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Community and Q&A

Sizing an HRV unit

Gary Bruzzese | Posted in Mechanicals on

Hello, community,

I am renovating my 1903 2 1/2 story colonial house in southern connecticut, zone 5a. The house is listed as 2,100 sq ft (ground floor + 2nd floor), but I am also finishing and including the attic into the building envelope, giving an additional 1,050 sq. ft. for a total of 3,150 sq. ft. of conditioned space. I will be using closed cell spray foam insulation in all walls and roof. Heating is hydro air, and cooling is central air. System is split on 2 units, one for 1st floor and one for the 2nd floor and attic.

My question is in regards to the size of the HRV units. I am going to install 2 units and connect them to the return duct of each air handler. I called tech support at Fantech, and they recommended that I use 2 SHR1505R units. These units cover up to 3,600 sq. ft.. each and deliver between 50-149 cfm. According to my ASHRAE 62.2 calc, the whole house only needs 61.5 cfm. (3,150 sq. ft./100) + ((3 bedrooms +1) * 7.5)

So it seems to me said the rep at Fantech grossly oversized the unit. Also, should each HRV provide the 61.5 cfm, or should I split it between the 2 zones of the house? In other words, 1,050 sq. ft. first floor and 0 bedrooms, so 10.5 cfm required for one unit. Unit for 2nd floor and attic would require 51 cfm (2,100 sq. ft. and 3 bedrooms).

Hope this makes sense and thank you all in advance for your help,

Gary

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Gary,
    To serve the needs of your house, one HRV is enough.

    The problem is your attempt to use ducts designed for heating and cooling for ventilation. Ideally, you would install dedicated ventilation ducts instead of trying to shoe-horn your ventilation system into your heating system.

    For more information on this topic, see .

    You don't have to have ventilation ducts leading to every room in your house. There are lots of ways to design this type of ventilation system. You might find it easiest to just pull your exhaust air from your bathrooms, and deliver your fresh air to your living room, and maybe one or two bedrooms.

  2. Gary Bruzzese | | #2

    Thank you Martin,

    Few follow-up questions...

    -I've read about both having and not having separate exhaust fans in bathrooms with HRV systems. I like the idea of a dedicated exhaust fan due to the larger amount of cfm' sit will draw out quicker. Would this be an option even with HRV exhausts in bathrooms?

    -the house layout has 2 bathrooms on 2nd floor, a bathroom and a kitchen on 1st floor, 3 bedrooms on 2nd floor, an office and a playroom in the attic. Only exhaust in the 3 bathrooms and kitchen? What about a kitchen exhaust fan?

    -a dedicated system brings some additional issues I wasn't previously thinking about it. Any articles on common ways to navigate duct work from the attic to the 1st floor? All interior walls and exterior walls are 2x4

    Thanks again,

    Gary

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Gary,
    Here's an article that provides information on your first question: Does a Home with an HRV Also Need Bath Fans?

    Concerning question #2: Your ventilation system can be as simple or as complicated as you want. If you want to have an exhaust grille in your kitchen ceiling, you can. Just don't try to connect your range hood to your HRV. If you want an exhaust grille in your kitchen, it should be located as far away from your stove as possible.

    Concerning question #3: Here is a link to an article that might help you: .

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