Last month, in Part One of a two-part series, we discussed how Zehnder owners in smoke impacted areas managed their Zehnder Comfosystems during the summer’s wildfires.  In the second part of this series we’ll talk about things to consider when preparing for a wildfire event.  First, let’s talk about some basics.

Zehnder HRV and ERV Function Refresher

Zehnder Comfosystems bring fresh air into buildings to provide healthy ventilation for occupants. The typical ventilation design is based on 0.3 ACH, or one complete air change of the living space every three hours. Having an HRV or ERV is crucial to ventilate today’s modern buildings because they are designed to be built tight and reduce the air leakage from building defects like cracks and voids, while moving the fresh air intake to intentional clean filtered supply intakes.  Along with getting the fresh air in, the Comfosystems include filters that can reduce the introduction of particles and allergens from the outdoor air. The goal of the Comfosystem is to do these functions with the least amount of energy penalty possible by running the intake and exhaust flows across a heat recovery core to ensure the fresh air flows experienced inside the home are as close to room temperature as possible.  

Why Wildfire Smoke Sucks

In addition to the destruction of wilderness, property, and life, wildfire smoke is hazardous to human health. The EPA is clear about why smoke is so dangerous to human health: “Smoke is made up of a complex mixture of gases and fine particles produced when wood and other organic materials burn. The biggest health threat from smoke is from fine particles. These microscopic particles can penetrate deep into your lungs. They can cause a range of health problems, from burning eyes and a runny nose to aggravated chronic heart and lung diseases. Exposure to particle pollution is even linked to premature death.”[1] So, even though the smell may be what we notice most when there is a wildfire, it is the particles that we don’t see that are most damaging to your health.

What a Zehnder System Can and Can’t Do

Zehnder Comfosystems are designed to bring fresh outdoor air into buildings. When the air outside is contaminated with smoke and fine particles, the air coming inside contains smoke and fine particles. The extreme level of this that we are experiencing on the West Coast is new, and brings new concerns. The onboard standard filters in a Comfosystem were designed to filter fresh air up to a MERV 13 rating. The extreme conditions we are experiencing contain much higher volumes of particles and gases that are too small to be caught in a MERV 13 filter.  There are additional options.  Whether from a wildfire, or a neighbor’s indoor or outdoor burning, having an additional Comfowell filter case with the optional MERV 15 or activated carbon filter, will reduce the amount of fine particles and/or smoke smell in your home. The effectiveness is in relation to the size of particles and the type of filter being used. The finer the filter, the better the success. The success is measured in the percentage of particles captured. It’s never 100%.

The highest filtration level available is a HEPA filter. It will further reduce the air particulates that may make it into your home. While the addition of a Comfowell filter case can accept up to a Merv 15 or Activated Carbon filters, it cannot accept a HEPA filter. They are just too large to fit in the Comfowell. A HEPA filter can be added as a separate filter in addition to the Zehnder Comfosystem. There are a few points to consider when doing this to ensure the placement and added static pressure don’t reduce the overall performance of the Comfosystem. Usually this can be solved with a quick call to Small Planet Supply.

Where Filtration Happens in a Zehnder System

The Zehnder system unit has two filters.  One filter is for incoming air to ensure that the air going over the transfer plates (heat exchanger) is clean, keeping the heat exchange core in good shape as well as purifying the air.  A second filter, for the outgoing air, captures particles from the home and prevents them from building up in the heat exchange core. 

An additional option for filtration is a secondary filter box that attaches to the Zehnder system’s Comfowell component. 

The Comfowell is attached to the top, or separate mounting position, of the Zehnder Comfosystem and contains a number of important system components:  a mounting kit, silencer, manifold and a ComfoPost (for heating or cooling) if one is used.  Each Zehnder Comfowell system configuration is unique as systems are designed for each home (or project’s) specific requirements.

If your system doesn’t have an additional filter box and you want one, you can order one from Small Planet Supply. 

