split Cover Mini Split Wiring
Mini Split Air Diverter Mini Split Fan Guard Mini Split Barrel Fan
  1. Turn off the breaker. My mini-split uses 240 volt wiring so I’m extra careful.
  2. Lift off the front cover panel. There are no screws; just finagle the cover out of its slot.
  3. Remove the thin plastic air filter.
  4. Remove the outer shell covering. On my machine, there are three screws on the bottom. Gently lift and rotate the bottom edge of the outer cover upward so you can unplug the electrical connectors and then remove the cover completely. To prevent bending the delicate aluminum coil fins, this is best done with two people. To make sure you get the cover back in place upon re-assembly, notice the number and action of the plastic clips along the top edge.
  5. Remove the electrostatic cleaner (if present). Unscrew the screws, disconnect the wires, and unclip the thin plastic electrical grids from the coils.
  6. To get enough access to clean the barrel fan, remove the air diverter assembly in front of the fan. On my machine, this means first flexing the long plastic diverter that sweeps up and down so that it releases from its sockets. Next, I need to remove a plastic trim piece held in place with screws that in turn holds a metal mesh in place. Finally, I have to carefully unclip a series of plastic fins that oscillate side-to-side. It just takes a little patience and finesse.
  7. Place a plastic bag over the electronics at one end. I’m really careful to direct the stream of liquid onto the coils only so this is just in case I accidentally mess up and spray liquid where I shouldn’t.

Window Air Conditioners & Dehumidifiers

Window AC Filter

As with any device that compresses and then expands a refrigerant to create cooling, the evaporative coils on window air conditioners and dehumidifiers get wet with condensation. As noted previously, over time dirt can build up on the fins of these coils that together with the water create the conditions for mold. The tendency for mold growth depends on the humidity, cleanliness of the air passing through the machine, amount of use, and the like. Thankfully, there is some rinsing action as condensation trickles down through the cool fins and along the drip pan that tends to prevent dirt build up and consequently mold growth. For more details, you may want to read the Central Air Conditioners section above.

Nevertheless, for those with CIRS, it makes sense to regularly clean these condensation filled machines. Here in the woods of Wisconsin, I clean our window air conditioners twice during the 6 months they’re used during the year and the dehumidifiers once. For the window air conditioners, I flush out the outer coils and fan while they’re still in place half way through the summer. When fall arrives, I take our two window air conditioners and two dehumidifiers outside and thoroughly clean them.

Window AC Fan Dirt

It’s always surprising for me to see how much “lint” and gunk can build up on the outer half of window air conditioners in just three months. The fact that we have cotton wood trees in our area that release what looks much like small tuffs of cotton in spring doesn’t help. Often, I’ll see the beginning of a slight tint of reddish mildew starting to get a foothold in portions of the bottom of the machine that serves as the drip tray.

Given that we get a fair amount of rain, I’m always concerned that this buildup of organic matter in the outer half of the air conditioner will start to badly mold. The fact that the condenser coil in this outer half gets hot when the unit is running helps to dry out the machine. However, when it’s raining for days and the air conditioner is off, mold can start to get a foothold.

I don’t worry too much because this is outdoor mold that we know typically doesn’t produce toxins like the ones that grow inside water damaged homes. Also, there is a rigid foam wall between the outer and inner portions of the unit. It’s hardly air tight especially with one fan blowing cold air into the room and another hot air outside. Still, from my experience, it’s enough.

To stay on the safe side, about half way through our six month air conditioning season, I mix up a hand pump spray bottle with QUAT and water. I spray the outer coil that looks like a small radiator along with the outside fan, compressor, and drip tray below. I squirt the solution through the many slots on the sides and top of the machine.

I’m not worried about getting any of these parts wet because they’re built to be outside in the weather. After ten minutes of soaking, I follow up with a garden hose fitted with a nozzle. I’m careful not to use too much pressure that will bend the delicate aluminum fins while thoroughly flushing out all the debris. If I do accidentally bend some fins, I’ll follow up with a fin straightening tool.

