Hi, I’m choosing an ERV, I live in Ottawa, Ontario where for several months it hovers around -20C, and dips to -30 for several days in FEB. I have a heart condition, so I need the ERV’s supply air coming in as consistently as possible.

Let’s say I’m getting a VanEE ERV which is rated for cold climates. It has recirculation defrost.

How long and how often does it have to go into this mode when it is -20-25 C for extended periods? Does it last for a few minutes or an hour?

I’m wondering if there be long stretches’ of no fresh air during these periods. With my heart issues, do I really need a pre-heating coil or or some other work round?

Or maybe there’s another model with more consistent supply in cold climate?

Because I’m also considering Renewaire. Their promotional material claims it doesn’t need a drain pipe, has “static-plate, enthalpy-core Energy Recovery Ventilator” and “never freezes, up to -10F”. But I don’t know if that means it would supply air with fewer interruptions or not. And I can’t find their -25 ratings.