3

My understanding is that convection electric baseboards use electricity to run current through a resistor, which generates heat. My understanding is that this should be fairly efficient in the sense that the electrical energy is efficiently converted to heat.

However, it may still be inefficient because electricity needs to be generated and transmitted to the home.

I have recently learned about hydronic electric baseboards. They presumably use resistors to heat mineral oil in the unit. I am told these units are more energy efficient.

My question is: why? I can see that the mineral oil will take some time to heat up, and some time to dissipate the heat, creating a slower/more continuous supply of heat to the room. But why would this be more energy efficient?

5
  • 4
    If you want to compare efficiencies, you have to be careful you're comparing apples to apples. Electrical power can be turned into heat with 100% efficiency (because heat is the ultimate fate of all power, whether we like it or not). The goal of home heating equipment is not just to create heat but to create it in a way that creates a safe, comfortable living environment. To the extent these resistive heating systems have different efficiency, it is in creating such an environment - not merely in converting electricity into heat. Jul 7 '21 at 12:54
  • Good point. I think what you're saying is probably at the heart of what makes convection resistive heating relatively inefficient. I'm wondering why hydronic baseboards would be more efficient in converting that same heat energy into a more comfortable environment. Jul 7 '21 at 13:29
  • Great question! Lots of hits on Google saying they are more efficient, but as near as I can tell no one has actually done the experiment.
    – LShaver
    Jul 7 '21 at 14:36
  • There are also heat pumps with >100% efficiency. Compared to those, electric heaters are inefficient.
    – user253751
    Jul 28 '21 at 10:30
  • 1
    I wonder whether temperature and heat distribution is the key here. Heaters don't just generate heat, they heat something. For convective heaters, that's air. So a heater that also heats the wall behind it will be less efficient than one that just heats the air in the room. And a hairdryer will be less effective than a radiator that produces a gentle draft of slightly warm air.
    – Móż
    Sep 1 '21 at 0:37
2

Thermodynamic Efficiency

Hydronic electric baseboards are not any more thermodynamically efficient than convection electric baseboards. One watt of electricity fed through a resistive heating element produces one watt (3.412 BTU) of heat. It doesn’t matter if you use a simple resistor, fill the cavity with oil, or stack rocks on top, it’s the same amount of heat.

Heating Comfort

The difference, as Jean-Paul points out is the comfort level in the room. Simple resistive heaters heat a space quickly, which is great if the room is cold to begin with, but once it reaches desired temperature they must cycle on and off to maintain it, which may not be desirable depending on how close you are sitting to the heater.

Oil-filled units take advantage of a feature called, “thermal inertia.” It takes longer to transfer the electric heat into the room, slowing down the temperature rise, but once the unit cycles off, the oil continues adding smaller amounts of heat so the room cools slower as well. Some people find this more comfortable.

Makers of oil filled electric heaters try to bill this change of how the heat feels as an incentive to set your thermostat lower, and frame it as an efficiency increase, it isn’t, and at the end of the day, if it’s 40 degrees outside and your room is set at 70, the exact same amount of BTU’s, and watts per hour will be needed to keep this temperature differential. So an oil filled 1500 watt heater produces 5118 BTU’s, exactly the same as the simple 1500 watt electric strip. The efficiency is the same.

Power line losses

There are indeed losses in power line transmission as you suggested, but these are not evident in your electric usage since the meter is on the side of your house, downstream of all the transmission lines. Transmission and distribution losses in the United States are estimated at 5%. While your heater might be using 1500 watts, and your electric meter is accurately tracking it as such, the power plant might have to produce 1580 watts to make it run, with the remaining 80 watts heating lines between you and the power plant.

Natural gas heating costs

Natural gas and other fossil based fuel heating systems have losses too, but the end cost of these fuels “per BTU” is generally far less than electricity, this lower cost usually more than offsets the heating system losses in the home. As always, your mileage may vary.

2

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.