Planning for Next Fire Season

Now that the basics are out of the way, let’s get into strategy.  With this year’s fire season over (at least for most of us), the last thing anyone wants to think about is next year.  However, a little bit of pre-planning can help you feel more ready for whatever next year’s fire season might bring.  We’ll start with Zehnder America’s recommendations and get into some other things you might want to consider.

Zehnder America Guidance

Zehnder America offers three tips for managing your Zehnder system during a wildfire smoke event:

1. Depending on the severity of outdoor air conditions, it is best to run your H/ERV on a lower fan speed or shut off the system completely. The speed you select depends on the tightness of your building envelope.

2. Consider using Zehnder MERV 13 rated onboard filters and additional MERV 15 or activated carbon filters in an additional Comfowell Filter Case to increase the level of filtration. If your system is equipped for added filtration, these filters will minimize exposure but not completely neutralize it.  For best results, change your filters regularly.

3. If possible, monitor for CO2 levels inside your building and take advantage of periods of improved air quality to use natural ventilation to aid in your home’s ventilation efforts.  Small Planet Supply has a CO2/Air Quality monitor recommendation under the Particulate Section of Six Areas to Consider.

If you’re thinking you want to delve deeper into the subject, we’ve identified some areas Zehnder Comfosystem owners might want to consider when developing their smoke strategies.

Six Areas to Consider When Developing Your Wildfire Smoke Strategy

1.    What type of filters/filtration you already have in your system

Increasing the filtration can reduce the amount of smoke and particulate that makes its way into your home. As mentioned previously, the Zehnder systems work with two filters – one for incoming air and one for outgoing air. These filters are either a G4 (MERV 7/8) or an F7 (MERV 13).  If your incoming air filter is a MERV 7/8, replacing it with a MERV 13 filter will provide additional filtering.

If you live in an area that experiences wildfires often or for long periods, you may want to use an additional filter box that will attach to your system’s Comfowell.  The Comfowell filter box can be fitted for either an F7 (MERV 13), F9 (MERV 15) filter or the Activated Carbon Filter. Check to see if your onboard incoming filter is a G4; simply increasing the filtration to an F7 would improve the quality of air.

2.    The amount of particulates in the air

Looking outside is one (not always effective) gauge of how bad the air quality is, but there are other ways you can determine air quality. In order to find get information about the current air quality in your area, you can to go the EPA’s  website called AirNow.gov.  There are also iPhone or Android phone apps you can download to give you air quality information, useful apps are: Air Bubbles by Wynd Technology and Air Quality Breezometer.  iPhones also have an air quality index inside the Weather App so you can get the information without even downloading an app, if you choose.

 Knowing how much smoke is in the outside air (and being able to take advantage of short periods of better air quality) can better help you identify the best periods of time to open up your windows or run your system to let fresh air into your house.

If you’re in an area where wildfires are frequent and of long duration, it’s also important to know what the air quality is like inside your house.  Joe Medosch, Healthy Building Scientist with Hayward Score, recommends the Awair Element, which not only measures CO2, but also measures air quality.  When using the monitor, focus on the particulates and the carbon dioxide levels ,as the TVOC readings can vary widely. You can order it directly from the company by clicking here.  

3.    The length of time your system is processing smoky air

The longer your home is experiencing wildfire smoke, the more you’ll want to make sure that your filters are working properly and that your fans are running at the right speed for conditions.   The right choice may actually be turning your system to “away mode” or turning your system off, in which case you’ll want to consider how fresh air will be getting into your home while your Zehnder system is turned off. 

If your area is experiencing low levels of smoke over extended periods of time (months), you’ll want to check the incoming air filters are still relatively clean.  If filters are excessively dirty, you’ll want to change (or wash them) even if the elapsed time hasn’t been as long as standardly recommended (3-6 months).

