What size unit for a home

My parents want to upgrade the Heatpump and indoor unit, they claim that it runs constantly on hot days, it is a 23 year old house and the insulation isnt the greatest, I dont want to replace it with a reccomended size for the insulation issue, how much bigger of a unit may I step up to befoe short cycling occurs, I have also heard of swaping reccomended size units between indoor unit and out door unit The house is a bi level house approximately 2800 square feet 1500 up stairs and 700 down stairs with a single garage below the master bedroom (square footage listed did take out the garage space)

your asking for someone to guess it doesn't work that way you need to have a pro. do a heat load calc on the house to determine the correct size unit

What part of the world do you live in ?state.how tall are ceilings ,how many windows ,to many variables to do over comp. But if this helps in TX we go off 400-450 sq ft per ton for those 115 degree days

[Edited by e_giles on 08-26-2004 at 09:24 PM]

"the insulation isnt the greatest"

First and cheapest place to start. Then caulking and weatherstripping.

A properly sized unit DOES run all the time on a very hot day. What does it do the rest of the time?

Yes, running a lot is proper for AC/heat pump. You can do your own heat loss/gain calculation with HVAC-Calc

Your question is just a little like asking "how big an engine does my truck need?". Like several others I would pony up $50 and get a copy of HVAC-CALC, and use it to do a load calculation. That's what I have done for my house and it gives me a certain amount of confidence what is the right size heating or AC unit.

The program is easy to use, as promised. There is a whole thread about HVAC-CALC with generally high praise. There are other programs out there but I don't know of one as easy to use at this price.

One thing I have learned, is inadequate AC performance by no means tells you the unit is "undersized". Most of the time it tells you there is a duct problem or other craftsmanship issue. Makes the problem thornier but different, maybe cheaper but definitely more work to solve.

Once again, I cannot emphasize enough how important it is to get a load calculation done. If you really don't want a do-it-yourself program, then get a few HVAC companies to do a load calc as part of their bid, before you buy anything else. And keep your "baloney detector" working <g>!!!