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  1. #1

    Newbie question: HRV and positive pressure home

    Hello, first time poster here.

    We are working with a couple of contractors to get a bid to install a HRV system for our house to help drive stagnant air out of the basement. I have several questions.

    1) One contractor suggests that we feed the fresh air supply from HRV into the supply end of our HVAC system, while the other contractor told us that the fresh air from HRV needs to be fed to the HVAC air return so it does not have fight the positive pressure from the powerful HVAC motor to get into the system. I tend to agree with the second contractor. But I would like to check with unbiased Pro's here and see if that makes sense.

    2) We were told that HRV has dampers on both intake and vent ports. We can modulate that to create a positive pressure in the house. That's an ideal solution we are looking for us: keep house air vented, while maintaining positive pressure in the house. We know that during the night and winter when the outside temperature is low, the barometric pressure outside is much higher than that inside the house. My question is: with HRV, can we maintain positive pressure inside house relative to outdoor even at night and in the cold winter (25-40 F).

    BTW, we were told that if we upgrade our fan motor to ECM. The operating cost for ECM and HRV is about $70-$80 a year for electricity ( we understand there will be increased energy bill due to energy escape through HRV system) when we keep system run in continuous mode. Is it true that HRV and ECM only need that energy to operate?

    Thanks

    Alan

  2. #2
    Join Date
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    Quote Originally Posted by AlanT123 View Post
    My question is: with HRV, can we maintain positive pressure inside house relative to outdoor even at night and in the cold winter (25-40 F). This depends entirely on the tightness or leakiness of your home. This can be tested with a blower door during an energy audit which is a good idea.
    • What is your climate? Since moisture infiltration and exfiltration are concerns: Positive pressure is good in the summertime and bad in the winter.
    • Is the "stagnent" air musty and smelling of mildew? If so this is a humidity problem and without control may do serious damage to the very structure of your home. A whole house dehumidifier may be the best solution.
    • Does the proposed HRV have its own fan? If not connecting to the return air is the only option. I don't know why anyone would connect it to the supply ducts, anyway.
    • The ECM for the system fan motor is an excellent efficienct upgrade.
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  3. #3
    Join Date
    Feb 2009
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    To the first question I always run my HRV/ERV systems to the reutrn for that reason and because the air filter on most systems with an ERV is better than the filter in the ERV.

    To the second part what ERV are you looking at and does it have an ECM motor?

    As for upgrading your furnace or air handler to the ECM motor I think realistically it is more like $120 a year in fan costs but this is comoared to about $360 of your current fan if its a 3 ton blower and very minimal additional electric for the ERV depending on how often you run it. You will have some additional heating costs because an ERV only recovers about 86% of the efficiency but this also depends on the model you are selecting.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
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  4. #4
    Quote Originally Posted by lynn comstock View Post
    • What is your climate? Since moisture infiltration and exfiltration are concerns: Positive pressure is good in the summertime and bad in the winter.
    • Is the "stagnent" air musty and smelling of mildew? If so this is a humidity problem and without control may do serious damage to the very structure of your home. A whole house dehumidifier may be the best solution.
    • Does the proposed HRV have its own fan? If not connecting to the return air is the only option. I don't know why anyone would connect it to the supply ducts, anyway.
    • The ECM for the system fan motor is an excellent efficienct upgrade.
    Yes, the HRV has its own fan. It will be used in Pacific NW. Summer is about 65-80F with RH 50%. Winter is about 30-45F ( I don't recall the RH in the winter)

  5. #5
    one more question. The total air volume of the house to be vented is about 28000 cubic feet. What's the minimum size of HRV needed to create a positive air pressure? One of the contractor recommend Carrier HRVCCLHA1250 that provides 177-208 cfm intake flow. Will that be enough?

  6. #6
    Join Date
    Feb 2009
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    Portland OR
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    Typical sizing is based on ASHRAE standard 62.2
    This is volume X 0.85(to account for furniture etc...) so you would be at 23,800
    Next is 23,800 X .35 for the ammount of air changes per hour(3 in this case) so you are now at 8330 and divide by 60 to find the CFM per hour needed. So about 138 CFM per hour. A Lifebreath 155 CFM ECM motor unit may be a good size for your house depending on how it is installed. Where in the PNW are you? I have plenty of recomendations for contractors that I can refer you to or if you are in the Portland Metro area feel free to call me for either consultation or for a quote on home ventilation.

    -Travis
    Owner, Sky Heating & Air Conditioning.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
    Like us on FACEBOOK if you like our advice here!

  7. #7
    SKYHEATING, is the Lifebreath HRV the only HRV on the market with an ECM motor? Is this a good brand/product compared to other HRV's? Its very difficult to identify the "leader", say the top 2 vendors, in this space.

