Three Types of Filters that Help Your Zehnder Keep Indoor Air Clean

MERV rating Chart

From the moment outside air enters the system, a Zehnder system (and its filters) are designed to keep air contaminants from entering your home, while efficiently recovering heat (or cooling) from the air exiting your home. 

Do you know every level of filtration available to you for your Zehnder recovery ventilator? If you’ve recently installed one of these units, or purchased a house that included one already, you hopefully know of (and are changing) at least the in-unit filters. These two filters, one for supply and one for return air, do the brunt of the filtration work to keep your unit running efficiently and delivering the cleanest air, but there are a few other filters that complement the system.

Filters Inside the Unit For Supply & Exhaust Air

G4 + F7 filter Set

We hope you’re familiar with this first set of filters, since you should be checking them seasonally and changing them at least twice a year! The supply and return filters inside the actual HRV/ERV unit are the main defense against air particulates. These filters come in either MERV 7/8 or MERV 13 filtration level, Zehnder calls these G4 and F7. MERV, or Minimum Efficiency Reporting Value, is the standard for measuring how well a given filter performs and what particle size it filters down to.  In Zehnder recovery ventilators a MERV 7/8 is typically used in the return side of the unit, this is to filter the air returning to the unit from your house. Since this air is expected to already be fairly clean and free of particulates, the MERV rating of this filter can be lower and is mainly there to protect the unit from large particulates. The supply side is where the MERV 13 filter will go, and that is doing the bulk of the filtration work. The supply side is filtering air coming from the outside, so you want the highest level of filtration here, not only to ensure the longevity of the internals, but also to make sure the cleanest air is delivered to your home.

Additional Filtration for Specific Circumstances

For extra levels of filtration, you have the option of adding in an extra filter box. Known as the ComfoWell Filter Housing, this goes inline with the supply piping and allows the addition of one of two types of extra levels of filtration. The ComfoWell Fine Particle Filter is a MERV 15 rated filter, these are rated to filter out bacteria, most tobacco smoke, & droplet nuclei (sneeze). This series of filter is a great addition for those seeking higher levels of filtration than the standard filters offer, especially those with allergies and other air quality sensitivities.

COMFOWELL FILTER HOUSING

ACTIVATED CARBON FILTER

FINE PARTICLE FILTER

Alternatively, the ComfoWell filter box can be configured to accept an activated carbon filter. While the activated carbon filter isn’t intended to filter out particulates, where it excels is in capturing chemicals and odors. This filter is impregnated with activated carbon which bonds with and neutralizes chemicals and odors. Great for locations near busy roads or industrial areas with odors and can make a difference during forest fire season. Worth noting is that the ComfoWell Filter Housing can only take on or the other of these additional filters, so you need to make a choice based on what your needs are. Both types of ComfoWell filters should be changed at least every 6 months.

Not Sure if Your Unit Has a Comfowell?

The picture on the right shows a Comfowell installed over the system silencer. Comfowells will be installed either over or under the system silencer. If your system doesn’t have a Comfowell installed and you are interested in installing one, contact Small Planet Supply. Comfowells are available for all Zehnder systems except the CA 70.

Some Zehnder systems are installed in locations where there isn’t room to add a silencer, but hopefully you’re system has some space to install a Comfowell if you so desire.

Filters for Unit Protection, Efficiency and Longevity

This last, oft forgotten filter is still an important piece of the filtration system and contributes to the longevity and proper function of the equipment. These filters are the return register filters, which come in two types, dependent on which kind of return register your system uses.

If using the circular STB or Venezia style return diffusers, a conical filter will be used just behind the register.

If using the rectangular Roma style boxes, a rectangular mesh filter exists for use behind the decorative cover on these.

RETURN DIFFUSER CONE FILTER

Return diffuser panel filter

The function of these two filters is the same, they protect the system from house dust and other airborne particles before they enter the return pathway. This keeps the piping and the inside of your Zehnder unit free of dust buildup which can impede airflow and cause the system to work harder, lowering efficiency. These mesh style filters can be washed and reused a few times throughout the year, but it is still a good idea to replace these at least once a year.

That all may seem like a lot of filters to check and replace throughout the year, but most systems will only have three different filters, those being the two filters in the unit, and the return diffuser filters. Checking these seasonally and replacing when needed, or at least once a year (every six months for the filters inside the unit), is a small task compared to the amount of work these units perform to keep your home properly ventilated while wasting as little heat as possible. Zehnder systems perform at the top of their class, with select units achieving 92% recovery efficiency.

Small Planet Supply is your source for all of your Zehnder filters, parts, planning, and commissioning. Visit our newly redesigned webstore to get your filters today!

Still confused about which filters to order for your Zehnder system? Check out Josh Palmer’s visual Zehnder Filter Selection Tool.