replace furnace & A/C units

Larry53September 11, 2012

I have had two quotes on replacing my furnace & central A/C unit. My home has one floor & 1100 sq ft. One company will install a gas Trane furnace w/90% upflow & 3.5 ton 80,000btus and a 1.5 ton 13 seer trane AC. They want to wrap my vent that's exposed to cold but don't think I need a new small chimney line vent for the gas hot water heater. the other company doesn't think I need to wrap the exposed vent but says I need a new chimney vent line. They will install a 93% lennox high efficiency 70,000btu gas furnace and 15.5 seer Lennox AC. Both are about $6500 total. Do i really need to wrap the exposed vent and a new liner in the chimney? Is lennox that much better than Trane? What difference do the # of BTU's make?Help!

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Both Trane and Lennox offer low end units that you don't want. Both Trane and Lennox offer mid-level and high-end units.

For each mfg, you need to provide the model numbers for these items:

1. Gas Furnace Model Number
2. Condenser Model Number
3. Evaporator Coil Model Number

The vent line (not the wrap) for the water heater is a safety and code item.

Also, it's hard to determine your cooling and heating needs on your 1100 sqft home. It depends on where you are located, what insulation you have in the attic and/or walls, and more.

    Bookmark   September 12, 2012 at 2:43AM
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I'm in southern PA. The attic has about 3-4" insulation. Don't know about the walls. Cape Cod House built in 1960.Have good new windows. The Lennox furnace is ML193UH07036B AND THE LENNOX AC IS 13ACX030. THEY QUOTED ME A TWO STAGE 96% EFFEC.(EL296UH070XV36B) & A 15.5 SEER AC (14ACX030)FOR $8400.The other company's Trane furnace was TUC1B080A9421A AND AC WAS 4TXCA018BC3HCA with a 4TTB3018A1000A CONDENSER R410A. I assume you're saying wrapping the 15' ductwork that's exposed to the cold under the house will not help that much? It's a hard crawl space to get to. They want $600 to wrap it. Do you have a better suggestion for the furnace or AC?

    Bookmark   September 12, 2012 at 7:07AM
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Just with info provided, I would say the furnace quoted Is oversized.
Where will new furnace be located?

What dies this mean to you?

Short cycling, unnecessary wear and tear, comfort issues, and higher operating costs.

What kind of exposed vent are you talking about? No one on this forum can offer an informed opinion about the need for new chimney liner. More info needed here.

What size and eff furnace are you replacing? Same with size of condenser?

Post back.


    Bookmark   September 12, 2012 at 7:52AM
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I'm replacing a 75,000btu 1983 Furnace model #394GAD02475 made by BDP CO. of carrier. It's located in the basement.
The original cape cod had about 800 sq ft and had a 300 sq ft addition built about 30 years ago on the back. The basement is under the original house. There's about an 18" crawl space under the addition. The duct work there is not insulated. In winter it does not heat the back rooms well. I could not find the label on my AC unit. The whole thing is very rusty. One estimator told me it was also 29 years old and a liilte one 1 ton unit. If I ask for a smaller unti, is that what you call a low level unit?

    Bookmark   September 12, 2012 at 9:25PM
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How cold does the crawl space get in the winter? Is it flexible duct or rigid? It may not be necessary to wrap it.

    Bookmark   September 13, 2012 at 1:19PM
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Our winter can get as loow as 0-10 degrees F. It's aluminum solid duct. When you said they "oversized" the furnace estimates, are you referring to the BTU's or condenser or both.

    Bookmark   September 13, 2012 at 4:37PM
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Your furnace's BTUs appear too high for your house. However, you need to perform a load calculation to know for sure. The load calculation takes into account your sqft, climate, insulation in walls and attic, volume of your house, windows/doors on east/west/south/north walls, etc.

The load calculation spits out your heating BTUs and your cooling BTUs based on your inputs. It's complicated to do it yourself, but there's a free online calculator at

In terms of wrapping the duct in the crawl space, you need to find out why your rooms are not getting hot air in the winter when you turn on heater.

If the main problem is the uninsulated duct, then get it wrapped. However, the primary problem might be elsewhere like leaky ducts, poor air flow to the back rooms, etc.

I misread your question about the chimney vent line. I thought you didn't have one.

    Bookmark   September 14, 2012 at 12:31AM
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WOW! I went to the load calculation site and calculated with rough figures that the total BTUs for cooling is 15,772 and heating 22,591. The sensible load was 13,971 and latent load 1801. I don't fully understand what this means but am wondering how I ask for a higher level unit that puts out much lower BTUs. I have greatly appreciated your help. Now what do I do with these companies?

    Bookmark   September 14, 2012 at 8:49AM
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The load calculator is sensitive to the inputs your provide. If you enter something inaccurate, it can swing your numbers one way or the other. So, get the inputs as accurate as you can. In particular, you might be overstating your actual insulation ratings.

I shared my local calculations with dealers that came to my house. I told them that my own Manual J calculations called for a 32K BTUs of heating, so why are they recommending 80K BTUs at 80% AFUE = ~64K BTUs.

Two of them decided to do their own load calculations and came back with smaller equipment including 60K BTU furnaces to match my 3-ton a/c system.

So, ask your dealers why they are recommending such a big furnace. It's maybe because you told them that your back rooms weren't getting enough heat, so they automatically increased the furnace size. Maybe the solution was to seal/insulate the ducts or re-balance the air flow.

    Bookmark   September 14, 2012 at 7:03PM
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