Below is a quick guide to some of the more common questions asked about Zehnder products. For more information, please reference other Zehnder documents on our website or contact us directly at 1-855-367-7442

+ What size Zehnder unit do I need for my project?

The basic ventilation rate formula under ASHRAE 62.2 recommends 7.5 CFM per person in the home plus 3 CFM for every 100 sqft of enclosed building area. Passive Houses have different requirements, however. The best way to ensure an accurate sizing is to request a quote on Zehnder’s website. You can find the link to that page here

+ What’s the difference between an HRV or an ERV?

Both the HRV (Heat Recovery Ventilator) and the ERV (Enthalpy Recovery Ventilator) provide continuous ventilation needed in today’s airtight homes. HRVs utilize a heat-exchanger core that captures the heat from outgoing stale air and applies it to incoming fresh air. The ERV core is made from advanced materials that allow not only heat but also moisture from outgoing air to diffuse into the fresh incoming air. This is especially important in cold climates when the ambient outside air temperature is below freezing and the relative humidity is at or near zero.

+ Is the ducting UL listed?

The ComfoTube ducting is not UL listed, however the ComfoFlex ducting is. Be sure to check in with local building code to see what is required in your area.

+ What are the electrical requirements?

All of the Zehnder HRV’s require a 208/230V single phase, 50-60Hz connection with a dedicated 15-amp breaker.

+ What is recommended for exterior duct terminations?

We supply a stainless exterior wall grill for use with Zehnder’s ComfoPipe insulated exterior ducting. Intake and exhaust locations should be at least ten feet apart in order to avoid cross contamination, and if either exterior duct run is longer than 15 feet, you’ll need to upsize your duct’s inner diameter by an inch.

+ Do exterior duct runs need to be insulated?

Yes, exterior duct runs must be insulated to R5 or better with air/vapor-impermeable insulation to prevent cold intake air from causing condensation to form on the duct. We recommend Zehnder’s ComfoPipe, which is already insulated, airtight and very simple to install.

+ Do interior duct runs neeed to be insulated?

Interior duct runs should only be made within the conditioned envelope of the building. Avoid routes through exterior walls, unconditioned spaces, and spaces that are under insulated.

+ How is the system balanced after installation?

In order to qualify for Zehnder’s warranty, you’ll need to have your system commissioned by a certified commissioner. You can start the process by submitting your request on Zehnder’s website and completing their pre-commissioning checklist, after which a representative from Small Planet Supply will reach out regarding payment and scheduling. You can find Zehnder’s webpage here.

+ How do I prevent the HRV/ERV core from freezing during the cold winter months?

It is important to have adequate frost prevention and depending on your climate, there are best practices available. Option One – Utilize a ground source Pre-Heater/Pre-Cooler. The Zehnder ComfoFond-L utilizes a ground loop of glycol and a small circulating pump to pre-heat or pre-cool and dehumidify incoming air with a hydronic coil. Option Two – Utilize an electric or hydronic pre-heater. By warming the incoming air prior to entry into the H/ERV, frost is prevented. Option Three – Imbalance flows to allow for warm exhaust air to defrost unit. This option either slows or stops the incoming, cold air while allowing the exhaust air to warm the Heat Exchanger’s surfaces and remove frost.

+ What is summer bypass and how does it work?

During summer nights and in the shoulder seasons of spring and fall with strong sunshine, the house can become too warm, while the outside temperature remains pleasantly cool. In such cases, heat removal by what is known as “free cooling” helps: the Zehnder ComfoAir units are equipped with a standard automatic bypass for just this purpose, and diverts 100% of the relatively warm extract air from the heat exchanger, introducing cool supply air to the space.

+ If I install a Zehnder in my project, do I need to have bathroom and laundry rooms fans, a kitchen range hood, etc.?

If return diffusers are installed in the bathrooms or laundry rooms, you will not need an extract air fan as the HRV will effectively replace them. A kitchen range hood will still be required, however except in Passive House designs by a certified Passive House Consultant.

+ Do I need a condensate drain for the Zehnder system?

You will need a condensate drain, which Zehnder provides in the form of a waterless p-trap, which will need to be connected to the home’s drainage/sewer system as per code. This is required for all HRV systems. The ERV systems do not require a condensate drain as they recirculate the moisture that passes through them.

+ What kind of maintenance is required for these HRVs?

Maintenance of the Zehnder HRV’s is limited to periodic cleaning or replacement of the filters accessible from the front of the unit. The exchanger core should be inspected and cleaned annually (depending on the outside air quality). Please see the unit manual for additional servicing tasks.

+ What is Zehnder’s Warranty policy?

When installed according to the applicable Zehnder America, Inc. Installation instructions and the applicable local, state, and federal building codes and unless specified otherwise, all Zehnder America, Inc. products sold in North America carry a two (2) year LIMITED WARRANTY (from the original date of shipment by Zehnder America, Inc.) covering defects in the original manufacturer. For a full warranty policy, please visit Zehnder America’s website at ZehnderAmerica.com.