At the end of the year, I take our window air conditioners and dehumidifiers outside for a good cleaning. The procedure is essentially the same only this time I remove the outer shells so that I can clean not only the outer coil, fan, and drip tray but the inner coil, fan, and tray. This is important because it’s the inner evaporator coil that gets wet with condensate. Given the whimsical thin plastic filter, these wet coils tend to get a build up of dirt on them over time. With regular cleaning, I’ve never had a problem with mold growth.

Window AC Coil Dirt Window AC Coil Dirt Closeup Window AC Drip Pan Dirt

On the other hand, when my wife and I traveled to the Mohave Desert a while back, we stayed at a quaint airbnb. Compared to typical roadside hotels, this little airbnb cottage was tucked away from all the commotion and was free from all the toxic chemicals found in the typical hotel that uses cleaning solutions and air fresheners. Unfortunately, after a couple hours of running the window air conditioner, I started feeling anxious. Minutes later and I had the inner plastic covering on the unit removed so I could see the evaporator fins. You guessed it; the fins were plugged with debris in spite of the fact that the flimsy plastic filter had been recently cleaned.

I took a tape sample home with me and viewing it under the microscope confirmed mold. Later, I informed the owners and gave them directions on how to safely clean the machine. I have no doubt this was done. They were very generous and caring. All in all, I like airbnbs over regular hotels.

Window AC Covers Window AC Coils & Fans Window AC Cleaning
Dehumidifier Dehumidifier Covers Dehumidifier Back

Getting back to cleaning air conditioners and dehumidifiers, it’s a relatively simple matter to remove the small number of screws that holds the outer shell onto these units. In order to get all the screws back where they belong, I’m careful to make note of any screw(s) that are different than the rest. I don’t want to put a long screw into a hole that is meant for a short one and potentially damage parts inside.

Generally, the covers lift right off. Sometimes there are plastic tabs that require gently prying the cover outward. For dehumidifiers with front and back covers, sometimes one or the other must be removed first. With the covers off, I place a rag or plastic bag over the electronics to protect them from water.

As usual, I use a mixture of QUAT and water in a spray bottle that I allow to soak for 10 minutes before using a garden hose. I’m careful to avoid spraying the protected electronics directly. For window air conditioners, it takes at least 15 minutes of spraying water in all directions to get the unit clean. Dehumidifiers don’t get dirt build up so it’s a quick rinse and they’re done.

The final step before re-assembly is to blow off all the parts with compressed air. Alternatively, you could let the units sit out in the sun to dry off while you take a break. If you inadvertently got the electronics wet, you want to make sure the machine is completely dry before plugging it back in. Once cleaned, I store the machines in a clean dry place until the following year.

Update May 8, 2019

Portable Air-Conditioners

Portable AC

When it comes to portable air-conditioners, I have my reservations particularly when it comes to the two-hose models. To understand why, we need to first look at how these units work. Understanding how the units work, we can predict where problems will arise.

To begin, portable air conditioners are units that can be placed anywhere in a room and moved about. Either one or two flexible hoses attach to the unit and are directed out a nearby window. A drip tray collects water that must be emptied regularly.

On one-hose units, room air is drawn into the unit with some portion passing over the cold evaporator coil wherein it is cooled and expelled back into the room. The remaining portion of room air that is drawn in passes over the hot condenser coil wherein it is heated. This heated air is exhausted out a nearby window via the single hose.

Dual hose units work essentially the same as single hose units except for the fact that the air that is blown over the hot condenser coil comes from a second hose that connects to outside air via a nearby window – not from the indoor air. This eliminates the “negative” air pressure issue with single-hose units and makes two-hose units more efficient.

