Central A/C Proposal - Seem undersized?

stuntmanmikeJanuary 29, 2012

Hi HVAC experts.

I recently got a quote for a new a/c install, 1750 sq ft house with radiators, so would involve running new ducts and such. A 2 Ton Airease 13 SEER system was quoted. Think that's enough horsepower? House is circa 1840 and has relatively low ceilings, but single pane glass with some insulation.

Please let me know if this seems woefully underpowered or if you think it could work. It was also suggested that we only put in one zone, with the thermostat on the 2nd floor.

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tigerdunes

Mike

What is your location?

What is your fuel for the radiators-nat gas, oil, propane?

What eff is your boiler?

Yes, I would say a two ton is probably undersized by up to one ton? You will only know for certain by getting a man J load calc for correct sizing. Keep in mind ductwork has to be sized correctly as well including adequate return for best airflow and overall comfort.

New ductwork should be insulated min R8.

I might even consider a HP depending on your location to handle heating needs for above freezing temps. Of course, I would want to know your electric rate and the cost of fuel for your boiler and its efficiency.

IMO

    Bookmark   January 30, 2012 at 7:30AM
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mike_home

Can you provide some more details? Are you keeping the existing heating system and adding central AC only? How and where are the new ducts and returns being installed? Why only one zone if the house has two floors? Where will the air handler be installed?

It is difficult the tell if the size is too small. It would seem it would be undersized based on the house probably does not have much insulation. You need to have the contractor explain the reasoning behind his recommendations.

    Bookmark   January 30, 2012 at 10:19AM
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stuntmanmike

Hey guys, the house is in the hudson valley, ny. Keeping the hot water system but good call on adding heat pump for above freezing days.
Installer came back and recalculated, suggesting a 2.5 ton system (3 ton air handler.).
Airease equipment ok? Seems like a builders grade lennox and that it may share coil and internals with other premium brands?

Thanks

    Bookmark   February 7, 2012 at 8:30AM
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tigerdunes

Airease is mediocre HVAC.

I would want to see the load calculation in writing. Not convinced that 2 1/2 ton might also be undersized for an old home with questionable insulation and building envelope properties.

Where will ductwork be placed? Crawlspace or attic? Ductwork insulation should be minimum R8 if not higher.

What is your fuel for the boiler and it's cost? What is boiler efficiency?

IMO

    Bookmark   February 7, 2012 at 9:46AM
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stuntmanmike

Hi guys, oil fired boiler is circa 2007, not sure of it's exact efficiency.
Ductwork to be run from air handler in attic and will be insulated.

    Bookmark   February 8, 2012 at 3:39PM
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tigerdunes

stuntmanmike

Since your fuel is oil, your boiler is probably around 80-85% efficient.

What is your electric rate?

I would look into installing a good quality HP instead of straight AC. HP should have electronic demand defrost. I would not have an Airease.

IMO

    Bookmark   February 8, 2012 at 3:56PM
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neohioheatpump

I agree with Tiger completely, if your heating with oil, and planning on getting central a/c, spend a little more and updagrade to a heatpump. I'm assuming you don't have crazy expensive electric ofcourse.

I would probably go with 3 tons. That might be sized better since that house is so old and the sq. footage. Where are the vents being retro-fitted into? Basement or attic?

    Bookmark   February 9, 2012 at 12:38PM
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