1 kW·h per hour just running fan

[david8370]

Is it possible that just running the fan on my furnace is using 1 kW·h per hour? Last night before I went to bed, I checked the meter and let the fan run all night. To my surprise, 8 hours later the meter moved 8 kW·h.

I know we have other appliances that draw some energy when they are off (DVRs, computers, etc.), but I was surprised by this.

If it consumes this much energy just to run the fan on my furnace, I may end that practice altogether. :eek2:

[heaterman]

Would depend, I normally figure .5kw per 24 but all electric using devises can vary. You got a fridge, hot water tank, security lights etc.? Turn off the blower and check it tonight.

[BaldLoonie]

A gas furnace blower motor may run around 700-800 watts so you could round that up to 1 kw per hour. A VS blower running 1/2 speed for constant fan runs under .1 kw per hour by comparison. You may be surprised at how many items in your house are drawing power when off too.

[david8370]

Would depend, I normally figure .5kw per 24 but all electric using devises can vary. You got a fridge, hot water tank, security lights etc.? Turn off the blower and check it tonight.

Thanks. I'll give it a try tonight without the blower on and see what the difference is.

[beenthere]

If you have an electric water heater, it may have come on.
Your refrigerator most likely ran during the night.

[Luis-Pasco]

Thanks. I'll give it a try tonight without the blower on and see what the difference is.


You would be surprised to see what your other appliances are using electricity wise. I just went through this in my whole house.

[Home&Marine]

A 1.5 hp motor is 1.12 Kw! I'm actually surprised that you didn't consume more than 1 kw a night considering computers, HotWater, TV's and wall warts. In most all new TV's the power supply is hot constantly.

[david8370]

.. edit

[david8370]

If you have an electric water heater, it may have come on.
Your refrigerator most likely ran during the night.

I don't have an electric water heater, but how much would a typical side by side use an hour do you think?

[david8370]

A gas furnace blower motor may run around 700-800 watts so you could round that up to 1 kw per hour. A VS blower running 1/2 speed for constant fan runs under .1 kw per hour by comparison. You may be surprised at how many items in your house are drawing power when off too.

My furnace is the Rheem RGRL-90. Can't find anywhere in the documentation how many watts it uses... I know it depends on a lot of things. The fan setting is on low, where I'm at about 1035 cfm based on my ESP.

http://globalimageserver.com/fetchDocument.aspx?id=c43a1928-2015-4fb2-9d4b-ef31233d6cbf

[beenthere]

I don't have an electric water heater, but how much would a typical side by side use an hour do you think?
I'd guess several hundred.

[Home&Marine]

Per you info sheet, your blower is a 3/4 hp so the watts should be 560. I'm still thinking you're about where you should be. I haven't checked my Kw cost today but it was 8 or 9 cents a kw/h last time I looked (several years ago).

Going back to your sheet, they list the motor as 3/4 hp and then [559]

MOTOR H.P. [W]– SPEEDS–TYPE 3/4 [559]-4-PSC (copied and pasted from the sheet)

[david8370]

Per you info sheet, your blower is a 3/4 hp so the watts should be 560. I'm still thinking you're about where you should be. I haven't checked my Kw cost today but it was 8 or 9 cents a kw/h last time I looked (several years ago).

Going back to your sheet, they list the motor as 3/4 hp and then [559]

MOTOR H.P. [W]– SPEEDS–TYPE 3/4 [559]-4-PSC (copied and pasted from the sheet)

Thanks. Does that 559 hold even if it's on the low blower speed?

[beenthere]

I believe you'll find that the watt listing isn't the wattage the motor draws. But rather a watt rating to indicate its HP.

Simular to the KW rating of A/Cs in other countries.

Converting a motor horse power to KW, 1 HP=.746KW.
746watts times .75=559.5

So in your motors case. A 559 watt motor, is a ¾HP motor.

Since motors are not 100% efficient. Your operating watts could be 690 to more then 700 watts, depending on your duct work.

[david8370]

I believe you'll find that the watt listing isn't the wattage the motor draws. But rather a watt rating to indicate its HP.

Simular to the KW rating of A/Cs in other countries.

Converting a motor horse power to KW, 1 HP=.746KW.
746watts times .75=559.5

So in your motors case. A 559 watt motor, is a ¾HP motor.

Since motors are not 100% efficient. Your operating watts could be 690 to more then 700 watts, depending on your duct work.

Thanks, BT. You certainly know your ****. :yes:

[Home&Marine]

Thanks. Does that 559 hold even if it's on the low blower speed?

I would guess about 1/2 to 2/3's (of the 559). Some one that knows the unit better can probably say for sure.

[docholiday]

The 559 is the max watts. At low speed it would be lower. Without a fan performace curve and airflow data from your actual blower, the only way to know your watts is simply a measurement of Volts x Amps (with the blower door on). As an example, let's say the voltage at your furnace when running is 121 vac. The measured current to the furnace with just the fan on measures 4.25 amps. You would simply multiply and find a wattage of 514.25. You wouldnt want to measure the current of only the fan, rather the whole furnace since there is power used for the control ciruit too.

Your outdoor unit, while off may have a crankcase heater pulling in the neighborhood of 40 watts. Your refrigerator? Who knows, depends on its size, age and load. remember a frost free fridge has door heaters too.

[Adnshel]

Did you ever see how much your house pulled without blower running?

[Carnak]

Since motors are not 100% efficient. Your operating watts could be 690 to more then 700 watts, depending on your duct work.That is pretty much the VA draw the NEC says to assume for a 3/4 Hp under a full load

[david8370]

Did you ever see how much your house pulled without blower running?

No, I haven't gotten around to it yet. My wife has a cold and has been snoring, so I leave the blower on to create a little white noise. :LOL:

I'll experiment with it next week.

[Adnshel]

That's pretty funny.