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It depends...

Posted by jb on August 8th, 2001 12:18 PM
In reply to Air conditioner by Suzann on August 7th, 2001 03:41 PM [Go to top of thread]

The ONLY correct answer to this question is:
"it depends"

This is a pretty large unit. If you put it in a house that really should have a 3 ton unit then your house will be cold and clammy. This is because it will get down to temp. too fast and not dehumidify. The unit needs to run for long periods to have a chance to take the moisture out of the air, which is extremely important to comfort levels. Different houses have different "heat gain" loads, i.e.: how fast they gain heat from the outside. Factors include insulation values, construction techniques, type and number of windows and their orientation, etc. etc. etc., even down to how many people will be in the space. You need to find at least 2 or 3 HVAC companies that will do a REAL heat gain (manual j) calculation to see what is best for your house. If someone tells you you need an "X" sized unit without doing the calculations (and showing you the results and report, in detail) then they are selling you a bill of goods. "Rule of thumb" guesstimating is not a good way to size a system. I had a guy from Sears tell me OVER THE PHONE that I needed AT LEAST a 4 ton unit. He based this "wild assed" guess on the fact that I had a colonial type house, sight unseen! Two reputable installers did their manual j's (or equiv.) and both told me I needed a 2 ton unit and it works great! You can get in the ballpark by doing your own calc's in an hour or two. $39 buys you a one time use of hvac-calc at or at Harold's web site (I think). Since you aren't a pro you might only be "close" probably within a 1/2 ton or so of accuracy because you don't know about shading or people loads etc..

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