Quote:
Originally Posted by RVJim
Slightly undersized is better than oversized. Far better to have longer run times versus short cycling. You might consider a variable heat pump if you replace it. I have a Carrier variable speed heat pump that is slightly undersized by performs well year round. As pointed out, get the calcs from the building department and see what they recommend. The size of the unit is just one variable in cooling a home - there are others including supply duct sizing, return sizing, type of inside unit, window sizing and direction etc etc.
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Well said. I built a house in Pennsylvania and put R-60 insulation in the attic—much more than what houses have here. I told the HVAC company what I was doing and that the AC size should be decreased accordingly, but instead they put in their usual size. The predictable result: the AC would run a few minutes, quickly cool the house, then turn off, but it didn’t run long enough to extract much humidity, so the house felt humid. Turning down the thermostat so the AC would run longer just made the house cold and clammy. I had a little gadget installed that fooled the heat pump into running less powerfully but for much longer, and that solved the problem. But it cost $1,000 installed. Running longer with a smaller but more efficient heat pump is much more cost efficient for you and yields better cooling with less humidity. Chances are, your smaller unit is the right one for your house. My home here in The Villages is 24 years old and has much less insulation than I’d like, tramped down by workmen over the years, but from April to November I keep the AC on at all times, set at 74°, and never leave doors open. My electric bills are remarkably low, I think. While I could have more insulation blown in, I think it would take a number of years to recover the cost.