# Why would an electric furnace use so much energy? **URL:** \ **Category:** Factual Questions\ **Created:** [October 21, 2016, 8:32pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276 "2016-10-21T20:32:50Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 8:32pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/1 "2016-10-21T20:32:50Z")
I have one of those gizmos that shows how much electricity our house is using at any time. We have electric heat. Last winter, when our furnace kicked in, we’d jump up to 11, 12, or sometimes 13 kw/h, for the few minutes it was running. When it stopped, we would revert back to whatever we were at before it started up - from less than one to more than 3 or so kw/h, depending on what else in the house was running. Now, we have the furnace turned on again and when the furnace kicks in, it’s up to 24 kw/h. When it stops, it’s back down to what it was before, just like last year. So, my question is why would the furnace be using twice the energy than it used last year? What could be causing such a jump in the amount of electricity we’re using? Something about the furnace? It sounds the same as it did last year. The fan part worked a little this summer when we ran the A/C a couple times. No problem. Any ideas? ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [October 21, 2016, 8:39pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/2 "2016-10-21T20:39:26Z")
Step 1: is the gizmo accurate? I’d look at the heating elements to see if any are broken or shorted. It may take a pro to safely check them when it’s operating. Just possibly there are two heating elements, and only one was kicking in during your former measurements and both are now - is it colder? Do you have the heat turned higher proportional to the current ambient temperature? Other than that, got no ideas… except that electric heat really as a choice. Most of the units date from 1950-1970 when nuclear power was going to make electricity dirt-cheap. We had friends who bought a house in an “all electric” subdivision… and ca. 1990 they tore up the streets to lay in natural gas to every house. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 8:58pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/3 "2016-10-21T20:58:42Z")
I wondered about the gizmo that all the data comes from, but I can’t think of a reliable way to test its accuracy. I’ll think on it. Difference in temperature is irrelevant, I think, because the furnace is either on or off. Whether it runs for a minute or ten minutes, it draws energy at the same hourly rate. I may have to have the heating elements checked for a short, I guess. ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [October 21, 2016, 9:02pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/4 "2016-10-21T21:02:39Z")
Look at the manual for your electric furnace (if you can’t find it look online for it or other information). There may also be an information plate on the furnace. One of these should tell you the watts the furnace produces. How does this compare to your measurements? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 9:16pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/5 "2016-10-21T21:16:07Z")
Your units are confused. KW is the amount of power the furnace is consuming. KWH is the amount of energy it used over a specific time period. What does the gadget measure? Instantaneous power, or totalized energy? If it’s the latter, and it is running for twice as long, the reading will be twice as high. If it’s the former, the reading should be the same. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 9:20pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/6 "2016-10-21T21:20:32Z")
It reports in kw/h. In other words, you’re using energy at that rate. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 9:32pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/7 "2016-10-21T21:32:05Z")
> [@CC](#): > > It reports in kw/h. In other words, you’re using energy at that rate. That doesn’t make any sense. KW is already a rate- 1000 Joules/second. KW/H is like saying 24 MPH/minute. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 9:34pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/8 "2016-10-21T21:34:36Z")
One can travel at a rate of 24 mph for a minute. ---
**Author:** ![Do\_Not\_Taunt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/do_not_taunt/32/2968_2.png) [@Do\_Not\_Taunt](https://boards.straightdope.com/u/Do_Not_Taunt)\ **Post date:** [October 21, 2016, 9:34pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/9 "2016-10-21T21:34:58Z")
To put it another way, kw is not a measure of energy. (It’s a measure of power, which is energy per unit time.) So kw/h is not energy per hour, it’s “power” per hour, which isn’t a measurement that really makes much sense. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 9:37pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/10 "2016-10-21T21:37:19Z")
