I have a pole barn with an electric garage heater to keep it above freezing (I have it set to 40° F and the barn is insulated). Recently I had a major water leak (it didn't freeze, a connector was bad) and the barn was very damp for a couple weeks.

It could have been worse but there was a decent amount of damage from rust & mold. Since then, it seems like the heater is using a lot more electricity vs. last year when the temps go below freezing.

Looking inside the heater, it seems like the elements got a bit corroded. Will this reduce their efficiency? Should I try cleaning them with steel wool or something similar? Is there a way to test whether it's operating as it should?

It's not a terribly expensive unit but I'd like to be sure I need to replace it before wasting the time/money.

  • 2
    Stuff on the elements will make it work harder. If the elements are corroded/pitted, then it is time for new elements(hard) or a new heater. If just rust make sure you clean the connections also. Dirty/rusted connections will take more power, heat up, and burn up.
    – crip659
    Commented Dec 12, 2023 at 18:57
  • 8
    Depending on the extent of the water damage, insulation may have gotten wet. Solid foam board or similar won't be affected much. But loose (blown) insulation, fiberglass batts and other types will compress when wet but not expand when they dry out, lowering their effective insulating value. Commented Dec 12, 2023 at 19:47
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    Nobody ever complained that they had too much insulation.
    – KMJ
    Commented Dec 12, 2023 at 21:55
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    Do your stats have wind speed (and direction)? If more cold air is blowing in you'll lose more heat for the same value of "cold"
    – Chris H
    Commented Dec 13, 2023 at 16:36
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    Even if the insulation is not affected much: Residual moisture will cool the barn down. Some of the environmental heat (which the heater is contributing to) is used to evaporate water from the wood until the interior surfaces have reached their original dryness. That may take a while, if you think about how long it takes to dry fresh-cut wood until it is dry enough to use in a fireplace (months). And of course, as manasseh said, the moist wood contributes less insulation compared to the dry wood before the incident. Commented Dec 13, 2023 at 17:47

5 Answers 5


A resistive electric heater is very good at doing one thing: turning electricity in to heat. In fact, that's basically all it can do.

Corrosion in the heater might:

  1. Reduce the total heat output. If the resistance of the elements is increased, they will output less heat, but they will use less electricity at the same time.
  2. Cause failure, either due to a bad connection somewhere in the heater or a failure of the element.
  3. Smell bad.

There is no way for the electric heater to use electricity without turning it in to heat. Even the fan eventually makes heat by causing friction in the air. All the energy that goes in to the heater ends up as heat in the building.

A relatively small difference in climate might be causing significantly increased usage and costs, especially since you're not heating until very close to freezing.

  • All good info, thanks! As mentioned in a comment above, my electric company has an app that shows hourly/daily usage, avg temp etc. which makes it pretty easy to make historic comparisons. It subjectively feels not as hot when I'm standing under it while it's running but I'll collect another month or so of data & decide if I need to work on it.
    – Tobias J
    Commented Dec 12, 2023 at 21:35
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    If high resistance is resulting in lower heat output, it might be running longer while you feel less warm under it. The total heat output will be the same, but the experience of being heated by it will be different. If you want to validate if it's working before just replacing it, put a clamp ammeter on one of the power wires while it's running. If it's drawing the same amount of power as it's rated for, replacing it won't change the heat output. The only thing a replacement might get you is a different style of heating.
    – KMJ
    Commented Dec 12, 2023 at 21:55
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    A heater may produce radiant energy which would typically get converted into heat somewhere--perhaps in a location more useful than heat produced right at the heater itself. A radiant heater which is dirty may be produce its heat somewhere that's less useful and more apt to be distributed uselessly to the outside than one that's clean.
    – supercat
    Commented Dec 13, 2023 at 6:02
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    That heat still ends up in the building. It's not a change you're likely to notice over the much bigger variables of temperature and insulation, at least on a resistive heater. Dirt can be a bigger deal on heat pumps.
    – KMJ
    Commented Dec 13, 2023 at 6:37
  • @supercat's point is particularly valid for high ceilings with radiant heaters mounted up high (the heat then starts higher than the occupants, and it takes a long time for the air to warm enough that warm air is pushed down by even warmer air convecting), but that doesn't sound like what we've got here. That would also decrease the total power consumption unless the thermostat is down low
    – Chris H
    Commented Dec 13, 2023 at 16:36

While an electric heater is unable to turn electricity into anything else than heat at 100% rate, it is pretty much able to alter its efficiency in terms of heat distribution and thus to heat more objects and places away from the thermostat.

