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HRV with pre-heat

Russgs | Posted in General Questions on

I am building a house in cold climate of Calgary Alberta. I am planning on installing separate duct distribution system for my HRV based on Zehnder’s recommendation. It will be a good house (R30 walls R50 attic triple glazing) but nothing over the top. I hate to put holes through my envelope unless I have to so I don’t plan on installing any dedicated kitchen or bathroom exhaust fans. I will use the HRV to exhaust from the kitchen and bathrooms and have a boost switch in each area to turn the HRV on to high speed. 
I do plan on having an electric pre-heater so I can run the HRV without freeze up issues but should I look at a post heater in case I need ventilation when temperatures get down to -20 or colder. 
I have been looking for a hydronic post heater but the only one I can find is made in Ireland ??
A hydronic post heater would be perfect since i have a boiler installed for in-floor heating for the lower level of the house.

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  1. MattJF | | #1

    I would run an ERV as most of them don’t have freezing issues or need drains even in very cold environments.

    If you do any real cooking, there is a huge advantage to capturing fine cooking particulates at the source. I strongly recommend an exhaust in the kitchen.

    I have a ducted mini-split going in along with a fully ducted ERV. I am going to experiment with a motorized damper teeing the ERV supply to the mini split return. The damper will open when the mini split is running, drawing all the fresh supply air into the mini split. This avoids cold supply air and improves mini split efficiency by dropping the return air temps. You need an ECM ERV or constant volume damper to keep the ERV balanced. It is also experimental...

  2. this_page_left_blank | | #2

    Post heater will not be required. The amount of air coming out is small enough that you won't notice it. Especially with pre-heating.

  3. Expert Member
    Akos | | #3

    I 2nd the ERV. Much better choice. You don't want a pre-heat as this would actually reduce the amount of heat the ERV/HRV transfers (if the air going into the ERV is warmer, the core transfers less heat from the stale air, thus you loose more heat in the exhaust).

    The post heat is the better setup, I would just put a hydronic duct coil (standard HVAC item, nothing special) in the fresh air supply with a TRV with remote sensor in the air stream. Typical post heat for a 100CFM unit is around 300W, so you need only a very small coil.

    I have a 75% efficient ERV and when it dips to -20C, the air coming out is definitely bellow room temperature. If this goes into your HVAC inlet, than not a big deal. If it is fed directly into a room, you would notice it.

    Range hood is a must, I would not skip the kitchen exhaust. Cooking fumes would gum up the core in an HRV/ERV, you want a stale air pickup in the kitchen, but it should not be somewhere where it will pick up cooking fumes directly (kitty corner from the stove is a good spot).

    Typical 100CFM ERV/HRV does a decent job of exhausting one bathroom, even there a bath fan works better. If you have more than one bath, I would put a dedicated exhaust fan for each additional bath.

    1. Russgs | | #4

      Thanks very much. Good advice. Could you tell me where to find a hydronic coil that small?

      1. Expert Member
        Akos | | #5

        Check your local HVAC suppliers. Most likely you won't find anything under 1 ton. A replacement coil for a hydronic toe kick heater probably a closer match.

  4. frankcrawford | | #6

    I designed and built my passive house in Calgary and have lived in it for 3 years (Montgomery Passive House), here are my comments: you need an ERV to keep the RH in a comfortable range for most of the year. You need to reduce the ERV fan speed to low in the winter as well or your RH will drop. You need a bigger then standard electric pre heater to keep the Zehnder running below -15C. Small planet workshop sells larger electric pre heaters and hydronic post heaters. If you only have eclectic cooktops (preferable induction so you don't burn anything) you can use a recirculating hood fan plus the ERV exhaust at least 8feet away from the cooktop, also put a grease filter in that exhaust. Contact me directly if you want and have more questions.

    1. this_page_left_blank | | #7

      The need for ventilation doesn't drop in the winter. Lowering the ventilation rate in favour of higher humidity is misplacing priority.

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