Winter is upon us, and all across the southern states people are reviewing their energy bills and thinking about how to make them smaller. Recently many people have asked what is the most efficient way to heat their homes.
As with anything to do with thermodynamics, the answer is complicated, but there are some solid rules to help shape your thinking.
Simply put, insulate, insulate, insulate, then add more insulation.
Both heating and cooling come down to one fundamental problem; how to put heat where you want it and keep it there. That means outside in summer and inside in winter.
The rate that heat enters or leaves a building is governed by the materials that make up your “building envelope:” the surface which surrounds your living spaces. You have to prevent heat from crossing the boundary of your walls, ceiling, floor, windows, and doors without your permission.
We say “without your permission” because in winter your first priority must be getting sunlight into the house and keeping it from leaving again.
Direct sunlight is almost entirely ultraviolet (UV) radiation, which passes easily through glass and into your living room. Once it strikes an object, it heats up and the sunlight becomes infrared (IR) radiation, which is best thought of as radiant heat. IR radiation doesn’t pass through glass as readily as UV radiation, so the room heats up. Ever left your car in the sun for a day where it is a lovely 70 degrees outside but 113 degrees inside your car? It is exactly this mechanism at work.
An air source heat pump must meet or exceed 15 SEER and 12.5 EER and 8.5 HSPF in order to qualify for the tax credit. Package heat pump systems must meet or exceed 14 SEER and 12 SEER and 8 HSPF.
Insulation will prevent heat from crossing boundaries. If you own your house, the path is well trodden and fairly simple. Start with the ceiling, adding the thickest insulation you can find. The lack of attic insulation is the second largest contributor to higher utility cost only to be outpaced by a poor duct system and inefficient heating and cooling equipment. Attic insulation should be at least an R30. The “R” rating is the insulation’s ability to resist heat transfer in the summer and winter months. The larger the number the greater its ability to reduce the heat transfer and reduce your energy bills.
Next, consider how the wall insulation can be improved. There are some new materials and processes available for this task, and you can pay someone to come and pump insulation into your wall cavity for $2,000 and upwards. Doing this can make your house about 2 degrees warmer.
Window treatments are just about on par with walls for making a difference; even more so if you include doors.
If you’re on a budget or renting, there’s a lot you can do with windows and doors. First, seal all the gaps around doors in the house, even the internal ones, to control the size of your heated space. There are rubber seals that can do the job for doors and windows.
Then seal all the ancillaries that let heat escape, like bathroom vents and the rangehood, which vents outside. This is where renters can get creative and reap rewards; rolled towels under doors are a good start, but why not go further? Tape a garbage bag over the window that opens onto the neighbor’s bathroom. Block the old chimney with anything you can find. Do anything you can (safely) to keep heat from going where you don’t want it to go.
Curtains and pelmets are virtually mandatory in cold climates. Curtains must be as heavy as possible, touching the ground and the walls next to the window. Windows are the last great frontier in home insulation, and honestly, there’s no cost-effective way to retrofit them. Energy payback on double-glazing your windows could be close to 70 years. But as with all energy efficiency upgrades, there is more to it than the energy savings. What is niceness worth to you? How much nicer is it being in a house which is 73 degrees instead of 70? What is that worth to you?
Once your windows are done, think about what you can do to the floor. Slabs are hard to change, but there are products for suspended boards which will make a big difference.
You then have three choices for heating: electricity, gas, and wood.
The cost of wood is variable and will likely increase in the coming years. The environmental impacts are strongly dependent on your fuel source. Fallen timber is not fair game. It is a vital habitat for some animals, so it should not be burnt. Particulate emissions are a concern as well.
Gas is great in that it can deliver astonishing amounts of heat quickly, with lower greenhouse gas emissions than grid electricity, but not as low as renewable energy. Plus, future costs are quite uncertain. Gas heating is traditionally considered to be pretty cheap. But gas prices are tipped by many analysts to climb steeply in the next few years, much as electricity has in the last few years.
That leaves electricity as the only option which can have zero emissions. Switching your electricity supply to Green Power, an accredited and audited scheme which supplies 100% renewable power, means zero emissions electricity any time you want it. But how you use it is very important, as not all electric heaters are created equal.
There are two distinct classes of electric heater; plug-in heaters, and heat-pumps (or reverse cycle air conditioners).
All of the plug-in heaters end up at the same efficiency. They convert electricity into heat, the most basic form of energy, and will only ever produce a maximum of 2.4kW. It doesn’t matter how it does its radiant bars. A hot wire and a fan or a clicking oil-heater- 2.4kW of electricity becomes 2.4kW of heat and not a drop more. Buy the cheapest one you can.