Space Heaters

Posted by on Dec 2, 2011 in Electrical, Heating | 30 comments

One of the most misunderstood elements of our house is the way that it will be heated.  Many people read the quote that it could be heated with two space heaters as it would.  Obviously, this led to a great deal of consternation, confusion and derision.  Aside from the fact that I don’t think it’s even possible to get approval from the city for something like this, it would be extremely expensive to heat even our house with electricity*.

Holmes Space Heater

NOT our new heating system

The difference between gas and electrical resistance heat is large here in Minnesota.  Gas is sold in therms, which represent 100,000 BTUs of energy.  A therm is 78 cents in Minneapolis.  Assuming that the combustion device is 90% efficient, that means you get 90,000 BTUs of useable energy for less than a dollar.  Electricity, on the other hand, is measured differently.  It’s sold in kilowatt-hours (kWh), at about 10 cents a kWh.  A kilowatt-hour of electricity can be completely converted to heat (there’s no ‘waste’ in the process), resulting in 3,413 BTUs.

Put simply, this means that 1,000 BTUs cost less than a penny (.86 cents) if you burn natural gas, but almost 3 cents if you use electricity.  Even more simply, electricity costs 3 1/2 times as much to heat with than natural gas.

Cost is not the only reason to heat with something other than electricity.  Consider that electricity is very ‘dirty’ in most parts of the country.  Why?  Because it’s generated by burning coal.  Also, while converting the electricity that arrives at your house to heat is 100% efficient, the transfer of power to your house is not.  Transmission losses average 7% in the United States, putting electrical efficiency roughly equivalent to a high efficiency gas condensing boiler or water heater.

All of that said, space heaters make for an excellent short term solution until the heating system is installed.  Our house is about 60% insulated at this point, which means we have exterior walls with an R-value of about R-35.  It’s not quite airtight, as the new front door is not installed and the access panel to the attic has not been sealed.  We’re not to where we need to be, but it’s pretty good for a house in progress.  A heater on the first and second floor running on low (900 watts draw each) will keep the house in the mid-60s.  Not bad.

An example of how easily the house can be heated: this morning I came downstairs to an unheated first floor, after a nighttime low of 15F.  The thermostat on one of the heaters sometimes resets to its lowest setting (45F), which is inconvenient.  I turned on the heater, and in about 15 minutes, it had warmed almost 1,000 square feet to 62F.  I can’t wait to see how the house performs when it’s actually fully insulated, tuned and ready to go.

* Note that when I say heat with electricity, I’m referring to electrical resistance.  Air-to-air heat pumps, geothermal ground loops and other technologies technically use electricity to generate heat, but via a completely different mechanism.

30 Comments

  1. Nicely put. Thanks for presenting this so clearly and effectively.

  2. Hey Paul, great project and thanks for the blog. I saw Tim’s presentation on the project at the PH Conference, and was inspired. Regarding electric transmission losses, I don’t think 7% tells the whole story: to quote from Marc Rosenbaum’s blog, “Overall, depending on the mix of power generators in a region, the generally-accepted figure for the US power grid is that about two thirds of the energy that goes into the powerplant is lost before it gets to us at our homes.” In addition to resistance losses, there are other transformers and such between power plant and house, and there are big losses electricity production (think of the plumes of smoke and steam–lost heat=energy).

    • Tom, I’ve read of transmission loss estimates around 70%, which is pretty much what you’re saying. I was unable to find real analysis on that number, however, so just stuck with the more conservative number. All of that aside, you really only need one word to tell why electrical resistance heat is bad: coal.

  3. I agree with Tom on the fact the typically assume a site to source ratio of around 3, suggesting a 2/3 loss from primary energy to site energy.

  4. I may have missed it, but what will your heat source be?
    Have you seen the natural gas to electricity co-generation set ups?

    Very impressed with your plan, it looks great,
    Darcy

    • Darcy, I can’t speak for Paul but since I know that he and Des are spending all of their time getting ready for the electrical inspection, I may be able to answer. There will be hot water run through each floor in the house including the basement, and the water will be heated by an on-demand natural gas powered heater. The setup would allow them to use natural gas now but change the heat source some day down the road (ie solar) if / when it makes sense.

  5. There seems to be a little confusion about electrical losses, but you will be glad to know you are both right. The loss in delivering the electricity from the power plant to the house is about 7%. But those are just the transmission losses. Unfortunately we have not found a really efficient way to convert fuel into electricity. The best simple steam cycle plants convert about 40% of the fuel’s energy to electricity. Big diesels sometimes do as well, but usually not. Relatively rare plants that combine the steam cycle with a gas turbine generator can convert more than 55% of fuel to steam. The 40% is more typical, and then we lose 7% getting to our houses. So end-to-end efficiency is about 33%, and the other 60% must be dissipated to condense the steam so the water can be recycled. That heat goes into the air or a river. We could do a lot better if our power plants were near our homes, and the waste heat could be piped to our industries and homes. Then maybe 80% of the fuel’s energy could be used. But, unlike Europe, in the US no-one want to have a power plant for a neighbor, even if the cost of the heat was quite low.

    • Thanks for the clarification Gene. Those numbers, while disappointing, are hardly shocking.

Trackbacks/Pingbacks

  1. -28C and Just 2 Space Heaters! (Yes, I said Negative) | Clair's Bottom Line Blog - [...] I wish I could say that this is a wonderful new energy-efficient listing right here in Regina, but it’s…

Leave a Comment