Furnace cold air return requirement with HRV
sbabcock61
| Posted in Building Code Questions on
New build in Ontario with Zehnder ComfoAir 550 HRV (home run system – not tied into furnace)
Does the furnace need traditional cold air returns in various rooms or can we just draw air back into the furnace directly from the basement (where the furnace is located)
The HRV is already moving air so not sure of the purpose of the cold air returns in this setup
Steve
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Replies
Steve,
The forced-air system that includes your furnace has an entirely different purpose from your HRV system. The furnace provides heat; the HRV provides fresh air.
The air flows involved are different by an order of magnitude. Many HRVs operate at 80 cfm, while it's common for a furnace to operate at 800 cfm.
HRVs have such low air flow rates that they are incapable of pressurizing or depressurizing a room strongly enough to create problems.
A forced-air heating system, on the other hand, can easily pressurize a bedroom strongly, causing all kinds of home performance problems (including increased air leakage through the home's thermal envelope and condensation problems).
So, the bottom line is that forced air systems need return air systems to prevent individual rooms from being pressurized. Here is a link to an article that explains more: Return-Air Problems.
Thanks for the clarification - I'll checkout the article