What are options when there's oversized hvac?

1779 Views 5 Replies 4 Participants Last post by beenthere, Feb 21, 2013

strategery

Discussion Starter · Feb 19, 2013

I don't think my hvac installer ever did a manual j, they just switched out the same size furnace and central ac. I have roughly 800 square feet of conditioned space with an unfinished and uninsulated basement. Both the furnace and ac short cycle and I'm constantly battling with the thermostat. It's most uncomfortable during summer evenings when the temp is dropping but the humidity is still the same.

Obviously I can just find a new hvac company to do a manual j and have them install the appropriate sized furnace and ac but the units are only 4 years old and it will cost a lot of money.

Can I make some adjustments to the equipment so they run longer and at lower capacity? The furnace is a 2 stage. I don't know much about the ac except it is a 2 ton 15 seer.

For cooling, I hardly need anything because I'm completely shaded in. I live in climate zone 5 so there's a lot of humidity. Would it be wise to talk to someone about installing a whole house dehumidifier?

The house is a hundred years old but has had a lot of remodeling done and it is pretty well insulated (batts in the walls, lots of insulation in the attic, rim joists foamed).

Thanks!

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yuri

· #2 · Feb 19, 2013

Ouch, you really need a 1.5 ton unit and unfortunately there is nothing you can do to get rid of the extra 1/2 ton capacity you got. Slowing down the furnace fan will just cause it to freeze up. A whole house dehumidifier is quite expensive, uses a lot of electricity and is basically a bar fridge with a fan attached to it. It needs to work off your ductwork as a bypass unit and I doubt you can get one small enough for your house. Good for Florida etc but they are pricey specialty units. Best bet is to get the proper sized AC and maybe you can sell your existing one with Craigs list etc.

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yuri

· #4 · Feb 19, 2013 (Edited)

if you can get one and DIY then go 4 it. you need to know the specs in airflow thru it and how it works with your furnace and interlocks with it etc. not sure about heat pump sizes as I don't sell them. I believe the aprilaire unit is the same one Lennox sells as they just rebrand it for Lennox so it should be good. I just looked up the install info for the Lennox and if you absolutely have to you can just park the unit in the basement and take one vent/return from upstairs and shoot another supply one upstairs w/o having to use the furnace. if you use the furnace you need 6" between where it takes off on the reutrn duct to where it reattaches to the same duct which may or may not be possible 4 U. you should download the install manual for it B4 buying it as it is not as simple as it looks.

DIY load calc

http://www.hvaccomputer.com/gtarget1.asp?kwx=6&adx=3&gclid=CMjGvu7Kw7UCFe4-MgodPF4AoQ

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