LBrown59
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A 100000 BTU furnace or air conditioner or a 50000 BTU furnace or air conditioner?
which one would use the most energy?
- Thread starter LBrown59
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wushaw
Elite Member
The one with the highest amp rated fan/blower motor
robison
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Which will use the most energy? It depends upon the load.
If both run 100% of the time, the one that's twice as big will use twice as much energy.
If the load is 25,000 BTU the small unit will run 50% of the time where the big unit will run 25% of the time. The bigger unit will use more energy because it will start and stop twice as often. The unit is least efficient during startup and warmup so you want to keep cycling to a minimum.
If the load is 75,000 BTU the small unit won't be able to keep up so efficiency will not matter.
If both run 100% of the time, the one that's twice as big will use twice as much energy.
If the load is 25,000 BTU the small unit will run 50% of the time where the big unit will run 25% of the time. The bigger unit will use more energy because it will start and stop twice as often. The unit is least efficient during startup and warmup so you want to keep cycling to a minimum.
If the load is 75,000 BTU the small unit won't be able to keep up so efficiency will not matter.
slowrev
Elite Member
Depends on what kind of energy you are talking about.
BB_TX
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Disclaimer: This is just my opinion and have no experience to back it up.
Assuming the 50,000 unit is adequate to heat/cool the area, there will probably be little difference.
If the 100,000 unit took 5 minutes to heat the area, the 50,000 unit should take about twice that long.
The area would cool at the same rate with either unit, so assuming it cooled to the set point of the thermostat in 30 minutes, the 100,000 unit would cycle every 35 minutes, the 50,000 would cycle every 40 minutes. The 50,000 would cycle less often, but run twice as long.
Assuming the EER was the same for both, the operating costs difference would probably be negligible.
If the 50,000 unit was marginal for the area, there may be times when it could never catch up and might run continuously. On the other hand, if the 100,000 was way overkill for the area, it may use more energy in the cycling on/off.
Just my $.02 worth. Now an expert can shoot holes in my theory /forums/images/graemlins/smirk.gif
Assuming the 50,000 unit is adequate to heat/cool the area, there will probably be little difference.
If the 100,000 unit took 5 minutes to heat the area, the 50,000 unit should take about twice that long.
The area would cool at the same rate with either unit, so assuming it cooled to the set point of the thermostat in 30 minutes, the 100,000 unit would cycle every 35 minutes, the 50,000 would cycle every 40 minutes. The 50,000 would cycle less often, but run twice as long.
Assuming the EER was the same for both, the operating costs difference would probably be negligible.
If the 50,000 unit was marginal for the area, there may be times when it could never catch up and might run continuously. On the other hand, if the 100,000 was way overkill for the area, it may use more energy in the cycling on/off.
Just my $.02 worth. Now an expert can shoot holes in my theory /forums/images/graemlins/smirk.gif
Egon
Epic Contributor
Don't think there is real positive answere unless a design/ sizeing process is gone thru. All else is just guesswork! /forums/images/graemlins/grin.gif
Egon /forums/images/graemlins/grin.gif
Egon /forums/images/graemlins/grin.gif
midlf
Platinum Member
Not a professional but this is my understanding: Correct sizing is the key. You don't want a 100kbtu ac if the 50kbtu will do. The 100 would overcool the air without stripping out the moisture. This is not comfortable. If anything the AC should be a bit undersized. On the hottest day of the year the AC should not shut off and should, just barely, not make the set temperature. On the coldest windiest day the furnace should shut off briefly after a long long run. This should give you the most economic system for a given unit efficiency.
slowrev
Elite Member
One thing I do know for a fact. If you use too big of an air conditioner and live in a humid climate you will grow mold and such in your house. The big air conditioner will not run long enough to remove moisture from the air and you will have a damp cool house. Not a good thing.
Sizing is important both in heat and air, but especially in AC. ductwork sizing must be matched to the furnace/AC as well for efficient and proper operation.
For the most efficient system it should be sized and laid out by a pro. Right sized duct, returns and heating size/cooling size.
Ben
Sizing is important both in heat and air, but especially in AC. ductwork sizing must be matched to the furnace/AC as well for efficient and proper operation.
For the most efficient system it should be sized and laid out by a pro. Right sized duct, returns and heating size/cooling size.
Ben
