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  1. #1
    Join Date
    Feb 2013
    Posts
    15

    Big house air exchange ?

    We just bought a new (to us) house in Calgary, Alberta. Its a 2 story, built in 2007, 5,000 ft^2 finished, including the basement, 9 foot ceilings throughout.

    Its appears to be a very well built home. Its probably pretty air tight.

    The house has an on demand natural gas hot water heater and hot water storage tank feeding heat exchange coils in dual forced air heat exchange units, one for the main floor and one for upstairs. The basement has its own recirculation fan and ducting and in floor hot water heat coils. The house also has dual AC.

    4 to 6 people live in the house at any one time.

    I'm concerned about how much air moves in the house. I estimate the volume of the house to be about 52,000 ft^3. (52 x 37 x 9 x 3) Given a recommended air change rate of 5 per hour, that leads to a ventilation rate of 4300+ CFM.

    The house has no where near that much air movement. The only "normal" ventilation that I am aware of is
    - bathroom fans in 5 bathrooms, which are generally never on
    - natural gas stove hood vent, which is not usually on
    - leakage from the flue on the natural gas fireplace
    - 1 clothes dryer vent
    - the hot water heater is high efficiency and uses PVC piping for the exhaust to a vent on the side of the house.

    The builder also installed some sort of booster recirculation fan system. There is a switch on the main floor. You turn it on and you hear a louder fan noise and the air flow from the vents increases dramatically. The current owner says it great in the summer time and it keeps the house very fresh.

    The house does not use conventional rectangular air vents for the supply to the rooms. It uses small, round (2" diameter) vents and a lot more of them. They seem to move a decent amount of air normally and a lot of air when the booster fan is turned on.

    We currently live in a similar sized house to the one we bought. It has a big, noisy, bathroom style ventilation fan in the ceiling on the upper floor controlled by a switch on the main floor. When the air in our current house feels stale or is smelly because of cooking (down draft natural gas cook top built into the island, no vent hood) we turn it on. Having done that, the air in our current house always seems a bit stale. The new house has no such fan set up.

    We are about to do some renos in our new house prior to moving into it.

    What changes, if any, would you make to the air ventilation system on this house ?

    Given that we live in a cold climate and the volume of air a house like this seems to need, would you install an air to air heat exchanger so that the ventilation rate can be kept up without spending a lot on heating the incoming air ?

    Thanks !

  2. #2
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,761
    To get an idea of what is needed, you really need to know what you've already got, as far as air change is concerned. It would be worth it to get an idea of just how much 'natural leakage' the home has, and figure out if it is enough to keep the air fresh, or if it would be better to try to seal it up and run a controlled amount of fresh air through a heat recovering ventilator. I've always been a fan of the idea of running an ERV ducted from each 'dirty' space in the home. Each bathroom, mudroom, laundry, and kitchen. The 'Fan' switch in each bathroom would turn it on, for on-demand use, effectively ventilating all spaces when on, and then also have a minimum amount of time a day where it is forced to run, as determined by the desired air change.

    Of course, if the house has enough natural leakage, none of that may be required. However, there are energy and cleanliness benefits to sealing up all the 'uncontrolled' leaks, and replacing it with a heat-recovered, and filtered, fresh air system.

  3. #3
    Are the Dual Air conditioning units and the Forced Air heating unit you speak about using the same blower section? The Dual Air Conditioning Unit or Heating Unit is suposed to be designed with a certain percentage of outside air usually introduced into the return air prior to the filters. You can look in the return air section and see if there is a duct of some kind that goes directly to the outside, usually through the roof with a vent cap on a pipe. It will not be a very large size duct, and is usually round in residential applications. When the A/C or heating blower unit is running is when you should get the most air movement or air exchange. I would be interested to know the name brand and model and serial numbers of your HVAC/Heating units. Occasionally units are designed for a particular size square footage home and the designer does not take into consideration the extra foot hight in the ceiling. This could lead to an HVAC system that is undersized. But without all the information it would be hard to make a determination and it would be only an estimate without doing a proper load calculation of your home.

  4. #4
    Join Date
    Feb 2013
    Posts
    15
    Quote Originally Posted by CraziFuzzy View Post
    To get an idea of what is needed, you really need to know what you've already got, as far as air change is concerned. It would be worth it to get an idea of just how much 'natural leakage' the home has, and figure out if it is enough to keep the air fresh, or if it would be better to try to seal it up and run a controlled amount of fresh air through a heat recovering ventilator. I've always been a fan of the idea of running an ERV ducted from each 'dirty' space in the home. Each bathroom, mudroom, laundry, and kitchen. The 'Fan' switch in each bathroom would turn it on, for on-demand use, effectively ventilating all spaces when on, and then also have a minimum amount of time a day where it is forced to run, as determined by the desired air change.
    I'm a fan of those systems too. My uncle has it in his house. However, it would be nearly impossible to retrofit that into our new house.

  5. #5
    Join Date
    Feb 2013
    Posts
    15
    Quote Originally Posted by geopat89 View Post
    Are the Dual Air conditioning units and the Forced Air heating unit you speak about using the same blower section?
    Yes, in both the house we currently live in and the new house. The new house has the booster fan setup, our current house doesn't.

    The Dual Air Conditioning Unit or Heating Unit is suposed to be designed with a certain percentage of outside air usually introduced into the return air prior to the filters. You can look in the return air section and see if there is a duct of some kind that goes directly to the outside, usually through the roof with a vent cap on a pipe. It will not be a very large size duct, and is usually round in residential applications. When the A/C or heating blower unit is running is when you should get the most air movement or air exchange.
    The HVAC room is in the basement on both of these houses. The current house has a 10 inch round insulated flexible duct connected to a standard 4" outside vent to supply "make up" air.