To elaborate, on single-hose units, some of the indoor air is being exhausted outside and this creates “negative” air pressure in the room. In other words, air is pulled into the room from under doors and elsewhere to make up for the air that the unit it exhausting out the window. This air is invariably warmer and consequently, makes single-hose units less efficient. Portable Air Conditioner Operation

Both dual and single-hose units have drip trays. In window air-conditioners, the moisture that condenses on the cold evaporator simply drains to the outside. This is because half of the unit is outside of the building. In portable air-conditioners, this clearly isn’t possible because the entire unit sits in the room. As such, the moisture that condenses on the cold evaporator coil is collected in a reservoir that must be emptied on a regular basis.

Now that we understand how the units work, let’s look at why I have reservations about portable air-conditioners. Let’s start with the filters. All of the air drawn into the machine needs to be filtered to prevent excessive buildup on the coils – especially since these units sit near the floor where the air is dustier. From the brief review I made of various designs, it does not appear that this is always the case. If you decide to use one of these units, make sure that all in-coming air is filtered and that you clean the filters frequently.

When it comes to two-hose units, the outside air pulled in by the unit is not filtered. As a consequence, I can assure you this means you’ll have considerable buildup on the hot evaporator coil. This isn’t necessarily problematic as this coil is hot and does not get wet. However, full containment of any nastiness drawn in from outside relies on how well the unit is sealed and this is minimal. Granted, window units also collect “gunk” on their condenser coil but the coil sits outside and the airflow does not lend itself to leakage into the room like portable units. In contrast, the indoor air that passes over the condenser on single-hose units is filtered resulting in less buildup.

Taking a look at the hoses, I can tell you from experience that all the ribbing in those flexible hoses is going to collect debris. If it’s humid outside and you’re using a two-hose unit, the in-coming humid air will pass over and dampen this dirt on its way to the unit. If it’s raining outside, conditions are even worse with water that splashes on the window sill potentially being drawn into the intake. Even if the unit is off, humid air will still enter into a portion of the hose(s) closest to the window. This is a recipe for mold.

From this perspective, even though single-hose units are less efficient, their design makes them less prone to becoming moldy. All intake air is filtered. The exhaust air is hotter and drier making the likelihood of mold developing in the exhaust hose minimal. After all, think about all the hot, moist air in lint-laden dryer hoses. The heat along with the fact that they exhaust outside keeps them from being a problem.

So all in all, I worry about good filtration and the flexible hoses, particularly on dual hose units. If I couldn’t install a window unit, I would definitely get a single-hose unit with good filters. Personally, I wouldn’t touch a dual hose unit. And finally, just like with dehumidifiers and window units, I would pull off the covers and clean the coils along with the hose(s) on a yearly basis.

Update End

Whole House Ventilation & Window Filters

Window Filter In Use

In Sleep Sanctuary, I mentioned that I used MERV 11 pleated filter fabric to filter incoming fresh air. Here in northern Wisconsin, it’s surprising how dirty the replaceable filter material gets in one season. I’ve done spore traps in fall when they’re taking corn off the fields and the fusarium counts go way up. I don’t feel as well during these times.

Once I decided that I was going to filter all incoming air, I made up wooden frames and installed a whole house attic fan. The wooden frames are more durable than the cardboard framed filters I was originally using as seen in Sleep Sanctuary. Also, by using 1/8”x1” aluminum flat stock held on with screws, I can replace the filter material easily. This is a savings because I now buy a large roll of pleated filter material that I cut to size instead of buying pre-made, cardboard framed filters.

Note: In the picture to the right below the use of a filler strip. When the window is open, and the filter is in place, there is still a gap between the glass and the window frame. To fill this gap, I cut 1″ wide strips of wood just the right thickness and length and painted them white. I press fit the strips in place and leave them there during the summer; the strips look like part of the window frame. Without a filler strip, a lot of unfiltered air would enter the building.

