Understanding Ventilation to Get Fresh Clean Air at Home

What Is An ERV – Overview

We are going to dive deep into this topic, but if you want the TLDR version, here it is: There are many potentially harmful pollutants that come from outside the house, inside the house, and from the occupants of the house. ERV stands for Energy Recovery Ventilator, and an ERV exchanges heat between filtered fresh outdoor air and stale stagnate indoor air. This allows the ERV to pump fresh outdoor air into the house and exhaust the undesirable indoor air multiple times per day without hurting your heating bill. If you want to learn more, check out our blog post, or just keep watching this video. 

Why Houses Need Fresh Air

Our homes are great at trapping harmful concentrations of pollutants. Volatile Organic Compounds or  VOCs for short can be though of as anything that you can smell. A beautiful flower naturally produces VOCs and your perfume or cologne may synthetically produce a similar smell through the use of VOCs. There are other VOCs that are naturally produce, let’s say… when you use the bathroom, and although they may not be pleasant that doesn’t necessarily mean that they are harmful.

However, there are VOCs that are produced during the manufacturing and construction of all homes that can be harmful. If these VOCs are not vented out of the house, they can cause harmful side effects that may be temporary or permanent. Over time these VOCs will break down and stop being a risk just like that New Car Smell that fades away over time. On that note, the VOCs that make the New Car Smell everyone loves is caused by the off gassing of plastics, adhesives, and expanded foam. Most VOCs will stop off gassing sometime after 6 months, but SVOCs Semi-Volatile Organic Compounds may take years. Not the best for our health which is why a ventilation strategy should be implemented in new construction homes.

A very common ventilation strategy in Colorado is radon mitigation, but that only focuses on one indoor air quality metric. Since we live in Colorado which is designated as “Zone 1” by the EPA for elevated levels of Radon the air you breath in your home most likely contains dangerous levels of radioactive radon gas which is why radon mitigation systems are commonly installed. You may already be familiar with Radon and the health risks that come with it, but if you aren’t, check out our radon page, blog posts, or videos about this topic. Ultimately radon needs to be exhausted from the home to keep the occupants safe.

Another gas that needs to be exhausted from the home is carbon dioxide which is what we breathe out of our lungs with every breath. The air we breathe out can have a negative impact on our cognition if the air in our home, office, or home office is not properly exchanged with fresh air. A 2021 study affectionately titled “Associations between acute exposures to PM2.5 and Carbon Dioxide indoors and cognitive function in office workers: a multicounty longitudinal prospective observational study” found a direct correlation between poor indoor air quality and a reduced cognitive function. It is clear that fresh air exchanges can lower the parts per million, PPM, of CO2, but how do we combat PM2.5?

Why Houses Need Air Filtration

PM2.5 is either a solid or liquid Particulate Matter suspended in the air that is smaller than 2.5 microns. To give context to that number the EPA has a diagram that shows the average human hair being between 50-70 microns wide against the size of 2.5-micron spheres. It may be possible to see inhalable particles such as dust, dirt, soot, or smoke, but PM2.5 is so small that an electron microscope is needed to see it. PM2.5 compounds can be so chemically complex that understanding how they came to be inside your house is impractical, so we should just focus our energy on filtering it out.

ERVs pass the air inside your home through a filtration system at least 8 times per day and many ERVs come with a MERV 13 Filter. MERVE, Minimum Efficiency Reporting Value is a rating that goes from MERV 1 to MERV 16 followed by HEPA, High Efficiency Particulate Air [Filter]. MERV 13 can filter out 90% of particles from 1 to 3 microns. Which means that MERV 13 is a perfect starting point for home filtration.

Why A Furnace Can’t Filter Your Home’s Air

Most forced air furnaces have air filters that are MERV 5 which can capture about 20% of particles sized 3-10 microns. So, why not just replace your old cheap filter with a MERV 13 filter?