    I would be interested to know the name brand and model and serial numbers of your HVAC/Heating units.
    The current house has twin Lennox Elite G51 MP furnaces.

    Occasionally units are designed for a particular size square footage home and the designer does not take into consideration the extra foot hight in the ceiling. This could lead to an HVAC system that is undersized. But without all the information it would be hard to make a determination and it would be only an estimate without doing a proper load calculation of your home.
    Heating wise the furnaces seem to have plenty of capacity. The house is never cold.

    Cooling wise, there were issues with the basement being freezing and the rest of the house hot and stuff. I fixed that by taping all the air leaks in the ducting in the HVAC room. Then it was pretty good.

  6. #6
    Join Date
    Feb 2013
    Posts
    15
    I'm concerned about how much air moves in the house. I estimate the volume of the house to be about 52,000 ft^3. (52 x 37 x 9 x 3) Given a recommended air change rate of 5 per hour, that leads to a ventilation rate of 4300+ CFM.
    It turns out that a house needs way less than 5 air changes per hour. More like 0.3.

    The required ventilation rate is then 52,000 ft^3 x 0.3 = 260 CFM.

    I'm thinking of installing 2 VHR units, one for each floor. Each floor has its own air return.

  7. #7
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    961
    Quote Originally Posted by BigBear23 View Post
    We just bought a new (to us) house in Calgary, Alberta. Its a 2 story, built in 2007, 5,000 ft^2 finished, including the basement, 9 foot ceilings throughout.

    The house does not use conventional rectangular air vents for the supply to the rooms. It uses small, round (2" diameter) vents and a lot more of them. They seem to move a decent amount of air normally and a lot of air when the booster fan is turned on.

    Thanks !
    I'm thinking because of the ceiling heights and the 2" supply vents this sounds like it designed as a high static, high volume. This pushes the air through smaller duct and pushes air down. They may have used this design so they could get the height of the ceiling and ease to run ducts throughout the house. Smaller ducts are easier to run and take up less room.. I would verify the design intent. any changes to the duct that may change static and volume will effect the whole system.

  8. #8
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,735
    Check out www.comfortinstitute.org and www.bpi.org to get the infiltration measured.
    Heating/Cooling Services Inc.
    www.andersonhvacservice.com

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,338
    My bet is that this house get an air change in 4-5 hours during cold windy weather. Therefore, no fresh air ventilation is needed on cold windy days. You will need 3-5 lbs. of humidification during these days. Adding any mechanical ventilation during cold windy weather will increase your humidification needs and over ventilate the home.
    Also consider that you need mechanical fresh air ventilation during mild calm weather and the home is occupied. Move into this home and operate your humidification. If the home is overhumidified, consider ERV/HRV.
    You are getting way ahead of yourself. No need for more than 150 cfm of mechanical fresh air anytime. This added to the natural and is more than enough.
    Regard 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
    Quote Originally Posted by BigBear23 View Post
    We just bought a new (to us) house in Calgary, Alberta. Its a 2 story, built in 2007, 5,000 ft^2 finished, including the basement, 9 foot ceilings throughout.

    Its appears to be a very well built home. Its probably pretty air tight.

    The house has an on demand natural gas hot water heater and hot water storage tank feeding heat exchange coils in dual forced air heat exchange units, one for the main floor and one for upstairs. The basement has its own recirculation fan and ducting and in floor hot water heat coils. The house also has dual AC.

    4 to 6 people live in the house at any one time.

    I'm concerned about how much air moves in the house. I estimate the volume of the house to be about 52,000 ft^3. (52 x 37 x 9 x 3) Given a recommended air change rate of 5 per hour, that leads to a ventilation rate of 4300+ CFM.

    The house has no where near that much air movement. The only "normal" ventilation that I am aware of is
    - bathroom fans in 5 bathrooms, which are generally never on
    - natural gas stove hood vent, which is not usually on
    - leakage from the flue on the natural gas fireplace
    - 1 clothes dryer vent
    - the hot water heater is high efficiency and uses PVC piping for the exhaust to a vent on the side of the house.

    The builder also installed some sort of booster recirculation fan system. There is a switch on the main floor. You turn it on and you hear a louder fan noise and the air flow from the vents increases dramatically. The current owner says it great in the summer time and it keeps the house very fresh.

    The house does not use conventional rectangular air vents for the supply to the rooms. It uses small, round (2" diameter) vents and a lot more of them. They seem to move a decent amount of air normally and a lot of air when the booster fan is turned on.

    We currently live in a similar sized house to the one we bought. It has a big, noisy, bathroom style ventilation fan in the ceiling on the upper floor controlled by a switch on the main floor. When the air in our current house feels stale or is smelly because of cooking (down draft natural gas cook top built into the island, no vent hood) we turn it on. Having done that, the air in our current house always seems a bit stale. The new house has no such fan set up.

    We are about to do some renos in our new house prior to moving into it.

    What changes, if any, would you make to the air ventilation system on this house ?

    Given that we live in a cold climate and the volume of air a house like this seems to need, would you install an air to air heat exchanger so that the ventilation rate can be kept up without spending a lot on heating the incoming air ?

    Thanks !
    How old is the flexible ducting in your house? Make sure that it is in good condition, especially since you have a big house, if the air flow has any blockage it can get very hot or cold depending on the season. In my house the downstairs gets very hot in the summer and cold in the winter because of the way the venting is set up. I would also have a HVAC worker examine the house to give you an in-person professional opinion.

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