What temperature to set on heating for unoccupied house

[ey143]

I have set my thermostat at 6.5 degrees for an unoccupied house during the winter to prevent freezing of the pipes. Is this sufficient? It's fairly large and the bills are usually expensive so want to only burn as little as needed to keep the house in safe conditions whilst we renovate.

 

[mfarrow]

I think during the big freeze of 2010 the insurance companies were specifying 10.

To be honest there's not a lot of chance of getting below that in 'normal' weather due to ground heat and good insulation these days.

 

[JohnD]

my insurers specify 12C, 24 hours a day, when unoccupied, and that you should spend at least one night a month in the house, or cover will lapse. If you have a look at your policy it may say something similar. The fuel cost is quite low, because most of the time the outdoor temperature will not be much less, and you will hopefully get some solar gain on sunny days, even if cold.

It is wise to turn off the water stopcock, and drain any loft tanks using the bathroom taps, because any pipes in the loft will be especially cold, even if lagged, with no movement of water when the house is empty.

This winter has been unusually mild, at least down here.

 

[TCCHeating]

Most insurers specify 15 degrees. It may seem excessive, but you would be devastated if anything happened and the insurance wouldn't pay due to smallprint. But as previously said. Check your policy

Merry xmas

 

[ey143]

I recently changed insurer and declared the house as a second home and being unoccupied and yes I think the stipulation was that we stay there once every so often and that the temperature was set to 15 degrees. Sod that cos my place is always cold and will cost a lot to maintain that temperature it's not realistic in my opinion. How do they check that anyway because the utility bills won't necessarily reflect someone living there given the low energy consumption.

 

[JohnD]

You might as well not have asked.

Is this sufficient?

 

[TCCHeating]

How do they check that anyway because the utility bills won't necessarily reflect someone living there given the low energy consumption.

They would know. They're not stupid! There is a big difference between 6.5 and 15 degrees. If a pipe burst in the loft they would calculate the heat loss of the house into the loft using the ratio of 15 degrees indoor temp and whatever the outdoor temp was at the time. They would be able to calculate the temperature in the loft within a few degrees accuracy. You could prob get away with 10 degrees, but 6.5 is just asking to void any insurance claim.

 

[Ltnman]

Not all houses have pipes in the loft. In that situation 6.5C would be fine for the house.

 

[ey143]

Please tell me if my logic is flawed.

I have now increase the temp on three thermostats to 11 degrees (my house has sectional heating and control valves etc so I can heat upstairs independently from downstairs).

Am I wrong in thinking that if I set it at say 15 degrees, the "heavy" cost implication is only a one time effort to get the room from a current temp of 7 degrees to 15 degrees (maybe a full day or so). But after that the incremental cost or burn is to keep at at 15 therefore it shouldn't cost a lot because the existing heat might marginally fall below the 15 threshold.

Hope that makes sense what I'm asking. Basically as long as the heating never falls below 15, it is a one time cost to get to 15 or another words it's more economical to leave it on constant rather than let come on a timed event?

 

[JohnD]

you are wrong

heat loss (and therefore heat input required to maintain temperature) is directly proportional to temperature difference x time

So if the external temp is 5C, and you heat your house to 10C, you are maintaining a temperature difference of 5C which costs you £x

If the external temp is 5C, and you heat your house to 15C, you are maintaining a temperature difference of 10C (twice as much) which will cost you £2x (twice as much)

How much £x is will depend on the size of your home, how well insulated and draughtproofed it is.

...more economical to leave it on constant rather than let come on a timed event?

this is a popular, but wrong, belief, because heat loss is also directly proportional to time. To keep a kettle boiling for 24 hours will use twice as much energy as boiling it for 12 hours.

 

[mfarrow]

There are obviously arguments to be made though that the house will take a long time to heat from cold and therefore you may need to run your boiler at a higher temperature, loosing some efficiency.

But it's immeasurably less that the heat lost due to temperature differential as discussed above.

 

[ey143]

Yes you are correct and I kind of knew this already in a roundabout way but was assuming decent insulation so there wasn't a huge drop in temperature which would then contradict a low temp rise from 5 to 15. Perhaps the reason I asked the question is when I relate it to one of those hot water taps that you can buy. The salesman says once the water has reached 85°C it is only a marginal cost to keep it at that temperature going forward.

 

[JohnD]

The "decent insulation" and the "marginal cost" are what determines the size of your £x.

The cost will still be £2x if the temperature difference is twice as high or if the time is twice as long.