wildly different HVAC proposals

tom_49

As others have said, you HAVE to go by the heatloss calc. done on the house. Do not install equipment that is too big " just to make sure its enough". You will be living in a very uncomfortable house for a long time. And wasting energy ( and $$$ )for no reason,none.


Judging by the size of the house and the 2x6 const. my best guestimate is 4-5 tons MAX. Again, Im just guessing, but I have been at it for 20 yrs.

One thing I would recommend is 2 speed equipment. I was in a house yesterday that we put a furnace in(60,000 btu for 2000+ sq.ft.replacing 100,000 btus)and a/c ( 3tons,2speed). It was a Carrier Infinity system. The thermostat keeps track of hi and lo run hours. The furnace ran at lo speed, 2/3 of the time, that is 39,000 btus heating a 2000+ sq. ft. house in Mass. The a/c ran on low speed 3/4 of the time , Thats 18,000 btu ,1 1/2 tons. My customer was thrilled w/ his energy bills and comfort.

Good luck, tom

[Deleted User]

wildly different HVAC proposals

Hi all. I’ve got a question regarding HVAC for a new construction house that I’m building myself, and I’m not too sure that there is an easy answer. So far, I’ve gotten two proposals; one from a large, well known company and another from a small, family owned company. Both are for two zones; one being a heat pump w/ gas backup on the first floor and finished, walk-out basement (approx. 2700 sq. Ft. total) and the other being a separate heat pump for the second floor loft, bath and bedrooms (about 700 sq. Ft.). But, the capacities vary wildly. One proposes 3.5 and 4 ton units and 130K BTU while the other only 2-ton units and 60K BTU. The house is 2x6 construction, but they both know that and both did a walk through. I don’t want to get a system that is undersized, but then again, I don’t want something that is too powerful either. Is there a way that I can check to see whose numbers are more in line? FYI, I’m in Maryland, if that makes a difference.
Thanks in advance for your input.

Eric_25

the neighbors house too

You need to get a computerized load calculation done, the four tons seems more in the ballpark for 2700 Sq.Ft., with 7.5 tons you should be able to cool the neighbors house as well as your own. We use yhe Wrightsoft load calc. software and it works great, someone in your area must use it also.

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Ragu_5

Mike...

Did you try the "Find A Professional" section of this site? There may be somebody who advertises here who also services your area. Very much worth a shot. Good luck.

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Dale

size

I'll start by saying that I personally know of only one house that has a correctly sized furnace, meaning at design temp. - 10 here, the furnace never shuts off and the house stays at 68 degrees. All others are oversized, including my own 60K 1970"s 1500 sq' house. The key as the other post suggested is the heat loss and heat gain for your area. Also, you need to provide the construction details in detail to know the numbers. What kind of windows are you putting in? How many sq ft of glass, are you wrapping in tyvec? This determines your infiltration rate. Keep in mind that the results from the software are conservative. For instance, there are 3K sq. houses where I live in Wisconsin that have a heat loss of 24,000 btu and a heat gain of 9000 or so. These homes have a 40,000 variable input furnace and a 18,000 btu ac because that's what's available. I haven't looked at I'm guessing air to air heat pumps in awhile so the the heating input per cooling ton will need to be checked. Size as small as possible, the equipment lasts longer the less it cycles. It's humid where you live so the AC should really be 10% less than design figured to max dehumidification.

S Ebels

The crux of the question is

What is the correct size for your house. This can be determined ONLY by your contractor doing a heat loss/gain calculation on your home. So then the question for you becomes, which contractor did the calc and which one didn't........maybe neither one?

I have a gut feeling that I'd HATE to live in a house that size with 7.5 tons of air blowing through it. Every time it ran you would feel and sound like you stepped into a wind tunnel. Your house would about have to be solid windows to warrant that kind of capacity. Not to mention the fact that you're going to have some seriously sized duct running around in there causing havoc with your framing. Just guessing here but a rough, very rough rule of thumb for a new house is 30 btu's per sq ft on the high side. 3400 X 30 = 102,000 btu's. Let me say again, that's a high guesstimate.
Wouldn't be surprised to see your actual load at less than 60,000 or about 5T total.

I/we/everyine here can rattle on forever with guesses but you need to get a load calculation done before anyone, most importantly you and the contractor can make an intelligent and informed decision.

Boilerpro_5

Calculations need to be done

But I would be inclined to think that two 2 ton units is too much cooling, but maryland is a bit warmer than here in northern Il. Two 60,000 btu/hr furnaces may also be bit oversized. The other proposal sounds ludricrous.

Boilerpro

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Steamhead (in transit)

What part

of Maryland are you in?

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