Help Needed for Furnace/AC Purchase

acaf304July 5, 2010

I live in Raleigh/Durham area North Carolina and this is my first house (built early 1950Âs, brick, one floor with walk up unfinished attic and a basement c. 1,300 sq ft., 8 supplies). I am trying to buy my first replacement ac/furnace. Both are old and the 1970Âs installed ac unfortunately has not made it another summer. The old ac is 3 ton and the furnace I am told was oversized (120,000 btu) and appropriate for a much larger house. I have no complaints about heating/cooling comfort of old system.

I would greatly appreciate any feedback on the following proposals I received from reputable companies particularly about good pairing of ac/furnace/coil, model reliability, cost and any suggestions about better alternatives to look at. I probably will not be able to use the tax credit on my 2010 tax return. Top of the line system is cost prohibitive for me but I still want a reasonably decent system.

All include installation/piping/direct venting replacing chimney output, using current duct work.

Option #1 Lennox (I preferred this contractor)

Cost: $5,472

Eligible for $1,500 tax credit

Air Conditioner 3 ton - 14 SEER - 12.70 EER - Lennox Elite series AC XC14-036

Cool Cap: 33,400 Btu

Upflow Evaporator Coil  CX34-38B

Gas Furnace - 2-stage - G61MP-36B-071 - 95.0% efficiency

Heat CAP: 43,000 / 62,000 Btu

5-1-1 programmable thermostat - Honeywell 6000

Labor: 1 year

10 years: compressor

10 years: heating parts

5 years: indoor coil

10 years: outdoor coil

10 years: cooling parts

Limited lifetime: heat exchanger

Option #2 Carrier (only given model #Âs )

Cost: $6,234.00

Mail in Rebate: $75

Air Conditioner 3 ton SEER 15 Â 24ABC636 (I think this is a base series which worries me)

Gas Furnace  2 variable speed - 58MEC100-16 - 92.3% efficiency

Unspecified thermostat

Option #3 Carrier- (Same furnace as #1 but higher SEER AC)

Cost: $7,234.00

Mail in Rebate: $$250

Eligible for $1,500 tax credit

Air Conditioner 3 ton SEER 16 Â 24APA536

Gas Furnace  2 variable speed - 58MEC100-16 - 92.3% efficiency

Unspecified thermostat

For both Option #1 and Option #2:

Labor: 1 year

10 years: compressor

10 years: parts

10 years: indoor coil

Limited lifetime: heat exchanger

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Quote number 1 seems to be a pretty decent price. I would definetly consider it.

You should ask if they can upgrade from A/C to a heatpump. It really shouldn't cost much more money. If you did that you would have dual-fuel. It would probably save you money over the long-haul. It would give you flexibility incase gas spikes again. Your climate could probably be served pretty well by just a heatpump alone.

FYI: Your probably a little oversized with 3-ton and only 1300 sq. feet. 2.5 tons should be plenty for your size place.

    Bookmark   July 7, 2010 at 7:56AM
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I would want to see in writing a properly performed load calc.

and I would want a good two stg thermostat for that two stg furnace-definitely not what Lennox dealer quoted. probably HW 8321 would be fine.

while I do like HPs for your area/climate, I would not recommend one for a home your age unless it had good insulation properties.


    Bookmark   July 7, 2010 at 8:05AM
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Thank you so much for your responses!
I am also concerned about the 3 ton size. Two contractors recommended 3 tons and 2 recommended 3. I thought maybe Lennox did not make this model in the 2.5 ton size. The Lennox contractor said he would come back and do a load calculation.
Thank you for the better thermostat suggestion. Are you satisfied with coil choice? I thought I would also see how much more the 2 stage with variable speed motor would cost and would consider especially if you thought this would be an advisable upgrade. I also wonder if the furnace is on the large side like the ac.
I only use gas for heating and have been paying c. $700 for the heating season. I donÂt think my home has good insulation properties so the heat pump may not be best option. I may add more to minimum insulation that is in the attic but have no plans to replace old windows.
Again thank you for your feedback.

    Bookmark   July 8, 2010 at 12:46AM
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Have an energy audit done first and follow up on its recommendations. You will likely need to upgrade some insulation and seal some air leaks.

Have a Manual J done after the upgrades. You should be able to get by with a much smaller system that will cost significantly less to operate than what you are paying now.

Some of this can be done using tax credits. An up front investment in improving the house's thermal envelope will pay real dividends in the long run.

    Bookmark   July 8, 2010 at 7:23AM
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I received the following load calculation results from the Lennox contractor(Option #1 in my first posting). He said he would get me a copy of his report.

Cooling Load @ Outdoor Temp 95 Indoor Temp 75 Zone 1: 28,646 btuh
Heating Load @ Outdoor Temp.10 Indoor Temp 70 Zone 1 37,339 btuh

He is sticking with his original recommendation for $5,472.00:
Lennox G61MP-36B-071 2- stage furnace
XC14-036 air conditioner
CX34-38B upflow evaporator coil
Honeywell 6000 thermostat (note 2-stage furnace without variable speed)

Does this load calculation match up with his ac/furnace choices?
To me 2.5 ton ac seems better fit for c. 1,300 sq feet. home even without good insulation. Not sure about furnace size.
He insists thermostat works well with this configuration.
Does this additional information put me anywhere near the right track?
Your advice is very much appreciated!

    Bookmark   July 13, 2010 at 11:18PM
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My only issue on your load calcs is how do you estimate air infiltration on a 1950s house. Did he do a blower door test - not likely. I mean this number is anybody's guess. Then - do you have leaky ducts - most likely yes. How much?

Did your 3 ton work well - ie did it cool enough on hot days?

If your old 3 ton cooled the house well and even shut off in the afternoon often, then I might go to 2.5 tons. I think this would be a better indicator than a load calc with all the air infiltration/duct leakage variables.

FYI - $700 heating bill here (this winter) for 4000 sq feet. Buy $$ standards, you might need more heating than that load calc would call for. I have 7 tons (sized for expansion, 10+ ft ceilings, and lots of windows).

    Bookmark   July 14, 2010 at 5:34AM
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    Bookmark   April 15, 2011 at 3:16PM
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