Running Ducting for the ERV
The Zehnder ventilation system relies on a lot of ducting tubes.
Tight houses need air exchange. Period. Our target air exchange rate for this house is less than 1 ACH50 and with a goal like that, a clean source of fresh air will be necessary.
This was our first time using the Zehnder system. We’ve relied on another heat-recovery ventilator (HRV) product in the past that we’d chosen for cost and speed of installation. One of the knocks against this other system is the operating noise. I was interested in the Zehnder for its silent operation, the 84% heat recovery efficiency, and that I could spec an energy-recovery ventilator (ERV).
My number one suggestion when choosing to use the Zehnder system is to integrate it into the design of the house. Given the number of flexible 3 in. pipes required for supply and exhaust vents the system is much better suited for a house designed with open webbed joists or dead space above the ceiling and still in conditioned space. Our TJI floor system in the FHB House meant that many holes needed to be drilled. Many holes. I spent a lot of time scrutinizing the TJI span and hole chart. In the end, it all worked out and we were able to get all the 3 in. pipes where they needed to go.
For the FHB House the system has ten 3-in. supply pipes that serve the living room, bedrooms, and common areas. There are also ten, 3-in. returns that exhaust air from the bathrooms and the kitchens. Each 3-in. pipe provides the same flow rate of air, so in areas where more exhaust or supply is necessary, the number of pipes is increased. For example, in the exhaust vent in kitchen ceiling connects to three pipes to triple the flow rate. Conversely, at the small gathering area at the top of the stairs, only one supply pipe is necessary because the space is so small.
The ComfoAir 350 is a nice system. It runs quietly and the house is well balanced. Homeowners have the option to boost the exhaust of the entire system for a period of time if the taco meat from the previous evening’s dinner didn’t sit right or they have a big house party and know their guests will be blowing a lot of hot air over cocktails.
The biggest take away for me is that it is important to plan for the system in the design of the house. If planned for properly, then the installation will be a breeze and the house and occupants will benefit for years to come.