First the better the filter the more air is restricted from passing through the filter. This can be circumvented by purchasing a pleated filter to increase the surface area that the air can pass through but depending on your furnace, upgrading the filter while still maintaining the furnace’s heating and cooling efficiency may not be possible. In addition to causing higher utility bills installing a restrictive filter may also reduce the service life of your furnace.

Secondly even if the airflow was not restricted the furnace or AC unit doesn’t run constantly throughout the day and night, but instead it will turn on for a short period of time and then be shut off for a longer period. Additionally, the furnace only recirculates the air inside of the home so even if it were possible to meet the required number of air exchanges per hour to adequately filter the air in your home, which it isn’t, the air would still have high levels of VOCs and CO2.

If your home is heated by a hydronic system such as in-floor radiant heat, there is absolutely no significant filterable air movement in the home. If you want to learn more about hydronic heating systems check out our videos and blog post. Unfortunately, many homes with in-floor radiant heating systems were not built with a ventilation strategy in mind. What were these builders thinking to build a house without a ventilation strategy?

What Is An Air Tight House

Believe it or not most houses were built to save the homeowner money at the time of construction. There are thousands of small decisions that are made during construction of a home that can save money upfront but cost the homeowner a significant amount of money or heartache during the life of the house. These choices result in higher utility bills, uncomfortable temperature swings inside the house, increased number of pests entering the home, issues with moisture such as mold and rot just to name a few.

All of these issues have one root cause and that is a poor control of air movement in and out of the house which in turn results in poor control of moisture movement in and out of the house. The idea of a “tight” house is nothing new, but after decades the requirement to build tight houses is finally starting to be written into the code book, but what is a tight house? Tight houses can most easily be thought of as a house that doesn’t allow air to enter or exit the house independently of a mechanical air handler. A tight house prevents the movement of air which prevents the movement of water vapor and since there are fewer holes in a tight house, pests are less likely to enter the home. If the ventilation strategy is well balanced there is no such thing as too tight. This idea is proven by projects like the International Space Station, Biosphere 2, and the thousands of submariners around the world.

Are Tight Houses Better

When houses are properly ventilated a tight house is significantly better than any traditional house in every metric, but if the house is not properly ventilated a tight house will amplify issues such as high humidity caused by cooking and bathing much more than a traditional house would. Why is that and how do we quantify it?

A standard test performed to test the air tightness of a house is called a blower door test. The door will either push air into the house or suck air out of the house. The unit of measure used is ACH50 which means Air Changes per Hour at 50 pascal. Pascal is a unit to measure pressure, but you are probably more familiar with PSI or pounds per square inch. Most car tires are inflated to 35psi and to put ACH50 into perspective 50 pascal is equivalent to about 0.007 psi.

The 2003 Study, Analysis of US Residential Air Leakage Database, reviewed the data from 70,000 homes in the US and found that the average American home had a blower door score of 10 ACH50. Thankfully in 2009 the building codes were updated to require homes to be at 7 ACH50. In 2021 the codes were updated again to require homes to be at 3 ACH50 with a leniency of up to 5 ACH50 given to homes that implement other energy saving measures such as Heat Recovery, HVAC Sizing Calculations, or an Improved Thermal Envelope to name a few. There is a standard call the Passive House Standard requires homes to be at or below 0.6 ACH50.

A whole video series could be dedicated to tight and passive house construction, but there are plenty of impressive builders that can show you all the new technology and processes that make these houses truly remarkable such as Matt Risinger and the Build Show Network.

Humidity in the house from cooking and bathing can cause issues with mold and rot, but a house with 10 ACH50 will have a much easier time dealing with it when compared to a house with 3 ACH50. So what happens if a house has 0.6 ACH50? Well… If the house is properly ventilated, nothing at all, but if the house isn’t properly ventilated and dehumidified the house will very quickly become uncomfortable to live in and start to decay. The quality of the build is only as good as the quality of your ventilation strategy.

