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Heating & Air Conditioning

AC and Attic Furnace Replacement Issues

8 years ago

I moved a few years ago to a 5,000 s.f. house in central Ohio that was built in 1989. It has a year 2000 Rheem 4-ton AC for my 2nd story that just died. (The upstairs is probably about 3,000 s.f.) Repairing this R-22-based unit is prohibitively expensive (multiple coil leaks). So, we are getting quotes for a new AC and will probably go ahead and replace the attic furnace(s) at the same time. The furnaces are also about the year 2000, also Rheem, and are set up as twinned 70,000 BTU units.

We have gotten three quotes for replacements. None of the dealers like this twin setup, but the attic opening--limited by the 24" spread between trusses--is too small to get the recommended 110,00 (or so) BTU 2-stage, variable-speed blower furnace we would like to get. All of them agree that we can get only 80% efficiency due to condensation issues in the attic with high-efficiency furnaces. The Rheem and Lennox dealers said that twinned units can't have variable-speed blowers. But the Trane dealer quoted me for two (twinned) TUD2B080 60,000 BTU furnaces, which do have the variable speed blowers. He said it would be fine.

So, I am not sure what to think. I would really like to get variable-speed if I could but don't know if will cause all the conflicts between the two blowers that the Lennox and Rheem dealers mentioned.

Thanks in advance for any thoughts and advice.

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Comments (4)

mike_home
8 years ago
The first order of business is to find a contractor that will do a proper load calculation. The contractors you have talked to so far are guessing at the size, or sizing based on area which almost always leads to over sized equipment.

A condensing furnace (90%+) efficiency can be installed in an attic provided you know how to do it. It requires wrapping electric heat tape on the condensate line. This will keep the condensate from freezing. See if you can find a contractor who will do this for you.

There are several Carrier furnaces which are 21 inches wide. You would need to check the depth. I would think a 80K BTU furnace at 95% efficiency would keep the second floor toasty.

I would rather see you spend money removing the attic pull down stair rather spending the money on twin furnaces. Getting an 80% efficiency furnace would not be terrible, but the last two winters in Ohio have been brutal. The extra money for a higher efficiency furnace is going to pay for itself in few years.
Andrew Cameron thanked mike_home
Andrew Cameron
Original Author
8 years ago
Thank you for the very helpful comments. I am not sure why no one has suggested a load calculation. That makes a lot of sense. I will ask about that.

It's also great to hear that it might be an option to go with a higher efficiency furnace. I would rather go that route and would have no problem removing the pull-down stairs and making some other adjustments to fit one through the opening.

I will check with a Carrier dealer on the 21-inch wide furnaces. That is good to know as well.

Again, I appreciate the great suggestions.
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For $4000 he thinks you "might" have a solution? Wow. Did the guy do a heat/loss analysis? He wants to give you the same size furnace. What is the continuous flow option? Is that a variable speed blower? I think a VS blower run all the time will help to even out temps, but what i cannot get is that an 80k system is having a hard time heating 1200ft of space. My whole house is heated with a 100k system and its 1800ft. I never have more than a 3 degree temp diff btw floors if at all. I did however focus on insulation and draft blocking (real cheap to do) to get that. Heat wise is there something special about that bedroom that it wont heat? Ductwork issues: loose boot at register or going thru uninsulated walls? What does the room look like. Are there dropped ceilings is it under an attic space etc. Are the walls insulated or does it have a million windows. So many questions and probably cheaper to find solutions to your problem than dishing out 4k.
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mike_home
8 years ago
Here is a link for the Carrier 59TN6 furnace.

Take a look at page 13. The width for the 80K BTU is actually 17.5 inches with a length of 29.5 inches. The 100K BTU has an 21 inch width. I highly doubt you need that size. The sizes of other furnaces will be either one of these two widths. The widths are consistent so they will match up with the width of the that sits on top or below the furnace.

The 80K BTU furnace weighs about 67 pounds. It should not be that difficult to lift it up through the attic opening even without the pull down stairs.

Have the duct work in the attic inspected for any leaks. If you have flexible ducting, and it looks like a mess to your eye, then it should be fixed before installing a new furnace.
Andrew Cameron thanked mike_home
Andrew Cameron
Original Author
8 years ago
That's a tremendous help. Thanks again. I was just looking through the Carrier website to find the furnace dimensions. You pointed me right to a great unit. It has all the features I was hoping to get. And if the 80K BTU one would be sufficient, that would be fantastic. I did call a Carrier dealer who will come tomorrow afternoon.

There is flexible ducting in the attic. I will have them inspect that and will be sure to get it fixed, too, as you suggested. At the very least, I know some of it has lost the wrap around the insulation.

I really appreciate all the expert advice.

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