Gas and Oil Home Heating Furnaces - Flipping a downdraft furnace?

I'm having overhead ductwork installed to replace my under-slab ducts, and I'm just wondering if there's any sense in seeing about converting my downdraft furnace to updraft mode (it is the convertible type, 80% efficiency rating). Would the cost to do that make it more sensible to just replace the furnace at this point? I have to replace the A-coil anyhow. Thanks for the input, guys.

We need more info.. Make and model # of the furnace?


some you can't change, and other you can.

Thanks, Jay -
The unit is an Aire-Flo AF80 (made by Lennox), which was installable horizontally, upflow, or downflow. I'm guessing it can be converted, but don't know if it would be economically worthwhile. I appreciate your help - thanks again!

-Bert

How old is it?

Honestly, being you are in the norther part of the states with cold winter, I would update it to a 90% furnace.

Well, I'm not planning on staying in this house for a whole lot longer, but it's probably wiser to just replace everything and start clean. Thanks for your input, Jay.

I don't think I'll be in the house long enough to see payback on a 90% model installation, but I have a question about the BTU requirement. Given that the house is poorly insulated, brick exterior, and about 1000 sf, does a 100,000 BTU furnace sound too large or about right? Also, should I demand a manual J from the contractors? Thanks!

I still say 90% is the way to go. You get a few credit here and there. Fed. Tex Credit, Local utility, gas utility, and from the brand themselves.

I would ask for the dealer to do a Manual-J on your home. 100k still seem awful big. 80k at the most.

Thanks again, Jay. It's becoming a nightmare with this project. :wall:Had two estimates so far - both from guys with good reputations. The first wanted to sell me a 100K 80% Rheem furnace and the bid for the job came in at $6300 with the attic ductwork. When I asked about that possibly being too big a unit, he said because the house is so drafty he wanted to get more heat into it more quickly. Now, that just sounds wrong to me, based on what I've read. He also said that the tax credits only apply for 95% afue units, and they start at over $4000.

The second guy hasn't submitted his price yet, but thinks I should mount the unit in the attic (which, again, sounds like not such a great idea in this area). At least he didn't think 100K was a good idea for this house. He said it would be more efficient up there, and the installation cost would be about the same as keeping it where it is.

The first guy said he didn't think my existing furnace could be flipped (even though it's designed for all three installations). The second said he thinks it could, if that's the way I want to go. If I'm not going to upgrade my 80% 75K unit to a high efficiency model, there doesn't seem to be much sense in replacing like with like, huh?

The info I'm getting is so disparate, I don't know who to believe at this point. If you have any other non-biased words of wisdom, I'd really appreciate it. Thanks!

I'm supposing you have your furnace in a closet on the main floor of your house?


Personally, I'd keep the furnace there rather than putting it in your attic.

Furnaces in attics and crawl spaces tend to get poorer maintenance because it's hard to work on the equipment.

Yeah, the existing furnace is in the back corner of the kitchen, and I walled it and the water heater in. I kind of felt the same about the attic installation. Thanks for the input. I hope you guys can enlighten me about the choices and which way might be best to go at this point.

Furnaces in attics and crawl spaces tend to get poorer maintenance because it's hard to work on the equipment.

Tell me. I have to go up through a ceiling, and fit between lights, wires and pipes, to get at one - that I don't think anyone has looked at in years, because of it's location. It amazes me it still even works. Last summer a/c condensate water was spilling though the ceiling from that unit and I had to remedy that.

Maybe more efficient in attic(per the one HVAC guy) because they can go to a cheaper open combustion furnace that will draw outside air into the attic, and not pull cold combustion air through your already drafty house.

So your existing Lennox 80 unit already is a downflow? Why can't that be used downflow in the attic, if say it is raised up in the air to allow the plenum/ducts to come out the bottom? Or is there a height problem, or something I'm missing, as to why that is impractical. I am not an installer - but there might be something to what I am bringing up.

Why is it that you are making the change?

If you do decide to go with an attic installation, stick with an 80% model. Condensing furnaces (90% & above) can be major headaches in an uncondioned attic. I've seen more than one secondary heat exchanger which froze & split.

Sorry to hear about your woes with the attic installation. That's exactly the kind of stuff I'd rather avoid, if possible. The reason I'm making the change is because my old ductwork is buried under the slab and in pretty bad shape. I heard about a company that has some kind of spray they can run through the ducts to restore them, but haven't been able to determine if it's legit or not. Sounds too good to be true. So, the only option is to run attic ductwork.

I've heard of sealing in-slab ducts but have never seen it done nor know of anyone who has had it done.

If you do decide to go with an attic installation, stick with an 80% model. Condensing furnaces (90% & above) can be major headaches in an uncondioned attic. I've seen more than one secondary heat exchanger which froze & split.

I didn't look to see where he is from. :eek: Yeah...that be true alright. And the entire condensate system could freeze...lines, traps, maybe a pump....everything.

And I have seen or heard of areas of the country be hit by hard freezes, say even once every 20 years or so, with temps you could never even imagine.

The attic I have to deal with is actually an enclosed conditioned one, so it does not get super cold up there.

Ummm. Well, the existing deteriorated ductwork makes a reasonable case for relocating the furnace.

Where IS the furnace located? What surrounds it?

De4pending on where it is, it might be worthwhile investigating a contractor who can repair it and find out what it might cost and get references to decide if you trust their methods and competence.

I'm not familiar with that procedure, but investigating it sounds like it might be worthwhile considering.

Yeah, the existing furnace is in the back corner of the kitchen, and I walled it and the water heater in. I kind of felt the same about the attic installation. Thanks for the input. I hope you guys can enlighten me about the choices and which way might be best to go at this point.

The furnace doesn't need repair, just flipping to updraft mode. It's the ducts that are the problem. I wouldn't mind replacing the furnace if I had to, but it wouldn't make much sense to replace it with another 80% model when this one works fine.

If you still have or can get the installation manual, I agree that flipping it would probably be your least expensive route. As I recall there are some furnaces which once converted to downflow there's no going back.