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  1. #1
    Join Date
    Jan 2005
    Posts
    21

    Question

    In my non-professional and somewhat ignorant thinking, it seems that with all the spot ventilation (3 bathrooms, range, dryer, central vac) a balanced ERV would still leave a house negatively pressurized?

    I believe in some cases (winter) negative pressure may be desirable, however the concern would be back drafting (wood fireplace)? Summer might warrant a positive pressure to help prevent moisture being pushed in?

    I plan on sizing spot ventilation appropriately, not over sized. Hot water heater will have a Balanced Combustion System. In-floor radiant heating and mini-split ductless AC. Icynene insulation. The only make up air would be from ERV, which would only balance with itself, not the additional spot ventilation. True??

    How concerned should I be with a negatively pressurized envelope? Are there ways to maintain a neutral/positive pressurization? Or, is my thinking completely bassackwards?

    I am not looking for a specific design (although that would be nice), just some opinions from all you envelope/ventilation experts on how to balance ERV with spot ventilation.

    Thanks in advance for educating me.

  2. #2
    Join Date
    Apr 2002
    Posts
    11,808
    With the ERV being balanced, then intermittent use of 'spot ventilation' will cause intermittent imbalances. If combustion air issues are addressed, and there is not a radon problem in your area then I do not see this as being a problem.

    Big exhaust appliances such as a Jenn Air, or elaborate kitchen hoods will require a make up air system in most cases.

    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  3. #3
    Join Date
    Jan 2005
    Posts
    21

    Lightbulb

    Thanks Carnak.

    Intermittent imbalance! For some reason my thought process was stuck on a constant imbalance due to spot ventilation exhaust. I realize from searching earlier posts, that maintaining a consistent pressurization is nearly impossible.

    I am planning on a Jenn Air Range, however not the down draft type. My range hood will be elaborate looking, but the fan will be less than 200 CFM as the various guidelines indicate for a 30" range.

    I believe combustion air can be addressed within a fireplace, and I definetly want it addressed with the water heater.

    I am probably being overly anal. Not hard to do reading so much about radon, co, moisture control, etc. I have yet to actually engage a contractor, only breif conversations at home shows, and get a design specific to my plans. I think I am ready to go talk to builder, truss designer, architect, hvac, etc. What honey, you want to move the bathroom where?

    Considering that the concept of mechanical ventilation is extremely new to me, I am just trying to get a good base understanding of options, designs and considerations.

    Thanks for your input.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,341
    Where do you live? It makes a big difference on the style of ventilation. Green grass climates have a much higher moisture load. Basement homes are more sensitive to high humidity. For indoor air quality, it's important to ventilate to purge pollutants/replacing oxygen, while maintaining <50% relative humidity to prevent mold and dust mites growth.

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