Energy myth-busting: Is it cheaper to have heating on all day?

sue1201 wrote: »

Re electric heaters, my pet electrician says that only electric heaters are 100% efficient ie all the power used is converted to heat.

In terms of the power coming into your home maybe. But that electricity will have been generated in a power station that achieves nowhere near 100% efficiency, and is likely to have been generated from fossil fuels.

Bricks wrote: »

By the way. Just read the "Energy saving Myths" page on MSE. This may have been done already on the many previous pages of this thread, but the "ask jeff" article linked to seems very suspect to me

http://www.askjeff.co.uk/will-keeping-heating-increase-bills/

Firstly it seems heavily tinged with climate change denialism.

Secondly it makes a bizarre claim that those who advocate energy efficiency want people to be less comfortable in order to "punish" them for causing climate change!

Thirdly it contains a number of non-sequitur statements to do with condensation in walls, and nothing specific to back up its vague argument that this is relevant to the question the article claims to address.

I'd advise people to ignore this article. I also don't think it should be linked to on the MSE site because it seems to do nothing other than make a series of unsubstantiated claims.

Excellent post!

There is a recurring(and stupid) argument every year that goes along the lines:

'instead of heating my rooms to, say, 21C in the evenings, I find it cheaper to keep the thermostat 24/7 at, say, 16C.'

Whilst that may well be true, it ignores the fact that almost everyone finds 16C unacceptable in the evening.

Except those of course who post that 12C is comfortable!

My 2p.

The ask jeff article does make claims which are not backed up with studies. However, it is not an unreasonable argument. Wet bricks and wet cavity fill would be more conductive of heat than when dry and houses produce a lot of water vapour some of which escapes through the walls. My gut feeling is that water vapour isn't enough but that's just my gut I've no facts to back that up either way.

National trust did some tests in one of their properties and found their cost of heating was lower when it was on low 24/7. That could be because the walls stayed dry. Equally it could be because running low is more efficient that running high, especially on a condensing boiler where the difference is at least 10%. For dense property, which all National Trust places would be, the difference between 24/7 and broken running is a ~5% saving which hence would gave a saving on 24/7 running.

Turning off radiators in unused room is dubious IMO. The insulation in a house is in the outside walls. There is no insulation between rooms and of course air freely moves between rooms. Turning off a radiator in a room just reduces the radiator surface to heat the house. The unheated room is getting heat from the heated areas of the house. It has to be unless it is at outside temperature, i.e. middle of winter, -1C outside, -1C in unused bedroom, ice on the walls.... Doesn't happen. Turn the rad down by all means but keep it sensible, say 18 or 16C, warm enough to keep condensation at bay and so that there isn't too big a difference to the rest of the house. Otherwise that room will be sucking heat out of next door rooms since houses do not have insulation between rooms. The issue in reducing the rad area is that you make the remaining radiators work harder so hot so less efficient with a condensing boiler.

What most people fail to realise is that everyone is in fact heating their house 24/7. Take a house a 20C, outside is 0C. You turn the heating off at 10pm. Does the temperature drop to 0C? No (unless you live in a tent). What happens is that the house temperature slowly drops overnight to maybe 16C by morning. All through the night heat has been leaking out of the house. That comes from the structure of the house. The next morning when turn the heating on you put that lost heat back into the structure. The overall energy usage is similar, you save a bit overnight because the average temperature is 18C (20C->16C, avg 18C), rather than it being kept at 20C. The downside is that you have to make the heating work harder so it is less efficient.

I know people struggle with this let me give another analogy. You're in bed trying to keep warm. Option 1 turn on the electric blanket, call that 20W on continuously. Option 2 the house fairy brings you a hot water bottle, that took 6min of 2kW kettle to boil it. It lasts 10hrs. Option 1 uses 20W x 10hr = 200Wh. Option 2 uses 2000 x 6/60 = 200Wh. Exactly the same. Although option 2 only uses the power for a short time it is storing the energy. A house works the same way. You store heat in the structure and release it overnight when the heating off.

It is therefore not a given that running the heating shorter or turning off radiators will reduce you heating costs. After a point you are making the heating system work harder and so less efficient. After this point the heat saving is outweighed by the loss in efficiency so bottom line is less heat used but more ££ spent.