Gas and Oil Home Heating Furnaces - Manual J says go smaller
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Detroit Heat
08-29-07, 03:45 AM
After getting a whole load of quotes for a new furnace and AC I
think I have selected the contractor I think I want to do my work. Problem is, he seems to think I can get away with a 20k btu smaller furnace??
Heat loss from his manaul J is 64,000 BTU. We took out a 25yr old 100k furnace that did a good job. We are installing a 90+, 2 stage, variable speed, 80k btu. He says the effeciency gain over the old will make up for the smaller BTU's. Everyone else quoted 100k btu (he is the only one that showed me a manual J calc though)
I live outside detroit, 2 story, stick construction, natural gas, 1900 sq ft. (half upstairs, half downstairs), insulated attic, full cement basement, typical windows for a house this size.
Does the Manual J calc sound in the ballpark? Can the efficieny really make up for a smaller heat output?
think I have selected the contractor I think I want to do my work. Problem is, he seems to think I can get away with a 20k btu smaller furnace??
Heat loss from his manaul J is 64,000 BTU. We took out a 25yr old 100k furnace that did a good job. We are installing a 90+, 2 stage, variable speed, 80k btu. He says the effeciency gain over the old will make up for the smaller BTU's. Everyone else quoted 100k btu (he is the only one that showed me a manual J calc though)
I live outside detroit, 2 story, stick construction, natural gas, 1900 sq ft. (half upstairs, half downstairs), insulated attic, full cement basement, typical windows for a house this size.
Does the Manual J calc sound in the ballpark? Can the efficieny really make up for a smaller heat output?
mattison
08-29-07, 05:26 AM
Normally yes. You're getting to use 90+ percent of the heat made in the furnace now as apposed to 80% or less from the old furnace. Besides that I'm sure that in the last 25 years there have been updates to your home to conserve energy.
Jay11J
08-29-07, 07:36 AM
I agree with Matt.
I live in a 1968 split level home, I had a 115,000 BTU, and went to a 60,000 Two stage furnace..
It had NO trouble at all keeping up with our -20˚ winter we had, and most of the time it ran 1st stage, and 2nd when it got below -0˚.
Be sure you get a two stage t-stat.
I live in a 1968 split level home, I had a 115,000 BTU, and went to a 60,000 Two stage furnace..
It had NO trouble at all keeping up with our -20˚ winter we had, and most of the time it ran 1st stage, and 2nd when it got below -0˚.
Be sure you get a two stage t-stat.
Detroit Heat
08-29-07, 08:04 AM
Thanks for the warm fuzzy.
After I posted, I went back through the old posts and found a bunch of what Jay posted, somehow, I figured he would be OK with what I had planned!
Thanks for your posts Jay, Matt, they gave me a lot more confidence in my selection.
I will let you know how everything turns out.
After I posted, I went back through the old posts and found a bunch of what Jay posted, somehow, I figured he would be OK with what I had planned!
Thanks for your posts Jay, Matt, they gave me a lot more confidence in my selection.
I will let you know how everything turns out.
Jay11J
08-29-07, 08:23 AM
Glad to hear you feel at ease going smaller.. As they say, "Going bigger isn't always good!"
furd
08-29-07, 11:43 AM
One thing that you will notice is that the new furnace will run for a longer period of time than did the old. Not to worry because the new furnace will be burning a lot less fuel and the temperature within the home will be more even and comfortable.