Does an electric heater lose efficiency if the elements are rusty/corroded?

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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

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/]