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Main Question

I've already visited this similar, but different question and saw a commenter mention that about 500W seems appropriate for blower fan of an HVAC system. The past few months we've had high electricity bills compared to the same period last year (lived here 2.5 years), but it's also been a hot summer. I've plotted the kWh that have appeared on my statements (for science!); the increase begins in March.

Historical Usage

To try and investigate, I purchased "The Energy Detective" (TED) and have it connected to my condo's main power and also have a "Spyder" monitoring several individual circuits. Ever since, I have seen a constant draw of 1.7kW coming from my furnace.

Since it's summer and our system's fan is set to ON to improve circulation, I have to assume this is the blower fan's motor. When we're away at work or vacation and even I've made a point to power down everything that can be powered down, I still have the 1.7 - 1.8kW draw. Someone please check my math, but over 30 days, that 1.7kW load comes out to 1,224kWh. This amounts to about 1/2 of my monthly electricity bill, which was 2,550kWh last billing cycle (the previous year at the same time it was 1,290kWh).

This is way too much for a blower motor (or even the whole furnace, considering it's summer) to be drawing, right?

I realize this is a complex problem, so I've tried to include some relevant information below. Thanks for reading!

Other Info

I have contacted the utility company and they have verified my meter is accurate; they are also billing me for the correct meter (rather that one of my neighbors). My TED data is exactly proportional to their measurements (I must apply 1.5 factor to TED data to make it match utility's) due to the fact I've never bothered to calibrate it. I'm just realizing this means that blower fan may actually be drawing 1.7 * 1.5 = 2.5kW (or 1,830kWh per 30-day month).

My utility does provide the ability to view daily usage, and I've done this to verify my TED is accurate once the calibration is taken care of.

I live in a multi-unit building that was remodeled in mid-2000s; the HVAC is original to that remodel (so 10+ years old). I know some of the other units have had their heat pumps replaced. I have a service contract with a heating/cooling company to make semiannual maintenance visits. In February of this year they replaced the blower capacitor and charged $200 for it. March's bill is the first that begins to show significantly increased usage.

Not much has changed to my condo in the past year (same number of people, no remodeling, etc.) I did replace the water heater but that circuit is monitored separately by the Spyder and I can see it cycle on/off during the day. We have also purchased a portable AC unit (Honeywell MN10CES) for our 3rd floor, which gets very hot in the summer. The unit has a stated cooling wattage of 1,050W (verified accurate with Kill-a-watt).

The unit is only turned on when we are at home, and so wouldn't be a factor in that 1.7 (or 2.5?) kW load I see when we're away. It also doesn't run the compressor at night because the temperature naturally gets below the 78F setpoint. Even if that portable AC unit was actively cooling 24/7, it should only be about 750kWh.

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nabingham
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2 Answers2

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It is very unusual but not unheard of to have a furnace hooked up to a heat pump. Usually you would have an air handler and air handlers usually have backup electric heating strips. These heat strips Combined with the 300-400 watts from the blower could easily suck 1700 Watts. The strip heat should not be on when the fan is set to on and the temperature is turned down but it is not hard to miswire the unit. You should also verify the heat pump is not coming on too as this is not too hard to miswire either.

user76730
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Answering my own question because I've come to the conclusion that this level of power consumption is expected. The HVAC system has been inspected multiple times (regular maintenance and 1 service visit explicitly about the power consumption) with no issues found.

For additional info, this was a 1750 sq-ft condo with 3 levels. The first floor had 20 foot ceilings, and it's a corner unit with south and west-facing windows (which are maybe 100 years old). Also some leaky exterior doors, so I fully expect the unit to be working overtime to try and keep a reasonable temperature.

Also, I've moved, and the new house (single family, 5 bedroom, new construction) has similar electrical consumption from its blower motor.

nabingham
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