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ERV ducting

Kay_Esper | Posted in General Questions on

Hello people,

i need your valuable advice with my situation, i am planning to install an ERV, home is solid walls airtight, about 1500 sqf with 4 occupants.
question 1: flexible ducting or square sheet metal solid duct?
question 2: manifold with 8 inch intake split to 6 ports of 4″ for the fresh air and 8 inch manifold split into another 6 ports of 4″ for the exhaust. is it better or if i run an 8 inch round metal duct with 6 inches connections to each room. where i live they don’t install ERVs otherwise i would have called a contractor, but i’m doing the homework myself. 
so a manifold is better than main tube with inlets/outlets to each room? and how much does it affect the capacity of the ERV as per calculations i only need about 100 CFM

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  1. ConstableBrew | | #1

    Hi Kay_Esper - I'm in a similar situation to you both home size and ventilation CFM needed. What solution did you end up with?

    1. Kay_Esper | | #2

      I ended up with 200 cfm at high speed that I can run 150 at medium speed to preserve lifetime of the ERV I got the daikin vam 350 you only need 120 to 150 cfm depending on the ducting system if there's a lot of pressure drop you will lose pressure and you need to compensate, i ran 2 main trunks at 8 inches with 3 inches flex outlets from dampers at the main trunk im pleased with the results

  2. Expert Member
    Akos | | #3

    100CFM is not much airflow. As long as you keep the layout simple and no bends using flex pipe, you don't need more than 6" duct. You can bump that up 7" if your layer is more complicated.

    Rooms need very little flow (10CFM to 25CFM), those can easily be handled with 3" duct. I like to use semi rigid aluminum pipe (think dryer vent but longer) as it can be easily run inside interior walls and around bend with any fittings.

    Stale air pickups would have to be larger, you want 65cfm out of the kitchen and the rest out of the bathrooms. This means a 5" duct to the kitchen and 4" to the bathroom.

    If the ERV and ducting is inside conditioned space, the house side ducting doesn't need to be insulated. Only the ducting that goes from the unit outside needs insulation, this should be well sealed and insulated. Un-insulated ducts take up much less space.

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