Do I really need to cool the whole house all the time?

There are inherent benefits to cooling the whole house including better air circulation, filtration and the elimination of cold or hot spots. However, there are times when cooling the upstairs bedrooms don’t make sense if no one is sleeping in them.  There are two real options to successfully zoning your cooling space.  The first is to invest in a second air conditioner and have one cool the most active space and the second be on ‘standby’ for the lesser used space.  This requires the rerouting of your duct work but can provide additional controls for times when both spaces are used.  The second option is to use a high efficiency system which can provide cooling modulation to adapt its power output based on which zones need to be cooled. Because the high efficiency systems are able to throttle up or down they are able to maintain humidity control and air flow and thus, overall air quality and comfort won’t be negatively affected.  If you try to shut off rooms with a single, lower efficiency, fixed capacity system it can lead to moisture/humidity problems as well as spikes in temperature to make you uncomfortable.  You could also severely damage the system if you shut off too many vents.  Zoning is an excellent way to save on energy costs, but your contractor should help you select the right equipment to support that approach.

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5 thoughts on “Do I really need to cool the whole house all the time?

  1. My house has 2 AC SEER 12 for 15 years. One is only work at night so it’s still good, another looks not efficiencely. I plan to replace it . I wonder I have to replace the 2 AC same time or replacement one first.

    Thanks!

    • You should not have to replace both units. I also suggest just replacing the one that has the most run hours if you are concerned about it. However, I would have them both checked out first to see if they both might run a few more years though. Typically HVAC systems are replaced on average at 14 to 16 years of age depending on run time and whether they are heat pumps – running year round. Some last a lot longer. I would get someone to look at it and get a few opinions before spending money on replacing it. I hope this helps to answer some of your questions.

  2. I have a cape plan and the upstairs is too hot in the winter and not cool enough in the summer. One split HP system, A/H located in the garage. Has a RA upstairs at the top of the steps and one RA on the first floor in the living room, but the main one is at the AH plenum. Is there a way to install a turning vane in the duct going upstairs to balance the amount of air, or do I also need to adjust the fan?

    • Plenum dampers would be one option to distribute the conditioned air more effectively and some of these are available on the market or through your HVAC contractor. Adding a variable speed or staged indoor air handler might also help, or maybe a contractor could adjust the one you have to provide more air flow. Ceiling fans are another way to improve air distribution. When you decide to replace this system we’d recommend having the contractor check your required capacity because it might be undersized for extreme temperatures – both hot and cold. We also recommend a 16 SEER or higher system with at least two steps of capacity modulation to allow your system to keep you comfortable on those extreme days but also provide enough run time on more moderate days. Two capacity steps or variable speed capacity is not only more efficient it also prevents problems with humidity or long “off cycle” periods which might cause other problems.

  3. This article was very helpful, I always shut off vents in the rooms that aren’t used as often but it often makes the other rooms either really cold or humid. Zoning sounds like a good option.

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