SKINNER
Well-known member
Can a heater be too big? I have calculated my heater needs to be 150,000btu's for the coldest day Southern Indiana sees. If I were able to purchase a 250,000btu heater for a fair deal would there be any negative effects?
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Need Answer Quick, Heater too big?
- Thread starter SKINNER
- Start date
PAToyota
Well-known member
A/C units can be too big - in that their cycle time is too short. Just as everything gets up to operating capacity it shuts down because the temperature has already been reached. A fuel furnace can have similar issues. Basically that there is an efficiency that is reached only after the unit has operated from some period of time. If the cycle time is less than that, it never reaches efficiency. Sort of like only taking very short trips in your car. This would not be as much of an issue with electric heat.
Skinner, it really depends on how much yout in and out. A garage is not like a house. A garage door may be 75% or one wall and the amount of air turned over when you open it is significant. a 250K in that respect is not going to be oversized if yoyuu are using the garage as a garage. It will bring the temp back up quicker. But one it's up, it can tend to short cycle. Mounting the thermostat away from any area of moving air (but not in an enclosed space like a cabinet) will help eliminate this. One possibility is to use a stat lock cover. These are the little boxes you see in schools and businesses that cover the thermostat and keep people from changing it. It will slow the air movement to the stat and allow it to cycle with a more reasonable timespan.
HoosierBuddy
Well-known member
I got to this post late, but I see a couple of downsides...though not what I'd call showstoppers.
If it's a natural gas heater, you need to look at the pipe size requirement for a 250,000 btu hour per load and insure that you can do that in a feasible way. I'm guessing it would have a 3/4" or 1" inlet, but depending on the length of the run, you might have to use larger pipe. In Evansville, you'd be on Vectren South. I'm pretty sure they supply you with 7 inches w/c gas supply. Your meter is likely rated for about 275,000 total BTU's per hour...so if you notice your house's furnace doesn't want to run right, you'd need to call Vectren and ask them for a bigger meter.
You are also going to have to supply a larger flue. If it's a B-vent...it might be what? 6" Diameter? Is that a problem for where you are going to install it.
The other issue would relate to efficiency. An 80% efficient 250,000 btu furnace wastes 50,000 BTU's per hour. At today's gas rates, that's about 60 cents per hour of burner time out the flue. The burner will run less than a smaller furnace, evening it out some...but I know my house used to have KILLER gas bills before I jerked out the 250,000 BTU furnace and put a 125,000 BTU furnace in its place.
The other thing I was going to point out is this. If you are only going to run it when you are out there, and can get the gas line you need and the flue you need...and the price is right, I don't see anything wrong with the idea. If you are going to be running it all the time, I'd suggest going with a new high efficiency furnace. It'll pay for itself rather quickly.
Good Luck!
Phil
If it's a natural gas heater, you need to look at the pipe size requirement for a 250,000 btu hour per load and insure that you can do that in a feasible way. I'm guessing it would have a 3/4" or 1" inlet, but depending on the length of the run, you might have to use larger pipe. In Evansville, you'd be on Vectren South. I'm pretty sure they supply you with 7 inches w/c gas supply. Your meter is likely rated for about 275,000 total BTU's per hour...so if you notice your house's furnace doesn't want to run right, you'd need to call Vectren and ask them for a bigger meter.
You are also going to have to supply a larger flue. If it's a B-vent...it might be what? 6" Diameter? Is that a problem for where you are going to install it.
The other issue would relate to efficiency. An 80% efficient 250,000 btu furnace wastes 50,000 BTU's per hour. At today's gas rates, that's about 60 cents per hour of burner time out the flue. The burner will run less than a smaller furnace, evening it out some...but I know my house used to have KILLER gas bills before I jerked out the 250,000 BTU furnace and put a 125,000 BTU furnace in its place.
The other thing I was going to point out is this. If you are only going to run it when you are out there, and can get the gas line you need and the flue you need...and the price is right, I don't see anything wrong with the idea. If you are going to be running it all the time, I'd suggest going with a new high efficiency furnace. It'll pay for itself rather quickly.
Good Luck!
Phil