9′ or 10′ ceiling for mixed humid climate – Zone 4A?
Trying to decide on the best ceiling height for the first floor… 9′ or 10′. I realize 10′ ceiling heights are more expensive from a construction standpoint (more lumber, more labor to cut the lumber since no 10′ studs, more drywall, more insulation, more siding, etc.), but what about the HVAC loads? It would obviously cost more to heat, since heat rises, but how much more? Considerably more or just marginally? I assume it would be cooler in the summer for the same reason? All the older houses around here (before the invention of AC) had 10’+ ceilings as a way to help keep cool. However, they also had radiant heat, which is less of a problem for higher ceilings than forced air.
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Clay,
Higher ceilings increases the surface area of your building envelope, thereby raising your heating and cooling loads.
If you want to lower your heating and cooling loads, however, switching from 10 ft. to 9 ft. ceilings would not be your first choice. There are more important factors -- the air leakage rate through the envelope, window area, etc. So if you want a low-energy house -- try to reduce air leaks, limit the area of your windows, and make sure you have plenty of insulation.
Thanks Martin.
Right, ceiling height isn't first on my list, just wondering how big of a factor it is. I'm zeroing in on insulation levels, air leakage goals, etc, and starting to get down to the final little design tweaks. I guess 10' ceilings also have an additional energy cost in that you usually put bigger windows in a house with taller ceilings to account for the more room.
High ceilings were a pre-mechanical-cooling method of keeping comfortable in the summer. People have been living in hot and humid climates for millennia without AC, and high ceilings are only one of many architecture tricks they came up with to keep comfortable. That said, I think it makes sense to zero in on your actual goal: do you want to rely 100% on mechanical equipment to keep cool, but minimize its use through superinsulation (the modern approach), or do you want to primarily rely on understanding and exploiting the laws of nature to keep cool (the ancient approach)? The reason why it is important to consider this is because these two approaches can be at odds, as Martin demonstrates: 10 foot ceilings increase the size of the building envelope and the volume of interior air, both raising cooling loads from the perspective of a Manual J calculation. If you are going to seal up the house and air condition the entire volume of interior air, 10 foot ceilings will raise your AC bills. But what this sterile calculation doesn't take into account, however, is comfort. 10-foot ceilings and ceiling fans may allow you to feel comfortable when the temperature of the air 5 feet off the ground is 80 degrees. So your house may actually gain more heat then a lower-ceilinged house, but you will feel more comfortable because that heat will be concentrated above your head. Air movement from opening the windows and running your ceiling fans will help with comfort in the high humidity and prevent mold growth, and you won't have to pay such critical attention to air sealing. The few times when it becomes overwhelming would call for a cheap window AC unit that you won't have to run for very long, and that you can easily replace yourself if it malfunctions.
Is this approach superior to having 8 foot ceilings, a superinsulated airtight building envelope, high-performance windows you never open, and a high-efficiency mini-split heat pump? You'll have to answer that question for yourself. The modern, high-tech building science approach will probably yield more comfort, but it requires a considerably higher standard of construction that many contractors have difficulty with, and it results in total reliance on expensive built-in mechanical equipment that ties the homeowner to repair and maintenance techs forever. And it's more expensive. Of course the exact climate matters; if the relative humidity is 100% for 6 months out of the year, maybe you'll want to go the building science route and never look back. :)
Thanks Nate G.
I guess that is the dilemma. I was raised in the country in an old house with high-ish ceilings, large shade trees completely covering the yard, and a whole-house fan as our only means of cooling in the summers. We had an A/C, but never used it because we were able to get by with the natural cooling of the trees and the fan.
We are building this house out in the country as well, so we will also have the advantage of cooler temps away from the heat island effects. What we won't have is lots of shade, at least for many years. The house will sit up on a hill, though, and gets a great breeze (even yesterday when it was 90+, standing under the lone shade tree on the hill was very pleasant). I can foresee us opening the windows and bringing in the fresh for a couple of months out of the year. Spring and Fall in KY is very comfortable, especially in the country.
However, I have a wife that has a very thin margin of comfort. I don't know if she is cold blooded or what, but she can go from being too hot to too cold within just a few degrees. When it is time to close up the windows and go mechanical, it needs to work.
Delete.