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Thread: Hrv Erv ?

  1. #1
    Join Date
    Jun 2008
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    Hrv Erv ?

    Im in the process of building a new house

    2 story 2500 sq ft.

    We are using spray foam insulation and it is set up with a 2 heat pumps and 2 back up furnace one for upstairs one for down stairs. With that being said the house is going to be real tight and need a source of fresh air. With that being said. Will an HRV with a capacity of 3000 sq ft home work if I only have it hooked up to the downstairs system. Thanks for the replies.

  2. #2
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    Jun 2003
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    What part of the country do you live in? Better question might be exhaust, make-up, or balance flow ventilation. 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"

  3. #3
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    Jun 2008
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    I live right out side of St. Louis MO.

    I'm thinking this is going to be a balance setup. What ever comes in goes out.

  4. #4
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    Quote Originally Posted by acnoob1 View Post
    I live right out side of St. Louis MO.

    I'm thinking this is going to be a balance setup. What ever comes in goes out.
    Clothes drier, bath fans, kitchen hood, and combustion make-up air should also be considered. For IAQ also consider keeping the summer humidity <50%RH while getting your 50-75 cfm of fresh air? Think about a ventilating whole house dehumidifier as also an option.More later. 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"

  5. #5
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    Lancaster PA
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    67,778
    You would be better off with a ERV, then a HRV.
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  6. #6
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    Jun 2008
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    Well I was debating the fact. We are right on the bubble of HRV/ERV. I was looking at the Fantech HRV/ERV's from what I was told I can by the ERV Core and in the summer time change it then when winter rolls around plug in the HRV core. NO?

  7. #7
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    Your probably better off with an ERV summer and winter.
    Why do you want to use a HRV to bring humidity in the house in the summer?
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  8. #8
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    i wanted to go erv but was told since we were in the middle the HRV would be better suited. But like you I want as much of the humidity gone in the summer, That is why im here trying to figure this out since, it seems some of the sales guys do not know what is going on. Thank you for the advice.

  9. #9
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    You have many exhaust devices in your home that need make-up air to function. The bathfans, clothes drier, kitchen hood, and water heater need make-up air. ERV is a balance flow device that does not supply make-up air. During wet outside conditions, an ERV brings in moisture. About half of the outside moisture makes it through the ERV along as dry air is exhausted. If you plan on a air change every 4 hours, you are still introducing 2 lbs. of moisture an hour. Plan on some supplemental dehumidification even with an ERV. Plus the make-up air that your exhaust devices need adds up to many lbs. of moisture that must be removed everyday during damp days in green grass climates. ERVs are expensive but do save energy, about $150/year. For about the same investment, a whole house ventilating will provide fresh year around make-up air ventilation for your exhaust devices, for your family IAQ, and maintain <50%RH during wet cool weather. Very comfortable and healthy. If you can afford both, great. With an ERV you should have a 90 pint per day dehumdifier. I consider the whole house dehu primary. Now is the time to investigate both. If you go with the ERV, monitor your indoor %RH, particularly in the lower levels of the home. Check my other post for more discussion if interested. 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"

  10. #10
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    Jun 2008
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    TB, So, here is question. If I have the contractor run the exhaust vents outside the house via the roof or a wall and add some time up make up air setup to the hvac system. Would this work. Or am I missing something. Thanks for the help

    RS

  11. #11
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    Quote Originally Posted by acnoob1 View Post
    TB, So, here is question. If I have the contractor run the exhaust vents outside the house via the roof or a wall and add some time up make up air setup to the hvac system. Would this work. Or am I missing something. Thanks for the help

