I want to make sure I’m not being ripped off, how do you calculate this? For a house with a 1750 sq ft floor with 10′ ceilings throughout what do I need? I was recommended a 4 to 5 ton unit. How do they decide what size I need? We will be building a 2nd house later that is 2400 sq ft with 10′ cielings, what size will we need for that one?
Thanks,
Johnny
Replies
yo johnny,
i'm a builder and when i first started i listened to the subs. after getting burnt a few times i began learning everything about building i could including hvac. i always run heat loss calculations on houses and additions. i never use approximation tables. once you have these numbers you will be able to determine tonage or btu usage. for a rough approximation for a house with 2x4 walls and moderate windows, you can allow one ton of ac for 600 sq ft of living space. you must back this quess up with solid calculations. find subs who understand how you think...good luck.
Try http://www.hvac-calc.com
Wow that seems big for that size home. I think ours is a 3.5 ton for an old 1966 ranch home 1 story and basement 2200 square feet total. I was told the unit was a little big for the house but at $600 I didn't care.
jeffwoodwork,
You really should care! The bigger the unit the higher your electric bill will be.. First cost is but a tiny fraction of the real cost of a HVAC unit.. (doubt me? add up your electric bill for the past decade)
Ideally it should be sized to have to run continously under worst case conditions.. if it is cycling on those really hot days you are wasting electricity and going to need to replace it sooner..
NO! running continously doesn't overwork them! It's the start and stop that gets to them. Which is worse on your car? a thousand mile trip or running around town? Same with A/C
Exactly right! And an oversized unit won't dehumidify properly.Andy Engel
Senior editor, Fine Woodworking magazine
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None of this matters in geological time.
I said it was a little big it could have been a 3 ton unit it was borderline so the 3.5 was just a bit more than needed.
Well he did a calculation and said a 4.5 ton is what would be recomended so we figured we'd go with a 5. Remember we are building 10' walls throughout the entire house, if that makes a difference. I live in S. NM so generally speaking there is not alot of moisture in the air normally so I don't think that should be a problem.
Johnny, it will all really depend on the load calc as folks have said, but for a quick comparison, we just had central air install. Our home is a little bigger than yours, and they speced a 3 ton unit. Keeps the house very dry and cool. We went with a variable speed air handler unit, which is supposed to remove more moisture from the house. Works well.
Again, the construction of your house, location, environment all play a role.
Even if your guy did a rough calculation/estimate, he should be more specific rather than a 4 or 5 ton system.
6milessouth