4.    The level of airtightness in your home

If you are living in a tightly constructed home and you are turning off your system, you’ll need to monitor the air quality in your home, especially the levels of CO2.  If you have made the decision to turn off your system, this may mean opening your windows at times when the air quality is better during the day (or night) or turning on your system to refresh the air in your home. As discussed in Consideration #2, running the Comfosystem at the boost rate might be better option than opening a window since the incoming air from the Zehnder will pass through filters.

5.    Greater concern about smoke smell or particulates

If you are concerned about the particulates coming into your home, you will want to pick a MERV 15 filter for your Comfowell attached filter box.  If you are more concerned about smoke smell, you will want to select an activated charcoal filter.

Using an indoor air purifier unit that has a CADR rating of above 350 can also improve the air quality in your home. This means it has been verified by ADHM so it should be a good bet. Check to see what filters cost before purchasing the unit. If you purchase an air purifier, you may want to put a charcoal filter in your Comfowell since the air purifier will be able to provide extra air filtration for the air inside your home.

6.    How much work you are willing to do to ensure the best quality air

There are many steps you can try to both ensure your Zehnder is operating (or not operating) optimally during smoke conditions. However, homeowners don’t always sign on to be climate scientists or system engineers, so for them easy is good. Other system owners love to tinker with their system.  

Whether you want an out-of-the box solution, or want to know about other options available now and in the future, read on.

Low Effort Wildfire Smoke Strategy

If you’re a homeowner who just wants simple actions to take during a fire event, this is what you may want to try.  We recommend checking to see if your incoming filter is an F7 to increase the amount of particles that will get trapped before they go into your system and changing filters if they are excessively dirty.  Turn your system to a lower speed to reduce the amount of smoke that is brought into your home. If you choose to switch to away mode, or turn your system completely off, use a CO2 indoor air monitor to ensure CO2 levels don’t get too high and an indoor air purifier to clean air in an area or areas of your home (if needed).

Small Planet Supply Offers Alternative Solutions for the More Adventurous or Impacted

The first solution we’ve been working to provide for owners is a HEPA filter system that cleans air before it goes into your Zehnder system.  Since the fires started, we began investigating HEPA filter systems that would work with  Zehnder Comfosystems.  After evaluating several systems, we identified the Hawk Airwash system as the best choice.  The Airwash filter, like all HEPA filters, are rated to remove 99.97% of airborne particles .3 microns and larger, including airborne smoke particles. The Airwash itself has three stages: a foam pre-filter, the HEPA stage, and a carbon stage, for the final ‘rinse’ of the air. These filters, with proper care, can last up to five years.

The Airwash filter system is suitable to use in conjunction with a Zehnder HRV, retrofitted into a forced air system, or run on an independent loop. 

If you plan to integrate this HEPA filter into an existing HRV system, give us a call and we can help guide the process. Your HRV may need additional balancing with the introduction of a new filter. The filter system, as well as filter replacements, are available on our online stores (Canada -coming soon | USA).

A Second Automated Solution

Another area we’re investigating is a system that monitors involves outside air quality with an outdoor AQI sensor and automatically adjusts the Zehnder system fan speed accordingly.  We’re working with the inventor to continue development on the product and if it does well after testing, we hope to make it available to our customers. 

Hopefully the wildfires that happened last year don’t occur again, but if they do, a little advanced planning can help you feel more prepared.  If you have concerns about your Zehnder system, feel free to contact Small Planet Supply.  If you’d like to know more about how to perform routine maintenance on your Zehnder system, including how to change your filters, you can enroll in our free Zehnder Maintenance Course on Small Planet Supply’s Learning Platform.

**We are not engineers, climate scientists or fire experts, nor do we play them on TV, so guidance provided here is subject to our limited (but hopefully helpful) understanding of Zehnder Comfosystems.

[1] https://www.epa.gov/indoor-air-quality-iaq/wildfires-and-indoor-air-quality-iaq