First Time HVAC Purchase - Please Help Us

dad4diyNovember 6, 2013

We are replacing a 25-year-old Carrier 100K BTU furnace and a 4-Ton AC unit in a 2-story 2,900 sq. ft. home in Wisconsin. Overall, the heating and cooling has been okay for the 3 years we have lived here. The worst problem is in the summer when the second floor runs about 5 degrees warmer than the first floor. We have narrowed it down to 2 dealers:

Carrier: 59MN7100 97% furnace and 24ANB748 17 SEER AC unit with a Infinity Touch thermostat and 4" pleated media filter. $7,900 after rebates

Rheem: RGFG-10EZCMS 95% furnace and 13AJN48A01 13 SEER AC unit with Rheem Communicating Thermostat and 4" media filter. $7,800 after rebates

These prices are without any zoning. I am getting mixed messages about the need to split the two floors into zones. One company tells me that the new motor will run all the time and circulate the air better, eliminating the need to spend 3K more on zoning. If needed I will add zoning later as a second trunk line will need to be added. Any thoughts on this?

Also, are whole house humidifiers a good idea? One company mentioned adding one for $450.

Any advice on the brands or the setup is much appreciated. We would like to hire someone this week. Thanks!

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The Carrier quote is the better equipment especially with the nicer AC condenser. Good pricing. I assume this includes all manufacturer rebates plus any state and federal tax credits.

What model evap coil quoted? Be specific.

I would want the Carrier dealer to make specific recommendations to improve temp consistency between the floors short of zoning control. Is there adequate return on both floors?

Whole house humidifiers can improve your comfort and help maintain home's humidity range if that has been a problem in the past.


    Bookmark   November 6, 2013 at 6:50AM
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You can be the judge of whether a humidifier is needed based on your experience in the house. Low winter, heating season, humidity is largely due to air leakage from the house. If you have a well-sealed home, your needs for added humidification will be low or none.

    Bookmark   November 6, 2013 at 2:44PM
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100K for a furnace is oversized. Your old unit was giving 75K output, a New 80K @ 95% will give you the same 75k output.

I'd look at a separate system for upstairs and a smaller system just for downstairs.

    Bookmark   November 6, 2013 at 10:34PM
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I agree on the furnace is being over sized. If the old 100K BTU worked well on the coldest days, then a 95% 80K would be the right size. It would be better if you had a load calculation to verify all sizes.

If you did not have humidity problems in the past, then don't spend money on a humidifier.

My vote is for the Carrier equipment. The variable speed furnace may help your second floor problems, but it is not a substitute for zoning.

    Bookmark   November 7, 2013 at 9:22AM
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In Wisconsin you will run the system often enough to dry the air significantly in the winter, so a humidifier should increase your comfort. The humidifier will include a humidistat, so it will sense the moisture level in the air and should only run when you need it.

However, my experience with whole-house humidifiers is that cheap models are not the most well-designed or trouble-free device in your HVAC. They have water pumps, water filters, water lines, and other parts that fail or need significantly more frequent maintenance once they are a few years old. They are also piped into the plumbing system, so there is always the possibility of a leak causing a significant mess.


    Bookmark   November 8, 2013 at 6:11AM
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How much a heat is needed has direct bearing on how much humidity needs to be added to the inside air. What causes "dry air" inside are high inside/outside temperature differential, low outdoor humidity levels, and lots of air exchange from the house to outdoors.

Of course, if your heating plant sucks lots of outside air in from outdoors due to the need for combustion air, and due to pressure differentials caused by poor ducts, running it a lot will indirectly cause loss of moisture generated by normal living activities.

If the house is tight, the need for a humidifier is reduced or eliminated.

    Bookmark   November 8, 2013 at 9:54AM
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While the issue of the sizing of the furnace is not inconsequential but certainly not as big a deal since the Carrier model quoted is a modulating furnace that operates between 40 and 100% of output. If your current furnace is a 100 KBTU model at 80% efficiency, then I probably would lean toward the 80 KBTU size.

And yes, ask your Carrier dealer to make some specific recommendations to improve floor to floor temp consistency.


    Bookmark   November 8, 2013 at 10:45AM
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