> [@CC](#): > > One can travel at a rate of 24 mph for a minute. Right: 24mph\*m Hence KWH, not KW/H ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 9:40pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/11 "2016-10-21T21:40:38Z")
> [@Do\_Not\_Taunt](#): > > To put it another way, kw is not a measure of energy. (It’s a measure of power, which is energy per unit time.) So kw/h is not energy per hour, it’s “power” per hour, which isn’t a measurement that really makes much sense. To really be pedantic about it, KW/H would be the rate of change of the power usage. Just like acceleration is in m/s/s. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 9:45pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/12 "2016-10-21T21:45:01Z")
Ok…whatever…the readout changes as energy use changes. Regardless of the correctness of my terminology, something appears to be different this year - and it seems to be more electricity use under identical conditions. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 10:03pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/13 "2016-10-21T22:03:09Z")
Calibrate your gadget by turning off all the loads you can, and then running a known load, like a hair dryer. Also, are all the other reading reasonable? Check the current transformer for the furnace circuit. ---
**Author:** ![Do\_Not\_Taunt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/do_not_taunt/32/2968_2.png) [@Do\_Not\_Taunt](https://boards.straightdope.com/u/Do_Not_Taunt)\ **Post date:** [October 21, 2016, 10:18pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/14 "2016-10-21T22:18:02Z")
> [@beowulff](#): > > To really be pedantic about it, KW/H would be the rate of change of the power usage. > Just like acceleration is in m/s/s. I understand that. My point is that the number of times in my life I’ve needed to measure rate of change of power use is zero. Perhaps specialists need this occasionally? I don’t know. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [October 21, 2016, 10:28pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/15 "2016-10-21T22:28:20Z")
> [@beowulff](#): > > Calibrate your gadget by turning off all the loads you can, and then running a known load, like a hair dryer… Excellent idea. I did just that. First, though, I ran the hair dryer through a Kill A Watt to check its exact draw - 1200 watts - and then ran it and looked at the energy monitor that I was calibrating. It reflected exactly the power rating in watts of the dryer. The reading jumped exactly 1200 watts. It leads me to believe that the problem is with the furnace. (And, yes, the reading is in Kw, not Kwh or Kw/h. :o ) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 21, 2016, 10:31pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/16 "2016-10-21T22:31:18Z")
I don’t see how the furnace could be pulling 2x it’s normal load. 24KW is 100A at 240V. How big is the furnace breaker? ---
**Author:** ![Common\_Tater](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/common_tater/32/13846_2.png) [@Common\_Tater](https://boards.straightdope.com/u/Common_Tater)\ **Post date:** [October 21, 2016, 10:52pm UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/17 "2016-10-21T22:52:42Z")
Assuming the energy calculations are correct, to draw twice as much current all things being equal may point to an electric motor fan on its last legs? They will start to draw lots of current before they lock up. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 22, 2016, 12:13am UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/18 "2016-10-22T00:13:54Z")
It’s hard to see how this could even be due to a malfunction in the furnace. If the furnace is consuming that much electrical energy, then it’s producing that much heat, period. If it’s consuming more, then it’s heating more. A malfunction could do something like producing heat in a dangerous location, but it can’t just make heat disappear. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 22, 2016, 12:24am UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/19 "2016-10-22T00:24:27Z")
> [@Common\_Tater](#): > > Assuming the energy calculations are correct, to draw twice as much current all things being equal may point to an electric motor fan on its last legs? They will start to draw lots of current before they lock up. Very doubtful. 24KW is a huge amount of power - 50% of the rated power of my breaker panel. Any fan drawing that much power would be incandescent. ---
**Author:** ![Common\_Tater](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/common_tater/32/13846_2.png) [@Common\_Tater](https://boards.straightdope.com/u/Common_Tater)\ **Post date:** [October 22, 2016, 12:59am UTC](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276/20 "2016-10-22T00:59:20Z")
24KW is the current (heh) **total** consumption _now_, previously about half that. Even half is considerable, agreed. But there isn’t anything else that I’m aware of that could contribute to a higher energy draw. [Next page](https://boards.straightdope.com/t/why-would-an-electric-furnace-use-so-much-energy/769276.md?page=2)