Combustion Air Intake Efficiency / Heat Recovery Ventilators

Discussion in 'HVAC Heating & Cooling' started by jjohanson, Feb 2, 2009.

  1. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Question:

    1. What is the most efficient way to bring combustion air from the exterior?

    • Can/should heat recovery ventilators be used to bring in exterior combustion air?

    Background:
    I am converting an old church building to a two family residence. The building has a small boiler room in the basement which has no intake of exterior air, except what comes through the interior. For the conversion, I need to fire separate the boiler room, and based on this volume, there is not enough interior combustion air to meet code; my code officer requests that I pull exterior combustion air.

    The most straightforward solution is to send the code required ducts to the exterior, which are fairly large as the total BTUH are in the 650k range. Another option is to use an expensive forced ventilator. I am wary of EITHER of these cases, as they would bring in cold exterior air to the boiler room; it seems that some of the heat from the boilers would be lost to this colder air temp - isn't this the case?

    Another possible option: I've seen many different types of heat recovery ventilators (HRV). These are typically used to Exhaust stale air, but can you use these as combustion air intakes if you just exhaust both the "stale" and heated fresh air into the boiler room (rather than exhausting the "stale" air to the exterior). Based on the energy consumption of the HRV, would it even be worthwhile in this application?

    I'm looking for any ideas or perspective on the situation.
    Thanks!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,149
    Location:
    New England
    My unprofessional opinion, bring the air directly from outside. Do not try to use a heat recovery system for combustion air. Colder air is denser, and you may need to adjust the burner based on that rather than doing it in the summer during maintenance.Now, the building may benefit from the use of a heat recovery ventillation system, but for the people, not for the furnace.With a HRV system, you'd be exhausting air you'd already conditioned to warm the intake of the furnace and then throw it out the flue...doesn't make sense to me.
  3. CarlH

    CarlH New Member

    Messages:
    175
    Location:
    Northern VA
    I'm unprofessional too. ;) I agree, it does not make sense to use a HRV for this purpose. You are looking at using the HRV to supply combustion air with the exhaust going through a vent other than the HRV. HRVs expect approximately equal flow in both directions for the heat to be exchanged correctly between the inlet and exhaust air. I would expect that if incoming air flow is significantly higher than the exhaust, it would be same as a venting air directly from the outside. Use an HRV to get rid of pollutants in the house like radon.
  4. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Thank you for the responses.
    Makes sense now that the HRV would not work in this scenario.
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