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  1. #1

    To zone or not to zone...?

    Dear experts,
    I am seeking for an advise on whether installing multiple heating zones have much sense in my situation.
    At the moment I am planning to convert my house in Massachusetts from electric baseboard heating to natural gas. The house is a typical split entry with 1400 sf main level and 600 sf living space in the basement. The main level is going to be central air (heat pump plus hydroair) and the basement level will be hydronic baseboards. Obviously it gives me two zones already.
    The question is if I will really benefit (cost savings as well as comfort) from setting up two central air zones for the main floor. I am thinking about separating my large (about 600 sf) living room area which has cathedral ceilings and large south facing windows from the 3 bedrooms. Because of the cathedrals and windows in summer the temperature in the living room might easily go to 90F while in bedrooms it stays below 80. Similar in winter cathedrals result in much more volume to be heated.
    When I spoke to contractors in my area they generally advised setting up just a single zone claiming that having two will not make much difference to justify an extra cost.
    I have absolutely no experience with HVAC systems but to me it seems a bit suspicious that a single zone set up (and I assume single thermostat) will be able to efficiently handle such a difference in temperatures. I afraid that in summer my bedrooms will be super-cold trying to keep up with a living room and in winter I'll have same problem but with heating. At the same time I would hate to throw money away on something that I do not really need.

    What are the general principles for making zoning decision? Any recommendations?
    The equipment proposed by contractor is:
    Carrier infinity 2 ton 17 seer 2 stage heat pump; 3 ton infinity variable air handler; 72MBTU hot water coil; 130K BTU high efficient natural gas boiler (also connected to indirect water heater)

  2. #2
    Join Date
    Feb 2010
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    Cal
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    1,596
    Zoning of systems treats comfort issues but you won't realize any savings. Your concerns regarding load diversity is why zoning exists and if room by room load calcs were performed by the contractor, the need should be clear for both parties. If the calcs weren't performed, that might be a red flag. I don't know the carrier model numbers but the greenspeed HP sounds like the perfect fit for your needs, and the infinity method is the best platform for zone control. Retrofitting zoning after the fact doesn't sound like the best way to manage the the project, if that's being considered.

  3. #3
    Join Date
    Jun 2010
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    Mass is going to be a heating load with a Very Modest ( what 800 cooling degree days) so with 2 heating zones already, my thoughts are your 1400 Sf main area is not going to need zone dampers unless you have some mega solar load in one space ( unlikely)

    Save your money
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  4. #4
    Join Date
    Jun 2005
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    SW Wisconsin
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    A 2-stage system would be more compatible with a 2 zone system.

    It ought to be kept in the first-lower-stage when zoned to a smaller area as this would require less CFM airflow, etc. I like the zoning concept as there is no need to cool areas you're not going to be residing in.

    With these new digital programmable thermostats, seems like that could offer some $-Savings, as one could condition each zone to your liking when residing in that zone.

  5. #5
    Join Date
    Jan 2009
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    Keokuk, IA
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    The volume of a room is not as relevant as the surface area. Cathedral ceilings need more heating and cooling because your warm air in winter hangs up at the ceiling. THe main difference is that the walls are larger and you often have larger windows too.

    If air volume was the main driver for heat load, than a 3000 sqft house wit hteh same height ceiling would need 2X the heating and cooling as a 1500sqft home. It doesn't. Not even close. More like only 50% more. The surface area does not increase linerarly with square footage and volume.

    This is why for example a 2 liter bottle of soda, unopened, has a longer shelf life than a 16oz bottle. The CO2 migrates slowly through the Polyethlene. But the surface area to volume ratio of the smaller bottle is greater, so it goes flat faster. Now Once opened, the volume of headspace in the bottle for hte CO2 ot escape into is proportionally greater in the larger vs smalelr bottle.


    Bottom line, as mentioned, you need a proper load calculation done and the ductwork corrected to match the load of each room. If the systme is putting out 1000CFM, and let say 20,000 BTU's of sensible capacity, then if the room with the cathedral ceilings is calculated to need 30% of the load or a 1/2 ton, 6000 BTU's of cooling, then it needs 300 CFM, or more than likely something like 2 8" or 3 6" supplies with maybe 4x14 or 4X10 grills respectively on a system with 7-10 supply registers & branches depending on branch and grill size used. SO a little bathroom might only get a 4 or 5" branch, while a open concept kitchen and dining area might get as many as 4 6" supplies. More supply registers results in mroe even cooling with less hot and cold spots.

