Heating, Air Conditioning, Fridge, HVAC/Furnace replacement

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Question
Hi Fred, Thanks for your service. I live in N/W Indiana and wonder if you can help.
We want to replace an old Furnace in my sons duplex with a new one. I had good luck with Goodman so I will buy one. The problem is sizing, the old unit was a Armstrong mod G63A-80  80000 BTU input and 64,000 BTU bonnet cap,& it supplied lots of heat but it's old and I don't want to replace it in the winter.  I have no idea what the efficiency is.(65-70%??) The duplex is maybe 80 Years old and has  about 1000 sq' in each apartment.
(with 600 downstairs and 400 upstairs)
In the unit next door (about the same size)I replaced it years ago with a Goodman 7000 BTU furnace which is plenty big enough.
When I tried to order the 70,000 single stage up flow furnace, i was told that it has been replaced by either a 60,000 or 80,000 BTU unit. Since it is a rental,I am buying only a 80% efficiency model. I read somewhere to go by Bonnet cap. in which case I don't want to over rate the furnace and go with the 80,000 unit.  Do you think that the 60,000 BTU unit will work ?? Both apartments have a common wall so some heat will migrate from one to the other. Thanks Juergen

Answer
Juergen:

It's quite common today to provide a 40MBH furnace for a 3,000SF two story detached home (new construction) here in Sussex County, DE (Design 18F). How does that extrapolate to a 1,000SF, 80 yo semi-detached in NW Indiana (Lafayette 3F design)? Good question.

Regrettably, I can't answer: I signed on here to help homeowners, not businesses or investors (especially investors who don't care what heat costs their tenants in such a cold climate).

Fred

Heating, Air Conditioning, Fridge, HVAC

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Fred Weldin

Expertise

I can't help you if your whatsis won't work, people (Especially if it's a refrigerator); I have no experience with appliances, and I haven't been involved with H&AC service and repair since March 08, 1996 (Thank the Lord); I always send a "standard" reply to appliance questions and H&AC "Service and Repair" questions (about 20 a month), so if you want to know why your whatsis isn't working like it used to, ask someone else. A lot of my answers arenít read by the questioners; in that event, I always send reminders to read the answers for a month or more (the word "idiots" comes to mind - actually there's another more appropriate word, but discretion prevents its use here). If you have questions about how big a unit you need, if one room's warmer than the others, if you want an opinion oas to scope of work on bids received, etc. just ask. Do visit www.askweldin.com, there's a lot of good information on sizing, ductwork, efficiency, as well as some techniques accomplished DIY-ers can use to troubleshoot and improve their H&AC. Finally, I want to thank all of the kind, serious people whom I meet here: I enjoy working with you. My wife says I'm "snarky" from time to time; as for you others, please use your imagination as to the responses swirling on the snarky side of my brain when I read your questions.

Experience

53 years in the business. See www.askweldin.com

Organizations
ASHRAE, ICC.

Education/Credentials
B of ME U of D 1965, numerous classes, seminars and a lot of "Hands On" learning since.

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