HVAC replacement, options for upstairs

pdb5627June 15, 2011

A routine HVAC checkup indicated that our AC compressor and fan are at their end of life based on Megger tests, so now I am thinking about our alternatives in replacing the AC system. I expect to be talking to a number of contractors to see what they propose, and I would like to get ideas for what can be done in addition to replacing the air conditioning.

One issue in particular that I would like to address is that the upstairs of my two-story home tends to be significantly warmer in the summer and cooler in the winter than the downstairs. In summer, we then have to mentally account for the temperature difference when we set the thermostat (downstairs) for nighttime so it will cool off the upstairs enough for us to sleep comfortably. I think that one of the more significant things we can do to make our house more comfortable to live in is to get better regulation of the temperature upstairs.

I don't know a whole lot about heating and air conditioning, but my ideas would be to consider improving the attic insulation somehow and/or to somehow have the upstairs and downstairs temperatures able to be regulated separately. The technician who was out to check the air conditioner mentioned a variable-speed blower as a possible help, but its not obvious to me how that would help.

Also, at some point in the future, we would like to finish the unfinished basement. Does that make any difference to selecting an air conditioning unit now?

Any ideas or advice? My feeling is that contractors will be focused on selling and installing a new central system, not looking at other aspects of the system or the house as a whole.

Possibly useful background information


Location: Omaha, Nebraska

House: Two story, approx. 2100 sq. ft not counting 1000 sq. ft. unfinished basement

Age: Constructed ~1996, still has original HVAC system

Heating: Natural gas furnace

Attic ridge vent was added to roof last year and has seemed to help the summer temps upstairs somewhat

Attic insulation is 12 - 14 inches of blown in fiberglass

HVAC vents are in the floor downstairs and through the ceiling upstairs with return registers near the floor on both levels

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several questions.

your upstairs ductwork is run through a chase and supply lines are from the ceiling?

furnace is located in basement?

what size and eff is your furnace?

what size is your AC condenser?

what is your electric rate?

usually the upstairs temperature difference indicates poor ductwork design/ sizing rather than size of your AC.

post back.


    Bookmark   June 15, 2011 at 4:12PM
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Your upstairs ductwork is run through a chase and supply lines are from the ceiling? *YES*

Furnace is located in basement? *YES*

What size and eff is your furnace? * 101,000 BTU/hr output, 80% efficient*

What size is your AC condenser? *Not sure on nominal rating. How could I tell?*

what is your electric rate? *$0.09 to $0.11 per kWh depending on if you roll the service charge in or not*

    Bookmark   June 15, 2011 at 4:29PM
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get the mdl number of the AC condenser off the data plate which should be on one of the sides of the outside condenser.
another question-cost/therm for nat gas including all charges.

do you know if you have supply damper on the main supply trunk lines to downstairs and upstairs?

post back.


    Bookmark   June 15, 2011 at 5:00PM
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AC condenser is badged as a Carrier Cobra, Model # AA1CJ048-A.

I do not believe that I have any supply dampers on the main trunk links to upstairs and downstairs. A neighbor has previously mentioned that he does have them, and we looked but did not see them at my house. If they are here, we weren't able to find them.

    Bookmark   June 15, 2011 at 5:42PM
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Does the additional information help anyone offer any suggestions? Even advice on what questions to be asking contractors to get them looking and thinking in the right direction would be helpful.

    Bookmark   June 21, 2011 at 9:01AM
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at the very least I would add damper control for supply air between first floor, second floor and basement.

I would look at an 80K 95+% eff furnace that would include the new full modulating furnaces like York/Luxaire and Carrier/Bryant Infinity systems.

It appears you have a four ton AC condenser which on the surface sounds oversized. I would discuss with quoting dealers.

Any hot/cold spots in your home should be pointed out to dealer for possible improvement.

Do you have adequate return in your home's ductwork?

Do you have a pleated media cabinet? if not, I would add one.


    Bookmark   June 21, 2011 at 10:02AM
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