ERV connected through HVAC or individual runs
We are having a Panasonic or RenewAire ERV installed. Currently, plans are to connect into the main supply and return of the house. With this setup, we will run the fan continuously since it will have an ECM motor.
Another option our builder posed is using the same brand ERV, but instead of running it through the main HVAC, running individual runs to multiple rooms in the house (laundry room, bathrooms, walk in closet…) making the ERV it’s own separate system (that’s my understanding at least).
Is there a best practice as this would replace exhaust fans for these areas? Is the extra cost of doing it this worth it? The main thing we’re hoping to avoid is moisture/humidity issues in the home or ducts.
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I did a halfway in-between. I have 4 exhaust pickups, one in each of the three bathrooms and one in the kitchen. I may add a small vent to my basement as well. Then the return feeds into the return of my HVAC system. My ERV is the Renewaire Premium L, so a pretty big one. It peaks at 280cfm. My HVAC blower is a similar size, since it's a small Hydronic air handler, a Briza 22. I didn't use bathfans, just this system. My 2nd floor bath that is the furthest away may need aa boost. One could add a bathfan as a booster if needed.
All that said - I haven't run my system yet. Our house is still a few months from completion.
I wonder, will connecting the ERV to the return air duct cause a higher negative pressure on the ERV supply air and cause it to pull in more outside air? What happens when the AHU isn't running? I guess the outside air from the erv might end up making its way through the supply duct of the AHU but it might not make it to all the diffusers.
I have it branched into the return. I also have an oversize return duct on the AHU. So in the case where the AHU is not running, the ERV would push air back out that return path.
+1 On Tim_O's setup. I've done it a couple of times and works great. Key is to have good return ducting so it there isn't much static pressure when the air handler runs.
This gets you most of the benefit of a home run setup with half the ducting. You also save all the bath fans and wall caps so cost wise it is pretty much a wash.
Make sure to install a boost switch in the kitchen as well, this is the one that I use the most.
If it was on an entirely separate ducting, do you see this causing any issues? Also should we request boost switches for the bathrooms and kitchen?
Why are you installing the ERV? Curious as to what problem you are hoping to solve.
It is best practice for the ERV to have it's own supply and return duct runs, but the amount of difference it makes depends largely on how airtight your home is. Have you ever had a blower door test performed? If your house is relatively air tight, then it would be a good idea to replace the bath fan exhausts with the ERV stale air pickups to avoid negatively pressurizing your home. But keep in mind, in most cases the CFM moved through the ERV ductwork will be less than what your traditional bathroom exhaust fans can move, so you will need to run them for longer and it will not clear the humidity from those rooms as quickly.
There are other options with boost mode and motorized dampers, that may help bring the CFM exhaust capabilities of the ERV closer to what you had with the bath fans. But you would have to upsize the ERV ductwork to handle the boost mode air flow to each room.
We are building a new home and because it will be tight, are leaning towards the ERV having its own runs as your described to the bathrooms, laundry, kitchen and walk-in closet. They are designing it currently so that it can be on a main control to run all the time, with additional timer options on the bathrooms only should we decide not to run it all the time. We’re hoping to avoid humidity issues and other issues that could lead to poor air quality or mold.