I have a house built in 1974. The gas furnace is original with the house and It needs replacement?

Question

Essentially this is a 1,296 SF home and the old furnace is a 65K btu furnace. I was told before replacing the furnace I need to do a load calcuation or calculate according the Manual J specifications. What is wrong exactly with using the OLD btu rating on the old furnace. Only things that have been really changed is a new door and some new 2nd floor windows.

Answer 1

Nothing, you should do fine going with what you got. BUT Keep in mind you may need to get this thing inspected. IF, you do they may have specific guidelines that will force you to go with whatever the guidelines say.

Answer 2

You can replace your old furnace with a 60,000 BTU, 90+ % model. You can also replace it with a 70,000 BTU, 80+ % model. Either one will handle your heating requirements. For cooling, if you wish to install central A/C, 30,000 BTUs should be fine.

Actually, if you were to get highly technical, smaller units might do the job, but the difference in price is minimal so having a tad more than needed won't hurt. Especially if you later added a bedroom or some other addition.

Good luck.

Answer 3

If by SF you mean San Francisco, then you are probable O.K. with a like btu furnace. It seems (Payne ) ships their furnaces for use at sea level and standard gas values. The problem arises at higher altitudes and different gas specific gravities and pressures then they must change orifices. Also, when I replaced mine (in the bay area) I was told that my air intake was a little too small for the newer fans my opening was 20" X 14" and it called for 25" X 14". I just changed the grill on the front to get more air and it works just fine. My house was built in 1974 and is 1200+ sq ft also. Mine is only 44k btuh which means it has two burners. Yours will have three burners each burner rated at 22k btuh.
Hope this helps.

Answer 4

As another poster suggested, get a couple companies to give estimates, and they if they are any good at all they will do a sizing on the spot with a laptop, for free.
The new furnace will be more efficient so it should be smaller than the old one, plus...the old one may have been sized too big in the first place.
Any energy efficiency improvements made over the years, like caulking, insulation, better windows, etc...will reduce the size you need. Don't get bigger than you need, it won't run as efficiently, and the up front cost is higher with no value added.

Answer 5

The system is 33 years old! You need to update the things that you were told (good, solid advice), as if you don't, you are staring catasptrophe in the face! Contractors (under law in most places) are bound to replace these things (just like the gas connectors on stoves when you get a new one). Get a couple of quotes from reputable heating and a/c contractors and go forward. DO NOT attempt to install the furnace or other specifications yourself unless you know what you are doing, and from your post, it doesn't sound like you do. Come one, the system and old specs have lasted 33 years. What more do you want!

Answer 6

get an estimate FREE. from at least 2 companys. The new furnace will be higher efficiency and not need as many BTU's. Your old unit might be 60% eff.. You'll save money in the long run or make your house easier to sell.

Answer 7

if you were comfortable this winter and in the past then 65k btu is fine.
i suggest that you contact your local gas utility for advice on the replacement.
they may have financing and other money saving programs available. seriously consider going with the new 90% plus efficient units -- it will pay for itself in just a few years

Answer 8

Just call a HVAC Contractor, have them do a load calculations just to confirm. You might also have to bring it up to code as well ,and make sure everything is ok. Get an estimate on replacing it, it will not hurt. Most company's do not charge for estimates.