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Options for Updating Your HVAC System for Better Indoor Air Quality

There have been a lot of discussions and varied information on how the built environment affects the spread of COVID-19. Now, we are also seeing more intense wildfires and smoke than we’ve seen in the past decade. With both these environmental issues keeping people indoors, healthy ventilation strategies are more important than ever.

October 29, 2020

Ventilation in buildings has entered into the cultural zeitgeist of 2020 for some unfortunate reasons. Normally, we would be discussing ventilation in buildings and how it relates to managing the usual culprits of pollen, dust, cooking odors, humidity, VOCs, etc. This year, however, is unlike any we’ve seen in our lifetime, and addressing proper ventilation in your home, apartment building, or commercial space as it relates to the management of air-borne disease and wildfire smoke is more important than ever.

With simple, but well designed and considered ventilation systems, all those unwanted and potentially dangerous elements in the air can be mitigated to provide occupants with a clean, comfortable, and healthy living and working environment.

Why are we talking about ventilation now?

A big reason ventilation has been in the news and discussed on podcasts during this pandemic is that it’s commonly overlooked when it comes to design, construction, and maintenance.

Think about your personal living situation right now. If you close all your windows, do you know how outdoor air is entering your home? What about the indoor air after having the windows closed for several hours — is that air just stuck inside or is it getting out somehow? Think about your heating and/or cooling system. Do you know if it’s bringing in any outdoor air or is it simply recirculating the indoor air? If you don’t know the answers to these questions, it’s worth your while inspecting your current heating/cooling system.

So, what can you do to address your existing ventilation system?

It might seem like an easy fix, but simply turning up the fan speed of your HVAC or switching the fan from “auto” to “on” does not solve the problem. It only passes recirculated air over the filter more frequently and does nothing to replace the air in your home. Running the fan all the time also wastes energy and can prematurely wear out the motor in your HVAC system as they are not designed to run 24/7.

This is what I recommend.

Learn About the Filter Options Out There

The world of filters is a complicated one. There are different numbers for different types of filters, and even filters with the same performance are numbered in different ways, making it difficult to determine what the best option is without a little background knowledge.

If you’re going to update your filter, find one that meets the MERV 13 rating or better. MERV stands for Minimum Efficiency Reporting Value and is the industry standard measurement for filter performance, similar to the N95 rating on masks. You might also see MPR or FPR ratings on filters. MPR is found on 3M Filtrete filters and a Filtrete 1900 is equivalent to a MERV 13. FPR is a rating on Home Depot branded filters and you want to look for an FPR 10 filter. MERV 13 filters are the minimum level of filtration recommended by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers to filter out coronaviruses.

An HVAC installer will be well-versed in the different filters available, which leads me to the next point.

Call in a Professional

A qualified HVAC installer, especially one who specializes in high-performance ventilation systems, will do the best job of evaluating your current system. They can determine whether it’s safe to install a MERV 13 filter on your existing system.

The reason we don’t recommend going out and picking up a 3M Filtrete 1900 filter before having your system evaluated is that higher performance filters are also more restrictive. It’s very similar to the difference between wearing a cloth mask and an N95 mask: it’s harder to breathe in an N95 mask than a cloth mask because the N95 is a significantly more effective filter, and the closeness of the fibers requires your lungs to exert more pressure to move air through the mask.

Determine Your Existing System’s Compatibility for More Robust Filtration

Your furnace feels the same way your lungs do when you’re breathing through a more restrictive mask. It’s important to make sure your furnace can handle the increased resistance without damaging it. An HVAC technician has the tools to measure the pressure in your current system and determine what level of filtration will not reduce the life of your system.

Furnace filters also come in different thicknesses. A 1" filter is the most common, but filters are available in up to a 4" thickness. The thicker the filter, the more surface area available, and the less restrictive it is for your HVAC system. An HVAC tech can help evaluate if you can retrofit a larger filter box into your ductwork to accommodate a thicker filter.

Consider Adding an Outdoor Air Supply

In addition to better filtration options, adding an outdoor air supply to your existing system is an option to help dilute the pollutants in your indoor air. (The new MERV 13 filter you’re hopefully installing filters the outdoor air passing through it.) These come with controllers and automated damper valves so the correct amount of fresh air comes in, and only when your HVAC system is running, to help mitigate the difference in temperature between the outdoor and indoor environments.

Sometimes Upgrades Just Aren’t Possible

Depending on where your HVAC system is located, it may be more difficult to install an outdoor air supply unit. It is also dependent on having a ducted heating and cooling system. Traditionally, homes in the Pacific Northwest don’t have central air and, in those cases, none of the upgrades discussed would apply. In these types of homes, if you only have baseboard heaters, you are not getting any air movement when you are heating your home.

If you’ve installed a window A/C unit, or several, you can adjust these to let in some outdoor air, however, the filtration on these units is notoriously poor and there is no easy way to improve it.

Many modern buildings in the PNW condition with ductless mini-splits. These are very efficient, but are only able to recirculate the air inside, and also have limited filtration abilities. For these homes, there are options available but improving the airtightness of the building envelope would be the first priority.

You’re not entirely out of options, though. If you like taking a DIY approach, a quick internet search can give you some ideas for how to convert a box fan to filter and circulate the air inside your home. There are even some handy videos that will walk you through step-by-step.


This post is part of a series discussing ventilation and indoor air quality in response to the ongoing COVID-19 pandemic and worsening air quality along the Pacific Coast due to wildfires.

More From This Series on Ventilation and Indoor Air Quality

How a Heat Recovery Ventilator Can Make Your Home Healthier

Indoor air quality has never been a more pressing or popular target than it is today. With smoke from wildfires all over the West and the continuing global pandemic of COVID-19, many of us are wondering whether our indoor air is safe. The good news is it can be with the right systems in place. Find out more in How a Heat Recovery Ventilator Can Make Your Home Healthier.

Tips for Ensuring Your Home Has Good Air Quality

With wildfire season continuing into the late fall and a global pandemic still keeping millions of people indoors, there's a lot going on in the world. Both these natural disasters have brought to the forefront the importance of ventilation for your health: well-designed ventilation in buildings is important to address present and future pandemics, wildfires, and other airborne pollutants. Learn more in Tips for Ensuring Your Home Has Good Air Quality.

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Tips for Ensuring Your Home Has Good Air Quality

With wildfire season continuing into the late fall and a global pandemic still keeping millions of people indoors, there's a lot going on in the world. Both these natural disasters have brought to the forefront the importance of ventilation for your health: well-designed ventilation in buildings is important to address present and future pandemics, wildfires, and other airborne pollutants.

How a Heat Recovery Ventilator Can Make Your Home Healthier

Indoor air quality has never been a more pressing or popular target than it is today. With smoke from wildfires all over the West and the continuing global pandemic of COVID-19, many of us are wondering whether our indoor air is safe. The good news is: it can be, with the right systems in place.

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