Zehnder Comfosystems

Systems with heat recovery for a comfortable indoor climate


Built It Tight? - The Next Step Is: Ventilate It Right.

Zehnder ComfoSystems provide clean, fresh air, 24 hours a day - 7 days a week.  

The solution to making comfortable energy efficient homes, heat recovery ventilation (HRV), captures the heat energy from the exhaust air stream and returns it to the incoming air stream. The two air steams never touch each other. Only the heat energy is moved. It works the same in cold or warm conditions.  If it's hot outside, the heat is kept outside. If it's cold outside, the heat is kept inside. It doesn't require force, or more energy than is used by refrigerator light bulb. It's just physics in action: Heat moves from hot to cold.

Zehnder’s Comfosystems are Extremely Quiet and Have High Sensible Recovery Efficiency

Heat recovery ventilation has been in use here in North America for the last 30 years. North American equipment available has been in the low to moderate performance range based on heat transfer efficiency. The common problems with the mid-level equipment has been noise and performance. Once installed, a noisy unit is often turned off by the occupants to stop the continuous background noise. A poor heat transfer efficiency unit can work adequately in temperate conditions but will be uncomfortable during the warmest or coldest months by blowing hot or cold air over the occupants due to it's poor efficiency. When the sensible recovery efficiency (SRE) is high (85% - 93%), the incoming flow of air is the closest to the indoor temperature as possible. This means fresh air is flowing into the living environment within a comfortable range of the indoor temperature by extracting the energy from the exhaust stream being vented out of the home.   

Zehnder’s Comfosystems Technology is a Quality Product for Today’s Building Standards

While HRV's have been slow to evolve in North America, the technology has been perfected in Europe over the last 15 years by the 100 year old, $250 million Zehnder Group. Zehnder HRV’s arrived in North America in 2010 to service new high performance projects built to the German Passivhaus Standard - the most stringent building standard in the world today. As the movement for energy efficiency expands to all homes, this simple method of heat and energy recovery ventilation easily moves with it.

It just becomes a question of quality. Quality is in the experience. Or the lack of experiencing noise or uncomfortable air.

Zehnder Frequently Asked Questions Architects & Builders

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.

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 th 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.

How to get a Zehnder System

Request a System Quote.

There are two ways to add a Zehnder ventilation system into your project:

Add a Zehnder unit into a standard sheet metal distribution system.  (Please contact your HVAC Contractor).

Use the full capacity of Zehnder ComfoSystems with the ComfoTube distribution system and design services by a Zehnder engineer.

A full Zehnder system is designed to replace the volume of the building enclosure with fresh air every three hours. The filtered fresh air is distributed through the Zehnder ComfoTube to each location without the use of trunk lines to ensure design flows are met for every room. The Zehnder ComfoWell Silencers reduce noise even at boost levels.

To learn more about how the system works, please read the ebook.


For help with a Zehnder ComfoSystems project, just give us a call or email: (360) 866-8779 -or- info@smallplanetsupply.com. To shop for Zehnder system accessories, select the icon for your country to shop the Small Planet Supply store online:

Zehnder Information Request Form

Have Zehnder questions or want more information about Zehnder? You can call Small Planet Supply at 1-855-367-7442 or use this form to request additional information. *
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Zehnder Videos 

How to Install: part 1

How to Install: Part 2

How to install a ComfoAir 70

Additional resource pages

Learn more at a workshop -  See if there are any upcoming workshops.

Education - What is an HRV , why you should have one, and how to maintain it.

Request a system quote - See the description in the sidebar for more info on full system quotes.

Installation - How to install your Zehnder HRV.

Commissioning - Making sure your Zehnder HRV is set up properly.

Learn more about our network of advisors and installers.

See the Zehnder product list. Most items in stock for immediate delivery.

Online Zehnder Courses Offer Architect CE Units

AEC Daily is one of the largest providers of continuing education (CE) to the Construction, Architectural, Interior Design and Engineering communities. Their complimentary courses automatically report earned credit numerous organizations across the United States and Canada. Zehnder has two courses to help building professionals.

The first Zehnder video, Heat Recovery Ventilation: Why Efficiency Matters, focuses on understand how their HRVs and ERVs help keep energy costs down through its high level of energy efficiency.

The second Zehnder video, Healthy IAQ in Energy Efficient Buildings, addresses the indoor environment in our homes and how using a balanced ventilation system improves indoor air quality.

The best part of these courses is that they are available 24 hours a day, 7 days a week, so you can take these courses when it's convenient for you.  To enroll in either of the courses, click here.