  6. #6
    Thank you for explanation.
    motoguy128, if I understood your post correctly with a proper load calculation it is possible and very doable to configure single zone to properly (equally and evenly) heat/cool my house despite cathedral ceilings, orientation, windows, room size etc.
    In such case the only benefit that 2 zones would bring is ability to maintain ant control different temperatures in living room and bedrooms. Correct? Is it the same setup/calculation for heating and cooling?
    One other thing to clarify - several people (including btuhack) mentioned that zoning does not affect the heating cost. I understand that if zones are set to be equal. But with ability to heat/cool zones independently I would expect that by setting up programmable thermostats (as suggested by udarrell) I would be able to save something. In my case we almost never use living area and bedrooms at the same time: bedrooms at night and living area during the day. Any rule of thumb how to roughly estimate practical energy savings from not heating/cooling space when in not in use? Will it be something considerable for my 1400 sf or its so insignificant that not even worth thinking about.

  7. #7
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    You're describing improperly designed zoning mngasmann such as slapping a zone system on an existing system with little thought or modification. This guy is starting from scratch with the intent to do things correctly.

    I think his objective is to determine real world benefits for a job done well.

    Your point is valid and applies to many zoning systems due to poor execution

  8. #8
    Join Date
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    mngasman, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.


    Further infractions may result in loss of posting privileges.
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  9. #9
    Quote Originally Posted by btuhack View Post
    This guy is starting from scratch with the intent to do things correctly.

    I think his objective is to determine real world benefits for a job done well.
    That's exactly what I am trying to do

    Thanks to everybody for great and informative replies. I am very happy that I finally found a place to get real life in depth answers.

    BTW any thoughts on if installing heat pump makes practical sense in my case (instead of just AC). Originally I was proposed hydroair with AC only. But when I found that heat pump is like 5% more to the whole system cost it seemed like a natural option to have as a backup or a hedge against gas prices. I assumed that above freezing temperatures (which is 90% of time lately) heat pump cost should be comparable to a natural gas heat. But contractor was a bit surprised saying that it is not a very usual request - to be fair I also never heard anybody having heat pump here in Massachusetts. So now I am a little bit worried if I am over thinking and throwing money on something that does not make sense or it's more like just a lack of awareness in this area. What do pros think?

  10. #10
    Join Date
    Jan 2009
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    Keokuk, IA
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    Heat pump would be a perfect partner for a hydronic coil because you can use both together and shut down the heat pump based on on fuel costs, not on comfort and maintain very warm temperatures nearly equal to a furnace if done correctly.

    ZOning does not save a significant amount of money.

    IT has the advantage of allowing different termpatures in each zone and compensating for periodic shifts in load such as the sun when mentioned and high occupancy (dinner party & guests) or cooking. How much thsoe imbalances affect your hosue depends on teh home construction. Oen the best things a home can have is thermal mass. That is, materials of construction that are dense and store energy. THsi allows a space ot abosrb heat during short peak periods and slowly release it overtime like a big heat sink. So if your cooking, rather than a space heating up 5F in 20 minutes, it might warm up by only 1-2F, but take 5 tiems longer ot cool back off, but overall its' more comfortable.

    Same with solar gain. I for example don;t ahve much insualtion in my house, but hte exterior is stucco and interior plaster. So the sun has ot heat up hte stucco first, then the air space in the wall, then the plaster inside. As a result, the house heats up slower, but it may take 6-8 hours for it to cool down overnight. THsi was a great feature and done intentionally in 1925 since there was no AC. You cool of hte house in the morning, then clsoe it up, then at night, open it bakc up again. There are also nearly 30" deep eaves that shade the house most of the day.

  11. #11
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    Motoguy is right

    ZOning does not save a significant amount of money.
    But you knew that when you observed
    Will it be something considerable for my 1400 sf or its so insignificant that not even worth thinking about.
    I think you know the answer
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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