What Is Better HRV or ERV

There are two main types of mechanical ventilation, and they are Heat Recovery Ventilators, HRVs, and Energy Recovery Ventilators, ERVs. Don’t let the name fool you, they both do the same thing, but and ERV has the added function of also transferring humidity.

To help us understand the difference between HRV and ERV systems lets refer to HRV and ERV systems as ERVs as get an idea of the basic mechanics. To introduce fresh air into the home the ERV draws in air from the exterior of the house using a fan and passes it through a filter, normally a MERV 13 or better. The fan then pushes the air into the house and the house becomes filled with fresh air. If the House were 10 ACH50, then that would be the end of the story because all the air being pushed into the house would displace all the old air out to the exterior and your house would be ventilated using positive pressure. Unfortunately, as the air is being pushed through and out the house doors will be slammed shut as the air pass by, windows will be difficult to operate, and during the winter, all that fresh air would be freezing cold, and the inside of your house would be just as frozen as the great outdoors. If the house was a tight house, the new air would have nowhere to go and the ERV would do nothing.

The second function of the ERV is to exhaust the stale air that is inside the home. A fan draws in the stale air, passes it through a filter and then exhausts it out of the house. Hopefully the amount of air going out is the same as the air going into the house, otherwise if the exhaust is too strong you might get a negative pressure which would slam doors shut as the air moves the opposite direction, the windows would be difficult to operate, non-filtered air full of allergens and pollutants would be drawn into the home, and your house would be cold during the winter. If the house was a tight house the ERV would be inefficient and ultimately fail prematurely. One important note is that an ERV that creates a low-pressure condition in the house will undoubtedly create a severe health hazard by drawing radioactive radon gas into the home. I can’t make this point any more clear, radon gas is dangerous, radon mitigation should always be a separately managed part of your ventilation strategy and properly balancing an ERV’s intake and exhaust is critical.

The third function of the ERV is to transfer heat from one stream of air to the other. “There is something very important I forgot to tell you, don’t cross the streams”. The fresh air coming into the house should never be mixed with the stale air going out of the house, but it is imperative that the heat be allowed to transfer. The center core of the ERV has channels for the air that are perpendicular to each other and sandwiched together. The core material allows heat to transfer from one air stream to the other. The direction of heat transfer is always from hot to cold because hot air has more energy than cold air which means that the cold air will draw the heat away from the hot air. During the Winter the cold air coming into the house will be warmed by the already warm air being exhausted out of the house. During the Summer the hot air coming into the house will cooled by the already cold air being exhausted out of the house. What this means is that the air coming into the house should match the temperature of the air exiting the house which is a type of energy recovery that happens during ventilation, and that is how ERVs got their name, Energy Recovery Ventilators.

 The fourth function of an ERV that separates ERVs and HRVs is the ability to transfer moisture between the two airstreams. An HRV’s non-permeable core can only transfer heat, but and ERV’s permeable core is made of a material that can capture moisture and transfer it to the airstream with a lower humidity level. This type of core allows homes in humid climates to remove humidity from the outside air before the air enters the home. In arid climates like Colorado many homes are humidified to increase the home’s comfort and an ERV will allow the humid air inside the house to be transferred to the incoming air instead of being exhausted to the exterior. The two issues with ERVs that need to be addressed is that ERVs will need a condensation drain line for the condensate that is trapped but not transferred to the air, and the correct winter ready ERV will need to be purchased to prevent the core from freezing as cold winter air enters the ERV. HRV systems are being replaced by ERVs in cold climates as anti-freezing technologies advance.  An ERV system works great in warm and cold environments by keeping humidity levels inside the home different from the levels of humidity outside of the home.  

Is An ERV A Dehumidifier

An ERV can keep the humidity inside and outside of the house at different levels, but an ERV is not a Dehumidifier. One important part of a ventilation strategy that is often overlooked is that a dehumidifier should always be installed with an ERV. In an arid climate like Colorado the homeowner may want to install an ERV, Dehumidifier, and Humidifier.

