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  1. #1
    Join Date
    Apr 2019
    Location
    California
    Posts
    80

    Question Energy Recovery Ventilator vs Exhaust Fan

    Our course this week I had the privilege of inspecting a new build.

    It had 3 bathrooms, 2 of which had exhaust fans, however the 3rd had what looked like at time a return air supply duct without a filter.

    Well, I called it out for not appropriate ventialtion in the bathroom and the builder came back sayings it has a ERV system connected. (Odd 1 of 3 had this), Anyway there was not an on/off feature for this ERV system, and attic acess was blocked off so I could not check the unit.

    My question is, are ERV's suitable and are the considered a replacement for the mechanically vented requirement ?

    Builder reply "There is a fresh air fan installed in your attic servicing this hallway bathroom and the laundry room"


    Any information on this matter would be appreciated.

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  2. #2
    Join Date
    Mar 2007
    Location
    Fletcher, NC
    Posts
    28,030

    Default Re: Energy Recovery Ventilator vs Exhaust Fan

    Hopefully Gunnar will reply with California specific requirements. Until then, this is from the IRC:

    TABLE M1505.4.4
    MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
    AREA TO BEEXHAUSTED EXHAUST RATES
    Kitchens 100 cfm intermittent or 25 cfm continuous
    Bathrooms-Toilet Rooms Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous

    An ERV could ... could ... work as long as it meets the minimum required ventilation of 50 cfm minimum for on/off exhaust fans or 20 cfm for continuous (no off switch) exhaust fans.

    Designing an energy recovery component to a bathroom exhaust fans seems as though it would only work with a continuous fan.

    Jerry Peck
    Construction/Litigation/Code Consultant - Retired
    www.AskCodeMan.com

  3. #3
    Join Date
    Apr 2019
    Location
    California
    Posts
    80

    Default Re: Energy Recovery Ventilator vs Exhaust Fan

    Quote Originally Posted by Jerry Peck View Post
    Hopefully Gunnar will reply with California specific requirements. Until then, this is from the IRC:

    TABLE M1505.4.4
    MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
    AREA TO BEEXHAUSTED EXHAUST RATES
    Kitchens 100 cfm intermittent or 25 cfm continuous
    Bathrooms-Toilet Rooms Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous

    An ERV could ... could ... work as long as it meets the minimum required ventilation of 50 cfm minimum for on/off exhaust fans or 20 cfm for continuous (no off switch) exhaust fans.

    Designing an energy recovery component to a bathroom exhaust fans seems as though it would only work with a continuous fan.

    Thank you Jerry, I was not sure if ERVs came into the classification of exhaust fans.


  4. #4
    Join Date
    Mar 2007
    Location
    Fletcher, NC
    Posts
    28,030

    Default Re: Energy Recovery Ventilator vs Exhaust Fan

    Quote Originally Posted by Joe Reilly View Post
    I was not sure if ERVs came into the classification of exhaust fans.
    That would depend on the design of the ERV.

    ERVs are basically a pipe from inside air to outside air with a chamber around it to allow transfer of heat between the two to allow heat generated for the inside to be transferred to the cold air coming in from the outside, or cooled air generated for the inside to be transferred to the hot air coming in from the outside ... very basically speaking.

    If the 'pipe' is connected to a bathroom exhaust fan, for it to work with efficiency, the exhaust fan would need to be on continuously, or switched on from two locations: the bathroom when that is in use; and/or the heating/cooling system when ithat is in use. If the fan was already on for one use, and the other use then called for the fan to be on, neither "on" switch would shut the fan "off". Both fan switches would need to "off: for the fan to turn "off".

    Noncontinuous operation requires 50 cfm minimum when on. Continuous operation only requires 20 cfm and to be continuously on.

    Seems to me like they may be trying to eliminate one penetration through the thermal envelope, which makes sense, if done correctly.

    Jerry Peck
    Construction/Litigation/Code Consultant - Retired
    www.AskCodeMan.com

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