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  1. #14
    Join Date
    Jun 2008
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    128
    Doesn't he say there will be an ERV installed? Wouldn't the "extra" intake are just flow in the ERV intake when there is negative pressure? You wouldn't get balance flow and the heat exchange would suffer, but I'm not sure how you would end up with negative pressure in the house if you already have a big hole (ERV) in place.

  2. #15
    Join Date
    Jun 2008
    Posts
    58
    Yes the house has an ERV. Yes the h20 and furnace are all direct vent. Cracking a window does seem very simple but when its 2 degrees out side not really on the efficient side of things.

  3. #16
    Join Date
    Jun 2008
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    128
    Quote Originally Posted by acnoob1 View Post
    Yes the house has an ERV. Yes the h20 and furnace are all direct vent. Cracking a window does seem very simple but when its 2 degrees out side not really on the efficient side of things.
    Unless there are mechanical dampers on the ERV that close when the unit is off, you shouldn't have a negative pressure issue....

  4. #17
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Quote Originally Posted by acnoob1 View Post
    Yes the house has an ERV. Yes the h20 and furnace are all direct vent. Cracking a window does seem very simple but when its 2 degrees out side not really on the efficient side of things.
    Honestly - you are concerned about a non-issue. That's all I have for ya. How much do you think it will cost you to heat a couple of hundered cfm every once in a while without it going through the ERV? It's nothing, man! Move on!

  5. #18
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
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    769
    Quote Originally Posted by patchesj View Post
    Unless there are mechanical dampers on the ERV that close when the unit is off, you shouldn't have a negative pressure issue....
    And that's true anyhow!

  6. #19
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,444
    I assume this home is in a cold climate? How many occupants. Having a make-up air inlet on your heating/cooling will provide fresh when ever the fan operates. This will make your ERV unneeded. I read you are going to have a finished basement. Any provision for supplemental dehumidification during wet cool weather when the a/c is not operating? Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #20
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Quote Originally Posted by teddy bear View Post
    I assume this home is in a cold climate? How many occupants. Having a make-up air inlet on your heating/cooling will provide fresh when ever the fan operates. This will make your ERV unneeded. I read you are going to have a finished basement. Any provision for supplemental dehumidification during wet cool weather when the a/c is not operating? Regards TB
    Why would you eliminate the ERV? I know the furnace will handle the load - but the ERV still provides a benifit by reducing the load - it's the whole point - constant fresh air with little energy penalty.

    The OP was more concerned with negative pressure issues from intermitant dryer/ range hood use... The ERV is kind of a seperate issue - except, as noted, the air intake of the ERV will "equalize" the building pressure anyhow... Further still - like you said - a small fresh air intake on the return would equalize building pressure - but it's the same energy penalty as a cracked window - which the OP laments.

  8. #21
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Acnoob, are you in a humid climate or a cold one? Because if your comment about 2 degrees out is true of your region, then it will be hard for humidity in the basement to be a problem. Any outside air below 60 degrees will have dewpoint guaranteed below 60F, probably a lot less.

    Try to completely describe what problems might occur due to exhaust air. If it is something like backdrafting a combustion appliance, then certainly that is a life threatening situation. But if it is just the "looks bad" of knowing there is negative pressure, you have not demonstrated a need. It could well be true that you are getting concerned about an issue which does not deserve it.

    Sure you could construct a system to pressurize the house only when the exhaust fans run, at least a fresh air intake to the HVAV return plenum could ensure the makeup air is filtered and conditioned. But could you please tell me why it is worth it.

    Lstiburek advocates if a house structure gets wet anywhere, it have a plan to dry out. All the house problems I have heard about, have been violations to that rule. The very fact dryer operation is intermittent, gives you a plan to dry out when the thing is off. Besides, when the outdoor dewpoint is lower than indoor then it is somewhat desirable to have a negative pressure as the chronic condition. Is there any problem you can foresee due to having occasional air outflow due to your appliances?

