Something you can do this year?
I'm really pleased to offer you the third and last (for now) guest post from Mark Brierley today (you can see his first one on low-energy here and the second on building a low-energy house here). Mark is a certified Passivhaus consultant and blogger, and he is generously sharing his knowledge and experience with us today. You can read more of his writing at his excellent blog, or get in touch with him via the blog's contact form.
"If you have an older house then your options are more limited than in a new build, and it will be much more difficult to reach a high standard of energy efficiency. But heat does not care whether you are in a super-insulated house or a drafty barn, it will still find the easiest way out. As you come up with a strategy for home improvements, your priorities for insulating depend on two questions: where are you losing the most heat? How much will it cost to add insulation there?
The aluminium window frame is perhaps the single worst thing that has happened to Japanese architecture, and if you have any in your house, that is probably the biggest heat loss. In general, houses lose at least 30% of their heat through the windows, and more than 40% of heat comes in through the windows in the summer. Not only is aluminium around 2000 times better at transferring heat than wood or PVC, your windows may also be leaking air. Even if your walls have no insulation, the wood, plasterboard, siding and air gaps between will insulate better than many windows, so your easiest way to improve energy ratings is probably to change your windows, or add an extra set of windows. As Ben has written before, contractors will often encourage you to use the cheapest products, with the intention of saving you money. Often, in the long term there is nothing more expensive than buying the cheapest option. Having said that, you can make a difference with low-cost, temporary measures, like putting bubble wrap or plastic panels over the windows and frames in winter, or hanging curtains across the entrance door (-RetireJapan: "we did this for years -makes a real difference").
Window performance improves with a wider air gap in the double glazing since air, not the glass, is an insulator. The U value, which measures performance and will be displayed on any good windows, goes down with PVC or wooden frames, low-E coatings, argon or krypton fill, warm-edge technology, an insulation layer within the frames, and triple glazing. As the U value goes down, the price of the windows goes up, so you can calculate how much heat your windows will save, if you know the annual heating demand in degree hours. There will be diminishing returns from higher performance windows since the heat finding its way out through your walls, roof and floor will become more significant.
Loft insulation may be relatively easy and cheap to install, and will make a difference in the winter since heat rises. It may also make a difference in the summer when heat comes in from the sun-baked roof. Walls and floors presents a much bigger challenge, and you need a clear strategy since bits of insulation do not work in isolation. Improving your windows will probably mean a bigger proportion of heat is lost through your roof. Adding insulation there will mean the heat escapes through the walls. Insulate those and it will escape through the floor. Insulate there and heat will find weak links in the walls, roof and floor, and the joints and corners between them. If you can insulate everywhere then your biggest heat loss may be in air leaking in or out, so you need to make the whole house airtight. And if you can make the house airtight you are going to need to put in a ventilation system. At every stage there is a danger of creating cold surfaces or cold spots, which will lead to condensation and the risk of mold and structural damage. Only two kinds of house can be guaranteed to have no condensation: a drafty uninsulated house, or an airtight, highly insulated house with ventilation.
There are many home improvements you can make that will affect your energy usage, but they may not affect it how you hope.
For example, underfloor heating can improve comfort, but there are many pitfalls. If there is not enough insulation underneath the heating, then you will be heating the ground rather than your room. Similarly, heat will find its way into the next room if it is not installed carefully. Hot water or coolants from heat pumps are cheaper and more effective at providing heat than electrical elements, although hot water systems may cost more up-front. I’ve heard stories of people who have put in electrical underfloor heating, used it for one year, then seen their electricity bills and never used it again!
If you are living in a poorly-insulated Japanese house with no central heating system, then the low-energy heating options are probably kotatsu and fan heaters. The kotatsu table heater has the advantage of heating up a small area, and the fan heater can be moved to where you want heat, so their low-energy credentials lie in their scope rather than their efficiency. Air conditioners are rapidly becoming one-stop wonder devices for meeting all your cooling and heating needs, and like refrigerators they are steadily becoming more efficient, typically doubling in efficiency every fifteen years.
Solar panels are another obvious addition you can make to a house, but I don’t think these should be seen as a low-energy investment. The first priority should be to reduce the amount of energy you use, rather than generating more energy. Adding solar panels is probably a good idea, but I think that needs another series of posts!"
Mark's blog, mostly about low energy building in Japan
Thanks again Mark! I really enjoyed the low-energy series and learned a lot. Will be putting it to use when we build our house in 3-4 years time :)
Any other tips to reduce energy use without major home upgrades? Any questions for Mark? Please ask in the comments or head over to Mark's blog.