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  1. #1
    Join Date
    Jul 2012
    Posts
    48

    Zoned HVAC System vs Single Zone and Heated Basement Floors

    Hi,

    I am looking at purchasing a new house. To my dismay it is not a zoned system, which is the only issue I have with it. It was something I was really hoping for since our current home has different temperatures on the main / upper and basement floors.

    The house we are looking at is about 3000sq ft. All the basement floors have radiant hot-water heat.

    When we arrived at the home, it was quite cold in the basement (not surprising considering the A/C was on - have the same problem at my current home). My question is two-fold:

    1. Even with a zoned system, when the A/C is on at the upper floors, will the cold air "drop" to the basement causing the basement to be very cold? (So, what I am getting at is even if we do have a zoned system, during the summer when the A/C is used, will the basement be freezing regardless?)

    2. Will turning on the basement in-floor heating when the A/C is on result in huge energy waste? I would just like it to be comfortable down there as we plan on using it as a movie room...

    3. In the winter during heating season, is it more economical to turn the radiant floor heat up a few degrees higher than the furnace setting so that some of the basement heat will creep upstairs? (e.g., is radiant floor heating more efficient than a 95%+ natural gas furnace)?

    Thanks!

  2. #2
    Join Date
    Mar 2010
    Location
    NJ
    Posts
    327
    1. Cold air will migrate to lower levels. Zoning will not completely solve this problem.

    2. I imagine that the utility company will be very happy, but you won't be.

    3. Radiant will be more comfortable. Efficiency and energy usage will really depend on your exact conditions and run times.

    I think your best first step will be to assess the construction of the basement. Make sure it is well insulated. Invest in a good carpet to minimize the effect of cold floors.
    ecuacool
    732-494-HELP
    http://ecuacool.com

    Guaranteed energy savings.
    Serving all of NJ, NYC, and eastern PA.

  3. #3
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by JStar View Post
    1. Cold air will migrate to lower levels. Zoning will not completely solve this problem.

    2. I imagine that the utility company will be very happy, but you won't be.

    3. Radiant will be more comfortable. Efficiency and energy usage will really depend on your exact conditions and run times.

    I think your best first step will be to assess the construction of the basement. Make sure it is well insulated. Invest in a good carpet to minimize the effect of cold floors.
    Carpet over the radiant is not a good idea.

  4. #4
    Join Date
    Mar 2010
    Location
    NJ
    Posts
    327
    Quote Originally Posted by second opinion View Post
    Carpet over the radiant is not a good idea.
    You can use a thin carpet, with a rubber pad. The heat transfer will be cut down a little, but a new carpet is easier, and less expensive than redesigning an entire system.
    ecuacool
    732-494-HELP
    http://ecuacool.com

    Guaranteed energy savings.
    Serving all of NJ, NYC, and eastern PA.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Lower floors are colder for 2 reason. 1) Convection, cooler denser air falls and warm air rises. 2) Stack Effect & Reverse stack effect. The temperature differential between indoors and outdoors creates a difference in air pressure. (like in a hot air baloon) Cool air is more dense and therefore has more pressure. IN summer cool air pushes out air leaks on lower floors and hot humid air leaks into upper floors. IN winter cold dry air leaks in downstairs and warm humid indoor air leak upstairs.

    DEpending on your homes layout, Stack effect can be a stronger than convection which is often easily broken by stratificaion of air at the ceiling

  6. #6
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,739
    3: duct leakage (should probably be #1)
    4: oversized equipment.
    5: enclosure leakage (building envelope)

    Search aeroseal to see the effect of duct leakage on temperature differential across floors.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,737
    I did a 3 zone system (a thermostat on every level) for a doctor's newly constructed home.

    He had a situation as yours, except he did not have the basement in floor heating.

    He would set the basement stat to "take the chill" out of the basement when he/they were down there.

    To keep the A/C from "falling" to the basement I would insulate all of the ductwork.

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,535
    Insulate the ducts is a fix for the cold basements. If the basement is finished, recirculating the air throughout the home uses the basements cool air to cool the home during the off cycle.
    Also basements tend to have high %RH and require a dehumidifier which will lower the %RH while adding a couple degrees to the basement temp.
    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"

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    I'd suggest you consider a mini-split heat pump to provide much better options for the basement than trying to modify the existing system or running the radiant floor heat.

    Radiant floor heating is a great solution for cold floors (masonry) or even wood floors in the dead of winter. Great comfort, consistent heat, all for which you could ask. But for short heat bursts, as in the shoulder months, radiant sucks. It's way too slow to respond to a desire to warm the area for a 2-hour movie in the evening and heating all summer is a waste of energy.

    The mini-split heat pump will solve that entire problem, as well as provide you with dehumidification when cooling is not needed. It will heat the space quickly when you want to pre-heat for the movie, then will automatically (if set to auto) begin to cool when the warm human bodies and movie equipment are all present in the small area. If it's just too humid, select 'dehumidify' mode and let it rip. When the movie's over and you're all gone upstairs, have it programmed to automatically maintain a different temperature (higher or lower, your choice) or manually select it "off" until you want to use it again. This is the environment and parameters where a mini-split just can't be beaten. No other solution will give you the heat/cool/dehumidify options of the heat pump. Then when winter arrives, turn the HP off and let the radiant floor do the job. Voila, comfort in all seasons.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  10. #10
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,739
    Quote Originally Posted by George2 View Post

    To keep the A/C from "falling" to the basement I would insulate all of the ductwork.
    Nuts George, that's a big one.

    6. Insulate ductwork.

    My mother turns her furnace fan to continuous in spring to combat cold basement. The ground tends to be very cold, and ther is little call on the equipment.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,535
    Quote Originally Posted by skippedover View Post
    The mini-split heat pump will solve that entire problem, as well as provide you with dehumidification when cooling is not needed. It will heat the space quickly when you want to pre-heat for the movie, then will automatically (if set to auto) begin to cool when the warm human bodies and movie equipment are all present in the small area. If it's just too humid, select 'dehumidify' mode and let it rip. When the movie's over and you're all gone upstairs, have it programmed to automatically maintain a different temperature (higher or lower, your choice) or manually select it "off" until you want to use it again. . Voila, comfort in all seasons.
    How about a description of how the minisplit dehumidifies a cool damp area?
    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"

  12. #12
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,737
    Quote Originally Posted by tedkidd View Post
    Nuts George, that's a big one.

    6. Insulate ductwork.

    My mother turns her furnace fan to continuous in spring to combat cold basement. The ground tends to be very cold, and ther is little call on the equipment.
    I think that deserves a thank you, if I read it correctly?

  13. #13
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Quote Originally Posted by teddy bear View Post
    How about a description of how the minisplit dehumidifies a cool damp area?
    Regards TB
    Sure. With the wireless control, select 'dehumidify'. the indoor blower slows dramatically, just enough to keep the coil from freezing and the TD widens dramatically. Just like a regular humidifier. That's why it's manually selected and why they call it 'dehumidify' mode. Just like any other dehumidifier, there will be some slight cooling effect but it's normally minimal. Otherwise, if the air is already cool, we call that a heating situation. Raising the temperature of the room without adding moisture will lower the relative humidity. Them's the laws of physics at work.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

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