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Heating & Air Conditioning

Central A/C Proposal - Seem undersized?

12 years ago

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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Comments (7)

tigerdunes
12 years ago
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
mike_home
12 years ago
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.
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The system is probably not undersized. More likely, you have an inefficient system and leaking ductwork. Do you have a lot of dust? Do you have mold growing around refrigerator door and in the bathroom? If so, ductwork needs to be replaced. New ductwork needs to be sealed properly! Also, location of air handler is a problem. When the ac runs, does the AH sweat? If so, this indicates a further (large) loss of efficiency. Moving AH to basement and installing properly sealed ductwork will easily save you 15% or more of your energy dollar. Best and cheapest (by far) way to save money is to re-insulate your house. Brand? Get the right contractor. Then, look for Trane (American Standard) and Ruud (Rheem). Other brands are not far behind. No matter what brand, get the right contractor. You can investigate brands until you are blue in the face and still end up with a terrible system.
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Comments (11)
Ryan I agree. A 3 ton unit for 1700 sq. feet should be fine unless you have very poor insulation. I have two independent zones. My upper floor is 1650 sq. feet. The load calculation came out to 2.47 tons. I am cooling it with a 3 ton Carrier Infinity 17. I used to have a 2 ton unit which struggled on very hot days. My lower floor is 1550 sq. feet. The load calculation came out to 1.43 tons and it is being cooled by a 2 ton Infinity 17. If you are interested in getting an additional quote from a Carrier dealer, then below is the contractor I used. He did a very good installation for me and his prices were very competitive. He will do Manual J calculation and do the forms for the NJ WarmAdvantage and CoolAdvantage rebates. The Ice-Man 4 Featherbed Lane Hopewell New Jersey 08525 (609) 921-1151 (609) 771-1119 (609) 466-9020 You need to hurry in order to qualify for the Carrier rebate. You need to buy by June 30, and be installed by July 15. Good luck and let us know the final outcome.
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The price of propane is rising, isn't it? In this case, I'd consider heat pumps that will switch over to propane when the temperature is low enough to warrant the use of propane over the efficient heat pumps (around 35-40* or so). Few matchups will get near the 19-20 SEER range. You need the sizes and full model numbers of the equipment being quoted to know for sure. Trane, Carrier and Bryant all make fine products. If going with Carrier, ask for a tin-plated copper coil (heard of leaking problems with Carrier's *ACA standard copper coils--I guess all mfg's have leak problems). The Infinity/Evolution is a nice system. I personally favor Trane over Carrier--I think Trane's quality is hard to beat, but that's just my opinion. I do wish the XL19i was available in R410A, but that will be a little later. Is your electricity particularly expensive? Going with the top-of-the-line SEER/units may not have a great payback. 20 years old? They've done their time. As far as duct noise goes, if your ductwork is sized correctly, then you should be fine. However, the variable-speed blowers maintain proper CFM and will overcome slightly deficient ductwork systems. If the ductwork system is undersized/deficient, it will be louder as it attempts to maintain proper CFM (versus the PSC blowers where if the ductwork was poor it wouldn't vary its speed to maintain airflow). If it's quiet now, I don't think it will be a problem--I'm just pointing this out about variable-speed blowers. Once you get a few quotes, post back with the info and we can advise.
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It seems strange that you have independent heating and cooling duct work. Is this an old house? Maybe the AC was installed after the house was built or underwent a major renovation? The heating duct work could be used if it is large enough to handle the air flow. The furnace becomes the air handler. If the furnace is old then it may make sense to buy a new furnace when the coil is installed. I think installing air handlers and duct work in uninsulated attics is should be avoided whenever possible. So moving everything to the basement would be a good idea. If you want to keep the air handler in the attic then enlarging the access to the attic should be easier and cheaper than opening up the roof and hiring a crane.
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stuntmanmike
Original Author
12 years ago
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
tigerdunes
12 years ago
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
stuntmanmike
Original Author
12 years ago
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.
tigerdunes
12 years ago
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
neohioheatpump
12 years ago
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?

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