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

Cardew

I have an old detached converted 2 storey outbuilding without cavity walls and I live in one of the colder parts of England. It is little used in winter.

I monitor the temperature constantly during cold weather and know the coldest parts of the building.

Last winter I never needed to heat the building(gas CH with combi) and the lowest temperature was 2C but usually around 5C.

In the very cold winter of two years ago I had the frost stat set to 5C and was surprised how little gas was used.

macman

It's usually draughts that cause loft pipes to freeze in cold weather. Lag all the exposed pipes, block up draughts, leave the loft hatch open if necessary, and the risk is minimised.

orrery

macman wrote: »

It's usually draughts that cause loft pipes to freeze in cold weather. Lag all the exposed pipes, block up draughts, leave the loft hatch open if necessary, and the risk is minimised.

The pipes are lagged to the extreme - foam tubes over-wrapped with felt lagging. The loft is ventilated to prevent condensation. The main problem is that the loft is well insulated and then floored, so little heat escapes into the loft - which is fine when the house is heated normally, but obviously not sufficient to guarantee the pipes don't freeze if the main areas are held on a frost-stat.

I deliberately didn't floor under the cold water tank, or add extra lagging because I recognised a potential problem if I did so

malc_b

DragonQ wrote: »

I'm afraid the science and evidence disagrees with you. It is cheaper to turn off the heating if you're not using it, simple as that. Partly because using energy when you don't need it is obviously wasteful, partly because boilers are more efficient when on full power, partly because heating the house by a degree isn't any harder when it's cold than when it's hot.

You're incorrect. Boilers are not more efficient when on full power. Max heat output requires very hot radiators so the condensing boiler no longer operates in condensing mode and less efficient. Or look at it another way. Burn some fuel to get hot gases, suck the heat from these gases to heat the radiator water. You get more heat out of the gases if the water is cooler so it is less efficient to heat radiators very hot, especially for condensing boilers. You might be thinking about short cycling when the boiler runs for short times rather than one big burn. Short cycling is inefficient but that can be cured with better controls and most gas boilers are variable these days.

Also, there is a suggestion that a cold house will have a lower insulation value due to have damp walls. In which case it would take more energy to heat a cold house than a hot house.

malc_b

macman wrote: »

It's usually draughts that cause loft pipes to freeze in cold weather. Lag all the exposed pipes, block up draughts, leave the loft hatch open if necessary, and the risk is minimised.

Most lofts are ventilated to stop damp problems. The more insulation the more ventilation they need. Opening the loft door would let in loads of damp air as well wasting a load of heat. Insulate pipes yes, and where possible insulate over the pipe but not under it so it can gain heat through the ceiling plaster.

meg75

I don't think leaving a window open is a good idea as it will suck the heat out.

The best way to dry clothes is with a dehumidifier.
Just park it next to the airer with it blowing slightly at it. The warm air it generates along with the extracting of humidity will have the clothes dry overnight, giving you time to stick another load on the airer before you head off to work. Uses barely any electricity and saves having that damp smell in the air and cold clothes that still feel damp even though they're dry.

orrery

meg75 wrote: »

I don't think leaving a window open is a good idea as it will suck the heat out.

The best way to dry clothes is with a dehumidifier.
Just park it next to the airer with it blowing slightly at it. The warm air it generates along with the extracting of humidity will have the clothes dry overnight, giving you time to stick another load on the airer before you head off to work. Uses barely any electricity and saves having that damp smell in the air and cold clothes that still feel damp even though they're dry.

... and a desk fan helps too. It seems to use about the same electricity as using the tumble drier to dry the same amount (lower power for longer).

scrapingbuy

Get rid of the central heating and get wall mounted gas fires. On for an hour before bed when temps drop below 17c. 4 bodies and a few candles does us until Oct/Nov in the main room. Cook every night in kitchen so no need to heat that either.

John_Pierpoint

malc_b wrote: »

You're incorrect. Boilers are not more efficient when on full power. Max heat output requires very hot radiators so the condensing boiler no longer operates in condensing mode and less efficient. Or look at it another way. Burn some fuel to get hot gases, suck the heat from these gases to heat the radiator water. You get more heat out of the gases if the water is cooler so it is less efficient to heat radiators very hot, especially for condensing boilers. You might be thinking about short cycling when the boiler runs for short times rather than one big burn. Short cycling is inefficient but that can be cured with better controls and most gas boilers are variable these days.

Also, there is a suggestion that a cold house will have a lower insulation value due to have damp walls. In which case it would take more energy to heat a cold house than a hot house.

What you are really saying is that simple thermodynamics requires the smallest manageable difference between the internal temperature (say 19 degrees) and the temperature of the heat source required to keep that temperature.

You then find yourself with convection from underfloor heating, and that has an element of night storage about it. Though there have been some advocates of vertical underfloor heating producing convection plus radiation from the walls and a faster response.

However we are supposed to be on the road zero carbon, where the house more or less heats itself and stays warm 24/7.

However the 80% of us who will live out our lives in houses already built, can continue to devate this ussue in the knowledge that all homes are different and an investment in insulation is probably 10 times more effective than marginal fiddling with the on/off clock and the difference vetween that and the "set back".

If you are still living in a Nissen Hut then a radiant gas fire is probably your best bet at staying healthy in a small snug room, coupled with a heated blanket for the bedroom if the external temperature is above freeing.

You won't be comfortable but you might manage to remain healthy provided you realise the threat of respiratory illness when the damp rises and the temperature falls.

anon_ymous

Herongull wrote: »

But surely it is obvious that this is nonsense! Makes you wonder about heating engineers.

Of course you are wasting money (and energy) if you have the heating on while you are away for the simple reason that whenever the house is warmer than the outside, heat is lost to the outside, and the rate of loss is proportional to the temperature difference.

So heating the house while you are out = wasted money, and the warmer you have the house while you are out, the greater the wasted money. The longer you have the house heated, the greater the wasted money.

I can't even think where this silly myth came from - it doesn't even seem plausible.

A year late, but thanks for this. Last year I was living in a student house with three other people. They were all hell bent on saying "If you leave it at a constant x temp" it will be cheaper..

It was 3 vs 1... In this flat, fortunately the thermostat only goes up when needed (Otherwise it goes right down), aside from now, because Im ill