Window Filter Dirt Window Filters Window Filter Filler

It’s important to install the filter material with a lot of pleats. The more pleats, the larger the overall area of filter material and the less air resistance. Mistakenly, I installed the filter material tight the first time. Even with a powerful whole house fan, there was very little incoming air through the filters. If this wasn’t bad enough, this situation creates a negative pressure (vacuum) in the house that can cause flue gasses from hot water heaters and the like to downdraft into the house. This is not good at all.

Window Filter Carcoal

I also experimented with window filters that not only had pleated filter fabric but also a layer of carbon. I purchased course carbon granules and poured them between two window screens that were one inch apart. Unfortunately, the combination of pleated fabric and a one inch carbon layer made the assembly virtually un-breathable. I was sort of surprised how much that layer of carbon reduced air flow. Consequently, the carbon idea got tossed.

Currently, I’ve got a total of 16 square-feet of 1” deep pleated MERV 11 filter fabric to let in air for a 1,000 cubic-foot-per-minute power attic fan. I’ve got window filters on every level. The fabric is installed with 15 pleats per foot. I buy rolls of 25” wide fabric with 525 pleats.

The current configuration lets in plenty of fresh air. However, I’m not convinced there is enough filter area. As such, I’m planning on increasing the number of pleats or increasing the pleat depth to 2-inches for next year.

Younit MERV 11 Rolls
All Filters MERV 8 Rolls

Whole House Fan Whole House Fan Removal Whole House Fan Door
Whole House Fan Pulley Whole House Door Cord Whole House Fan Plate

In the pictures above, you can see that I’ve mounted the attic fan to a 1/2″ piece of plywood that rests on two wood cleats on opposite sides of the attic access hole. Should I need to get up in the attic, it’s a simple matter to rotate the plywood mounted fan out of the opening. I also wired an outlet right next to the fan that is connected to a switch with a timer. Note: Given that I’m operating the fan as needed, I by-passed the thermostat wiring that comes with the fan.

When it comes time to run the fan, I pull the 1/4″ nylon cord that’s attached to a cover over the attic access hole. The cover is hinged and has 2″ thick Styrofoam insulation on top. I’ve also nailed up insulation strips to get a good seal. These measures keep heated air from escaping into the attic in winter and condensing on the roof framing.

Final Words

So if you’re new to CIRS and you’ve read this article, you may be freaking out. Please don’t. If your HERTSMI-2 mold test came back under 11, then there is a very good chance your place is just fine. Knowing about the importance of cleaning air conditioners and dehumidifiers should help keep you out of trouble in the future. If you’re inspired like I was to take extra measures, you’ve got some good information to work with. Be well.

4 thoughts on “Clean Fresh Air

  1. Perhaps this comment belongs on your Air Oasis post, but since you’re talking about air conditioning here… I live in New England and have heat by forced hot air including central A/C. My equipment was approaching 20 years old and probably was the source of some mold so I decided to replace it all (except the duct work which I’ll be having professionally cleaned shortly).

    At the recommendation of a mold inspector, I had dual PCO generators installed in the new equipment. The first is part of the Lennox PureClimate air filter assembly which includes 5″ filter media plus a UV-based PCO generator. The second is a Global Plasma Solutions GPS-2400 which is installed on the supply side before the AC coils. So the generated particles flow over the AC coils which is nice.

    This was installed just last week so I have yet to determine whether the enhanced filtration and PCO generators are providing any benefit. It looks like the GPS-2400 is small enough to be mounted inside something like a split system. So I’m wondering whether you ever considered installing something like this in your home’s systems rather than the UV bulbs.

    Lennox PureAir Filter

    • Cool information. At the time I was working on UVA air purification, I didn’t know much about PCO technology and would have probably been very skeptical. Nowadays, I’m seriously considering installing a whole house unit. We’ll see how it goes with the portable Air Oasis I purchased. So far I haven’t noticed any negative side effects. You may want to look at the YouTube I posted in the Air Oasis article that Caleb Rudd from Toxic Mould Support Austrailia told me about.


      Whole House Air Oasis Drops HERTSMI-2 From 12 to 4

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