Running ERV Through Existing Ductwork
green654
| Posted in General Questions on
We just bought a newly built
house and we want to add an ERV. The new construction “new house” smell is a major irritant to me. Since the walls are already constructed, it’s too late to have a dedicated ducted system. So the only economical way to do it is to run the ERV through the existing ductwork. Obviously, installing an ERV with its own ductwork is the best way to do it. But will running it through the existing ductwork help our situation at all? I need fresh air brought into the house. I can’t open windows all summer because of the humid climate so relying on windows being open is not an option. Thoughts?
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Another option would be to install multiple Zehnder ComfoAir 70s or, if you are in a heating-dominated climate, Lunos e2s.
But connecting an ERV to the existing ducts is likely easier.
Will it work to provide fresh air even if running through existing ducts?
The ComfoAir 70 and Lunos e2 units are installed in the wall. They do not tie into any existing ducts. I think of them as "spot ventilation" devices since they serve relatively small spaces.
You can install it on the return side but the caveat is that your air handler will need to run whenever your ERV is running.
One thing you can do is program your ERV to run at full speed during 20 minutes and let it rest during 40 minutes so you don't have to run your air handler all the time.
You can use the existing ductwork.
My preferred method is the hybrid ducted setup shown here:
https://www.finehomebuilding.com/2014/11/05/ducting-hrvs-and-ervs
In your case, you can run one stale air pickup to a floor register in the kitchen area (kitty corner from the range about 8' away) and one to the basement. No need to run any returns upstairs unless you have an existing duct chase you can fish them through.
For this setup to work well, best to select an autobalance ERV (ie Panasonic Intellibalance / Zehnder Q series / Broan AI). These automatically adjust to the change in pressure in your return duct as your furnace cycles and keep the flow through the ERV balanced.
You also want a motorized damper on the outside fresh air in interlocked with the ERV (some units like the Panasonic IB has this built in). This way if the ERV is not running, the air handler can't draw in outside air through the ERV which might cause the core to frost up.
If you interlock the air handler fan with the ERV it can provide better mixing in the house. This works well if you have an ECM blower in the air handler that can be set to a low flow rate.
If it is a PSC blower this is not the best as these can use a lot of power running it all the time.
You can also not interlock the two. In this case the fresh air will be supplied to the house through the existing return vents when the furnace is not running and you'll get mixing each time the thermostat calls for heat/cool. You can also program most thermostats to run the furnace fan periodically to mix.