E.g. a radiative heater radiates most of the heat as infrared rays that are expected to heat the surfaces around more or less evenly, including surfaces physically below it. When the heater mirror gets rusty, less heat is radiated as infrared and more heat is carried away by convection, heating mainly objects above the heater, e.g. the ceiling.

If such a heater is thermostat-controlled, one will get the same temperature at the thermostat, but hotter ceiling, higher average temp over the room, higher electricity use and generally less personal heat comfort (cold feet).

Another factor increasing electricity use in your case may be the residual moisture in the walls that increases theit heat conductance and the room heat loss. The walls may need a lot more than "few weeks" in order to get completely dry.

  • 1
    Thanks for the additional insight, the residual moisture is something I hadn't considered & could definitely still be a factor
    – Tobias J
    Commented Dec 13, 2023 at 19:28
  • I had a frustrating discussion with ChatGPT over whether a TV is a 100% efficient heater as well. It couldn't make the connection between electricity inefficiently wasted as heat and heating efficiency still being 100%
    – user126527
    Commented Dec 14, 2023 at 12:26
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    @user126527 you can be equally frustrated talking with certain humans about the same subject.
    – fraxinus
    Commented Dec 14, 2023 at 21:13

If your barn is using more power for heating than last year, I doubt it is due to a heater damaged by water. But it might be wise to have the unit inspected to see if there is any water damage which would be a safety concern.

The heater might be running more than in the past because the damp barn will absorb heat as liquid water is converted to vapor. This is called the latent heat of vaporization.

Just continue to use the heater and see if it works OK. You are not taking any significant risk in trying it under observation. Surface corrosion on the heating element would not seriously affect performance. It would not cause the unit to use more electric power.

If water corroded the controls or the fan that could affect performance. If the fan is not as powerful as it was, then the heat would not be distributed as well and the unit might run more.

Unlike electric motors where electric power is converted to mechanical power, electric resistance heaters are all considered 100 % efficient because all the electric power is converted to heat which is the purpose of the appliance. There is no route that power can be "lost" to, if its intended purpose is to produce heat.


Heat is energy, energy can't be destroyed or created. Resistive heat appliances (vs. harvesting appliances like heat pumps) convert electrical energy to heat at 3142 btu's per kw/h. Doesn't matter if the appliance is a light bulb, TV, or some type of portable heater. You can't get more or less energy out than energy in. Take a look around Amazon some time looking for heat output of 1500 watt heaters. Numbers will vary a little for manufacturing tolerances and marketing, but all will be marketed at 5000 to 5120 btu's per hour.

If your heater is damaged and is using more energy it is putting out more heat. Checking current draw with an ammeter is a little difficult, you have to isolate one wire which usually means working in front of a hot electrical panel and turning the heater on and off. If your heater is a typical 120v plug in heater there are line splitters that allow testing at the plug, but you will almost never see one available retail.

The biggest effect of corrosion is it will change the ability of the element to dissipate heat. Usually corrosion does not make good surface contact and heat will build up at the point of corrosion and may destroy the element. The element isn't using any more energy or putting out more heat, it just isn't shedding it well.

If enough conductive build up is present and makes contact between elements or points on the element then a "short" current path can be created. A shortened path has less accumulative resistance, current will flow faster, will use more energy and will put out more heat until a breaker or other thermal protective device trips or the element itself burns up and opens the current path.

  • 1
    Thanks for the further explanation. I'm pretty familiar w/ thermodynamics but the concept of the heating elements not dissipating the heat as efficiently hadn't clicked yet. Appreciate all of the discussion on this!
    – Tobias J
    Commented Dec 13, 2023 at 19:31

Maybe the reason is not the heater, but insulation that just got worse performances because of remaining humidity. glass wool

It could be possible if the insulation is made with glass wool (if this is P.U., P.S. or wood wool that won't be normally affected by humidity) ; there is actually a lawsuit between french industries that revealed that under high level of humidity, glass wool insulation could lose up to 75% of its properties.

I could not quickly find an english reference about the lawsuit, except of these kind of imprecise articles (fr) [https://www.soigner-l-habitat.com/actis-vs-st-gobain-pourquoi-la-laine-de-verre-a-perdu-son-proces/]

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