  8. #8
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    Quote Originally Posted by Short Circuit View Post
    SKYHEATING, is the Lifebreath HRV the only HRV on the market with an ECM motor? Is this a good brand/product compared to other HRV's? Its very difficult to identify the "leader", say the top 2 vendors, in this space.
    Well HRV's are rated sometimes in watts per CFM and the life breath is rated at .500 EUI I think only one other brand is close to it. Life breath also makes the units for Honeywell. Panasonic makes a nice spot ventilation fan and VenmaR makes the EKO 1.5 that is incredibly efficient but I have no experience with those.

    The life breath 155 CFM ECM is 72% efficient at32 degrees while the 195 is 85% efficient. The Venmar is 83% efficient at 32 degrees.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
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  9. #9
    SKY, what about HRV's that don't have motors. Passive HRV's. Any thoughts to those? They work when furnace/AC is on, and off when off. The ultimate "green" solution. Very economical as a result, with the negative that it is working when only the HVAC system is working BUT, for fresh air intake, what is your opinion? Ever install any?

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by AlanT123 View Post
    Hello, first time poster here.

    We are working with a couple of contractors to get a bid to install a HRV system for our house to help drive stagnant air out of the basement. I have several questions.

    Thanks

    Alan
    If you want to get rid of the musty basement odor, ventilation without dehumidification will not fix the musty odor problem. I spent 5 years venting basements to eliminate the musty odors. Mold problems got worse in most spaces that had outdoor dew point +55^F. This means ventilation is a solution in arrid climates not green grass climates.
    Get a properly sized whole house dehumidifier. It is a good idea to add a small amount of fresh air to purge indoor pollutants renew oxygen. This will provide <50%RH in the space which will eliminate the musty odors in a couple days. Fresh air is nice via the dehumidifier. Ultra-Air/Santa Fe are good brands and are sponsors of this site.
    If you insist on a HRV/ERV, get a good dehumidifier to keep the space dry. Outside air has to much moisture in most areas to dry a cool space like a basement.
    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"

  11. #11
    Quote Originally Posted by teddy bear View Post
    If you want to get rid of the musty basement odor, ventilation without dehumidification will not fix the musty odor problem. I spent 5 years venting basements to eliminate the musty odors. Mold problems got worse in most spaces that had outdoor dew point +55^F. This means ventilation is a solution in arrid climates not green grass climates.
    Get a properly sized whole house dehumidifier. It is a good idea to add a small amount of fresh air to purge indoor pollutants renew oxygen. This will provide <50%RH in the space which will eliminate the musty odors in a couple days. Fresh air is nice via the dehumidifier. Ultra-Air/Santa Fe are good brands and are sponsors of this site.
    If you insist on a HRV/ERV, get a good dehumidifier to keep the space dry. Outside air has to much moisture in most areas to dry a cool space like a basement.
    Regards TB

    Yes, we do have a dehumidifier running in the basement. It helps. But we need to pull those stagnant air out. Now I am using bathroom fan with window open. lol

  12. #12
    Quote Originally Posted by SkyHeating View Post
    Typical sizing is based on ASHRAE standard 62.2
    This is volume X 0.85(to account for furniture etc...) so you would be at 23,800
    Next is 23,800 X .35 for the ammount of air changes per hour(3 in this case) so you are now at 8330 and divide by 60 to find the CFM per hour needed. So about 138 CFM per hour. A Lifebreath 155 CFM ECM motor unit may be a good size for your house depending on how it is installed. Where in the PNW are you? I have plenty of recomendations for contractors that I can refer you to or if you are in the Portland Metro area feel free to call me for either consultation or for a quote on home ventilation.

    -Travis
    Owner, Sky Heating & Air Conditioning.
    Thanks for running the math for me. Since we will be running HRV in continuous mode, I was told the fan speed with be at 50%. I guess we need to size the HRV motor to be at least 280cfm? Have you been able to create a positive pressurized living space with HRV/ERV ssytem?

  13. #13
    Join Date
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    6,260
    Quote Originally Posted by AlanT123 View Post
    Yes, we do have a dehumidifier running in the basement. It helps. But we need to pull those stagnant air out. Now I am using bathroom fan with window open. lol
    Basements with odors have damp spots. You are not maintaining <50%RH throughout the space. Opening a window will overwhelm standard residieintial dehumidifiers. You need a high capacity unit like the Santa FE which is made to handle 100 cfm of fresh air and maintain <50%RH. You will not have odors with an air change in 5 hours and <50%RH.
    Keep us posted. This is a learning situtuation.
    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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