It might seem silly to install a dehumidifier and humidifier, but there are many examples of when it might be necessary to have both. A dehumidifier is essential in a tight house. Cooking, doing dishes, bathing, watering plants, working out, and breathing all increase the levels of humidity in the house. An extreme example could be taking a steam shower after a hard workout every day. An ERV will transfer the humidity from the steam shower into the incoming air thus trapping the humidity in the house. The stacked effect of each of those showers will cause the humidity to rise inside the house until the dew point is reached causing condensation on the ceilings, walls, and windows. This condensation will result in damage and mold growth. A dehumidifier will reduce the humidity levels in the house to the level that you prefer keeping the house mold free and comfortable.

Let’s say you don’t take long steam showers, you don’t cook very often, and you have no houseplants… Well, your house will become very dry and uncomfortable as the Colorado air strips away any humidity trapped in your house, which is why you might want to install a humidifier. The humidifier will keep you house comfortable and an oasis away from the dry air of Colorado while your ERV still provides you with fresh Colorado mountain air, but what happens during ski season when friends or family come to visit? Now a house that was conditioned for very few occupants has adults and children leaving wet ski gear all over the house to dry, cooking huge meals, taking showers much longer than any reasonable person would take, and then leaving their wet towels to slowly dry all over the house. At this point your house will become overly saturated with humidity and without a dehumidifier your house will be damaged by the condensation as mold begins to grow leaving you with allergies and water streaks staining your walls and as your friends or family finally leave your house, they will wave goodbye saying see you next season. As houses get tighter it is imperative to implement a ventilation strategy that not only provides fresh air but also humidity and dehumidification when needed.

What IS A Smart ERV

Smart ERV systems have monitors that can control the ERV and other systems in the house. Smart ERV systems can detect levels of particulate matter, carbon dioxide, VOCs, temperature, humidity, and pressure. Smart ERVs can tell you when to change the filters based on detecting particulate matter. Integrated carbon dioxide detectors can increase air flow when you have guests over or decrease the flow when no one is in the house. A smart ERVs can increase air flow if it detects higher levels of VOCs which can happen when cooking, applying perfume, using cleaning supplies or installing new furniture like a couch. Temperature sensors can ensure that the house is being properly heated and can run defrost cycles if the core starts to freeze during an extreme cold weather event. Smart ERV’s can be used to control humidification and dehumidification systems to ensure that the home stays well balanced. Smart ERVs can also adjust the flow of incoming and outgoing air to counteract the negative pressurization effects of turning on a dryer, range hood, or bathroom fan. Smart ERVs can even be adjusted to apply a slight positive pressure to your house to make sure that pollutants like smoke from wildfires don’t enter your home through any nooks or crannies that may not be air sealed.

The American Society of Heating Refrigerating, Air-Condition Engineers or ASHRAE for short recommend 0.35 Air Changes per hour with no less than 15 cubic feet of air per minute. That is equivalent to a blower door score of 7 ACH50, give or take. Their recommendation is a minimum and even with the best smart ERV providing significantly more air to the home than the ASHRAE standard, it is still possible that your house could have poor air quality for many reasons. Some systems are installed by eye and proper measurements and calculations are not made. It is important to understand that evenly distributing air through the house may be great from a number of occupants per total house size, but that doesn’t account for the fact that the majority of the occupants time might be spent in a small home office that can end up having poor air quality levels while the rest of the unoccupied house has phenomenal air quality. This type of an issue can be mitigated by having air quality sensors in rooms that can also have their air flow rates automatically adjusted by the smart ERV.

Conclusion

This topic is expansive, and we have just barely scratched the surface. Regardless of if your house’s construction is loose or tight you would still benefit greatly from investing in an ERV, but as you can see the help of an HVAC specialist might be necessary. If you have any questions or if you would like to schedule a home inspection, please visit TwoMooseHomeInspections.com, Have a wonderful day.