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HRV Main duct size

brad_14 Member Posts: 25
Hi all,

I am nearing the completion of my entire system and need help with the main HRV ducts.

The house is an 1800SQ' rancher + a walkout basement. THe boiler room is fairly central left right but closer to the front of the house. The HRV is an older Lifebreath 300DCS I picked up cheep (very cheep and it works well so far)it is connected to a Lifebreath 3000TFP Hepa to supply the house. The duct between the 2 is a 7" Flexible duct with a 7"x7"x4" breather T the 4" is open. The HRV is supplied and vented with 6" insulated duct to the outdoors. Currently the two are running. But that is where it ends the rough in in the main floor walls run through the floor into the basement, that's it. The Vent and supply are noted as U for upstairs or D for downstairs.

The sketch attached is pretty much to scale and vent locations. I need main vent and supply ducts running to the left and right should they be 6" or 7".

Any advice/wisdom on this or HRV ducts in general is greatly apreaciated.

The rest of the system is low temp outdoor reset joist trak on the main and in slab in the basement fired by a Triangle Tube 110.



  • hvacfreak
    hvacfreak Member Posts: 439
    all I know...

    is that for 150 cfm at .10 static ( @ 100 ft ) , I would go with 7 inch.

    I'm not sure about the heat exchanger recomendations ( perhaps slower air velocity from the building for better recovery ?

    If this were a commercial situation you could control a vfd from something like a temperature transducer on the leaving side of the hx ( fresh air in ) . A modulating damper might be a high tech option ( while I'm in over-kill mode ). Either of these ideas could incorperate freeze protection as well ( may not be an issue , but I do commercial work ).

    Perhaps 7 inch with manual dampers might be the best option.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    TFP ducting

    The TFP should be piped with a breather T, but should be attached to a 7" supply duct with a "bypass", rather than having the entire CFM load pass through the TFP. That won't work. I use balance dampers on both the inlet and outlet of the TFP to get 10% bypass of the HRV's output through the TFP. 7" ducting is recommended.

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  • Weezbo
    Weezbo Member Posts: 6,232
    As a thought...

    with lots of space...would maybe two HRV's work out a little better?

    sorry i thought that i read 18000 sq ft...

    rather tan get into it too much, look under Wisdom and Associates ...there is something there for you...

    I thinking and i too am pretty sure that you would want to filter say 300cfm's with like 90 with gradual filtration or dilution ...
  • brad_14
    brad_14 Member Posts: 25
    7\" does sound more apropriate

    Thanks guys I think 7" would be best. I wanted you to say 6" just for space concerns but I needed someone to tell me 7". The boiler room got pretty tight quick. Any other suggested locations for dampers. I do like the idea of Automatic modulating dampers(I love technical overkill but unfortunatly my wallet and wife want me to get the house done yesturday, maybe a future upgrade ;))
    Thanks again
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