9' ceiling vs 10' ceiling and cooling costs? (Phoenix, Tempe: new house, homebuyer)

[HX_Guy]

What is the general consensus on flat 9' tall ceiling vs 10' tall ceilings and how it affects energy costs?

I would think that 9' would cost noticeably less because you have that much less space to cool, so it's more efficient. But then with 10' ceilings, the heat can rise more and you could possible not feel as hot, therefore keeping the thermostat at a higher temperature?

[Jkgourmet]

I wouldn't consider the cost of heating and cooling as much as I'd consider the consumer preference for 10' ceilings affecting your eventual resale value. To say nothing of your personal enjoyment of your home.

[nightgirl151]

Our old house had 9' ceilings, our new house has 10' ceilings. Our electric bill is noticeably higher at the new house, and overall the house feels warmer with the higher ceilings (about20% higher) When the air is on, even standing under the vents I can barely feel the cooler air vs at the old house you could definitely feel the cool air with lower ceilings. That being said, our bill is higher but we went from a 1700 sq ft house to a 2200 sqft house, and changed from SRP to APS territory, and APS rates are higher as well.

The house with ten foot ceilings was built in 2010, does not have radiant barrier, but we did add additional insulation to the attic which had r30, now is r43. We also have shade screens on all windows, and lots of tile in house.

[Zippyman]

I'd be really surprised if ceiling height made a noticable difference - air leakage & poor insulation are the biggest factors for cooling costs, neither one should be an issue in a new home.

[HX_Guy]

I see it like this...2,900 sq ft house with 9' ceilings is 26,100 cu. ft. that need to be cooled, vs if it had 10' ceilings, it would be 29,000 cu. ft, so right about 11% more space to cool. Wouldn't that take 11% more energy or is it not that simple and straight forward?

[wit-nit]

Originally Posted by HX_Guy

I see it like this...2,900 sq ft house with 9' ceilings is 26,100 cu. ft. that need to be cooled, vs if it had 10' ceilings, it would be 29,000 cu. ft, so right about 11% more space to cool. Wouldn't that take 11% more energy or is it not that simple and straight forward?

You are correct, the variance would be 10-11% more in cooling costs. Since heat rises the heating cost increase would probably be very minimal, probably 3-5%.

[dualforecast]

good ceiling fans, that run slowly may give you more no a/c days with the higher ceiling.

[Zippyman]

Originally Posted by HX_Guy

I see it like this...2,900 sq ft house with 9' ceilings is 26,100 cu. ft. that need to be cooled, vs if it had 10' ceilings, it would be 29,000 cu. ft, so right about 11% more space to cool. Wouldn't that take 11% more energy or is it not that simple and straight forward?

You can drive yourself batty trying to do the calcs for energy usage - and in the end, much of what you will calculate is "perfect world" stuff. When you're talking about hvac, especially here in the desert, theres a tremendous amount of garbage info out there from people with an agenda, even our own government! Seer ratings are a perfect example - 90% of the "weight" of that rating is derived at (outdoor) temperatures below 90 degrees. What that means in the real world is that an 18 seer unit is super efficient at 75 degrees, and not much different than a 14 seer unit at 100 degrees. Back east, where they have humidity, and run the a/c when the outdoor temps are 80, they save a lot of juice with high-seer units. Out here, the math doesnt work, and the savings from a higher seer-rating (at the real-world temps we experience) is a nothingburger, with a side of nothing.

To more directly answer your question, about 30% of heat loss (not gain) is through your walls. About half of that 30% loss is through your windows.. possibly more, if your window installer was hung over, or lazy. So the calculation of wall area loss isnt a straight-line, unless you're adding window area along with wall area. And heat loss calcs are different than heat-gain calcs, so ymmv.. to be honest, I havent found much reliable info out there on the web.

There is some software that hvac guys & engineers use to calculate expected heat loss/gain, ("manual d" to calculate ductwork, and "manual j" to determine the necessary size for a hvac system in btu's), but even with that, it's based on some assumptions that are not likely to fit your circumstances (there's an assumed "set point" for your thermostat - if you read a few posts here on c-d, you'll see some people in Phoenix think 85 is comfortable, and others who begin sweating profusely @ 70 degrees.. ).. that fact alone could give you a horribly under/oversized hvac system, - and given a choice, your builder is going to pick an oversized system, because no one complains when the a/c delivers a blast of cold for three minutes, then shuts down.. ( even though that wastes a tremendous amount of energy)..

An interesting read..

http://www.ag.ndsu.edu/extension-abe...les/epq072.pdf

And another interesting link:
http://www.energyvanguard.com/blog-b...d-HVAC-Systems

[PaulieM]

Originally Posted by HX_Guy

I see it like this...2,900 sq ft house with 9' ceilings is 26,100 cu. ft. that need to be cooled, vs if it had 10' ceilings, it would be 29,000 cu. ft, so right about 11% more space to cool. Wouldn't that take 11% more energy or is it not that simple and straight forward?

It is that simple and straight forward. The mere fact that you raise this issue reveals the growing trend of homebuyers to look at the space in terms of volume. In your case that extra 2,900 cu.ft. pencils out to an 18X18 sq.ft w/9ft. ceilings room that you don't get to use but you're paying to condition.

[Zippyman]

Originally Posted by PaulieM

It is that simple and straight forward. The mere fact that you raise this issue reveals the growing trend of homebuyers to look at the space in terms of volume. In your case that extra 2,900 cu.ft. pencils out to an 18X18 sq.ft w/9ft. ceilings room that you don't get to use but you're paying to condition.

Lol.. ummm, not!

That "18' x 18' room" doesnt have windows, or a ceiling, or a slab, or electrical outlets, nor does it have any additional penetrations that would cause loss of conditioned air - much of your hvac losses are due to air leaks - adding 12" to a wall isnt going to cause more leaks.