    RS
    From the stand point of the exhaust devices operating, yes, this about all you can do. Unfortunately, a clothes drier needs 150 cfm of make-up air to operate. Bath fans need 75 cfm. Kitchen hoods need 150 cfm. Occasionally, a couple of these device operate at the same time. Putting a 6" make-up air inlet on a cold air return only brings fresh air when the blower is operating, 75-100 cfm. When the blower is off, the only air coming in is from the negative pressure created in the home. This might be 10 cfm. The rest of the need make-up air is sucked in through any open chiminey or imperfection in the structure. Easy to understand why to avoid any open combustion devices fireplaces, water heater etc. Equip your the home with power exhaust heaters. You have to live with the negative pressure. Using a ERV/HRV is not ideal because they exhaust as much air as they introduce. Better to use make-up air ventilation.
    A bigger problem is making sure you get enough fresh air to purge indoor pollutants and renew oxygen for your family. Most experts suggest a minimum 75 cfm during occupancy for a home your size. In your climate, the fresh make-up air will keep the home from being too humid during cold weather. The dry outside air will remove the moisture generated by the occupants. But during the spring, summer, and fall, the much need fresh air has excess moisture that wets the home. During peak cooling hours, your a/c will remove the 60-80 lbs. of moisture per day. That the amount of moisture is from the fresh air and occupants. On cool evenings and wet cool days, the a/c does not run enough to provide the dehumidification. American Medical Ass., American Lung Ass., EPA suggest maintaining <50%RH to avoid mold/dust mites and for comfort.
    I was using fresh air ventilation in client's homesduring the late 80s and had warm weather moisture problems. By incorporating fresh make-up air ventilation with a dehumidifier, we have managed to provide fresh air when the home is occupied, maintained <50% outdoor moisture is high and there is low/no a/c load.
    Since many have followed suit. Check out ventilating whole dehumidifier as a method of providing make-up fresh air for your exhaust appliances while maintaining <50%RH. You can set-up your a/c when you are not home while maintaining <50%RH. This reduces energy cost. There will be comments and question, I am sure. I am attaching data from my home illistrating partial load conditions. Sorry to drag you so far. Regards TB
    Attached Images Attached Images  
    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"

  12. #12
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    Jun 2008
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    58
    TB,

    Thanks for the info, now that my head is spinning

    So let me try to take this from the top.

    Since Im going to be using a spray foam with good windows, The house should be if done correctly very tight.

    Since it is tight, The appliances listed below need some type of air coming into the house to have them operate correctly.

    If I install some type of make up air system it will only function when the hvac system is running.

    With that being said what else is my option I thought I checked out the thermastor ultra aire. Is this what you are talking about for make up air. but doesnt this just give me dehumidified air to run threw the HVAC system. So it would not be effective unless running the hvac fan.

    The only gas appliance I have is a sealed fire place and the hot water tank. With the hot water tank are you suggesting I add some type of forced air vent.

    If Im off base sorry, Im a slow learner.

    rs

  13. #13
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    Quote Originally Posted by acnoob1 View Post
    TB,

    So let me try to take this from the top.

    Since Im going to be using a spray foam with good windows, The house should be if done correctly very tight.

    Since it is tight, The appliances listed below need some type of air coming into the house to have them operate correctly.

    If I install some type of make up air system it will only function when the hvac system is running.

    With that being said what else is my option I thought I checked out the thermastor ultra aire. Is this what you are talking about for make up air. but doesnt this just give me dehumidified air to run threw the HVAC system. So it would not be effective unless running the hvac fan.

    The only gas appliance I have is a sealed fire place and the hot water tank. With the hot water tank are you suggesting I add some type of forced air vent.
    rs
    Thanks for allowing me to explain the concept. Most a/c contractors have not attempted to use this new concept yet. They are attempting to avoid fresh air and using full featured a/c systems to provide comfort.
    UA has the option of being your make-up ventilating device. The fresh air is duct to the UA. The UA mixes the desire amount of fresh with the air in your home. The UA filters and supplies air to supply side of your a/c for distribution throughout the home. The UA has an occupancy timer that provides make-up air when you are routinely in your home. The amount of fresh air is adjustable. So make-up air when and as much as you want. When the indoor %RH rises above the desired level (<50%RH), the dehu is activated. All of this without any a/c/furnace operation. As your typical exhaust appliances are operated when you are in your home, make-up air available to aid their operation. Hot water tanks should be power exhaust to avoid any possibility of back-drafting. The cost of UA is a little more than a ERV. You will have fresh make-up air, humidity control, and a simple system without interaction of the other systems in your home. I will attach my daily data graph showing 14 hours of fresh air during occupancy and the a/c cycle later. You will notice the humidity levels throughout the home. I just started up the ventilation system and am fine tuning it. I do not any graphs will rainy cool weather like you have today. Fresh make-up weather during cool weather is the greatest challange. I use 7kw/day on the dehu and 15-18 kw/day on the a/c. you should do better with your new home. 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"

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