Posted By engineer on 02/18/2008 7:04 AM
Beware sizing for heat load.
Oversizing the unit so as to avoid operation of strip heat on coldest days has two downsides:
1) AC will cycle off too quickly before properly dehumidifying the house. I realize Iowas has a cold winter but comfort during high humidity days is an important factor.
2) First cost of larger unit - both the unit and much of its ductwork would be bigger and more expensive, possibly also noisier.
Consider ways to better insulate or tighten envelope to reduce heating load.
I concur with advice to spring for a 2 speed unit.
All the units we priced are three stage heating and two stage cooling. Our biggest worry is that with a 3 ton unit we would spend the majority of the winter in the third stage of heat. We understand that on the very cold days that the third stage runs. The insulation will be R49 attic and R19 side walls (cellulose) with a geo caulking package. The basement will have an R10 blanket on the walls. One heating contractor told us that for the cooling side they slow the first stage fan speed down. This makes the fan run longer and dehumidifies the house. The price between the 3 and 4 ton unit is approximately $1200. Thanks for the insight and opinions. |