    Regards -- Pstu

  9. #22
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
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    769
    Quote Originally Posted by pstu View Post
    Acnoob, are you in a humid climate or a cold one? Because if your comment about 2 degrees out is true of your region, then it will be hard for humidity in the basement to be a problem. Any outside air below 60 degrees will have dewpoint guaranteed below 60F, probably a lot less.

    Try to completely describe what problems might occur due to exhaust air. If it is something like backdrafting a combustion appliance, then certainly that is a life threatening situation. But if it is just the "looks bad" of knowing there is negative pressure, you have not demonstrated a need. It could well be true that you are getting concerned about an issue which does not deserve it.

    Sure you could construct a system to pressurize the house only when the exhaust fans run, at least a fresh air intake to the HVAV return plenum could ensure the makeup air is filtered and conditioned. But could you please tell me why it is worth it.

    Lstiburek advocates if a house structure gets wet anywhere, it have a plan to dry out. All the house problems I have heard about, have been violations to that rule. The very fact dryer operation is intermittent, gives you a plan to dry out when the thing is off. Besides, when the outdoor dewpoint is lower than indoor then it is somewhat desirable to have a negative pressure as the chronic condition. Is there any problem you can foresee due to having occasional air outflow due to your appliances?

    Regards -- Pstu
    Nope - he already stated the furnace and DHW heater are direct vent.

  10. #23
    Join Date
    Jun 2008
    Posts
    58
    This problem might not be a problem at all like you have said. If the house is built properly then it should be tight. I need some source of fresh air. The ERV handles that for me. Then I possible could run into the problem of when expelling air threw appliances that i would have negative pressure, moisture would try to find its way in. From what I have been told that is when you run into problems. I guess I was trying to find a way to bring make up air into the house the most efficient way possible.

  11. #24
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by acnoob1 View Post
    My concern with just letting it dump into the basement. Is that the basement is finished and you would not want to dump hot humid summer air in.
    I was concerned about winter. If you have the powerful kitchen exhaust, crack the window in the kitchen, the extra bugs will be added protein

    to make the ERV work, then the ERV would be grabbing the range hood exhaust which is not a good idea, it will get all gunked up. The greasy air will also be humid, similar to the outdoor air so you would not benefit here, the greasy air could be even more humid than the outdoor air so the ERV in this application would be humidifying your make up air.

    You could interlock a make up air fan with the range hood and have it blow humid air into your return duct work. You could have the motorized damper hooked up to your return duct as well.
    Last edited by Carnak; 08-13-2008 at 12:31 PM.

  12. #25
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,444
    Quote Originally Posted by larobj63 View Post
    Why would you eliminate the ERV? I know the furnace will handle the load - but the ERV still provides a benifit by reducing the load - it's the whole point - constant fresh air with little energy penalty.

    The OP was more concerned with negative pressure issues from intermitant dryer/ range hood use... The ERV is kind of a seperate issue - except, as noted, the air intake of the ERV will "equalize" the building pressure anyhow... Further still - like you said - a small fresh air intake on the return would equalize building pressure - but it's the same energy penalty as a cracked window - which the OP laments.
    My comment was that having a functioning make-up air inlet on the cold air return brings in all the fresh air you need during cold weather or hot weather. You must disable the make-up air inlet during high heating/cooling loads or forget about the ERV.
    Many moderately tight homes during coldest, windy, weather get enough fresh air from natural fresh air ventilation and operation of clothes drier, and kitchen home. Operating the ERV may over-ventilate and cost more money. During the winter weather, excess dryness indicates over-ventilating. I realize that you are tring to do the best you can. Most important to remember, to dry in the winter, stop ventilating. To wet in the summer, get a good dehumidifier. A little complicated. Good Luck TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  13. #26
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by larobj63 View Post
    Why would you eliminate the ERV?
    He sells a product that competes with ERVs

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