Heating an empty property

We have a mid-terraced house that's going to be stood empty for a few months. It's suffered a bit from dampness in the past so I think we should keep the heating on to some degree now that we're coming into the colder months, but what's the best way of doing it? An hour in the morning, an hour at night? Programmer/thermostat set to 'off' all day but rely on a minimum temp to switch it on if necessary? And if that's the best, what values for min/max (I think it's currently set for a min of 11C and a max of 12C). Or some other method entirely?
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Dave has brought this to us :

I would suggest setting the thermostat for 5C, to prevent pipes freezing and run continuously. If there is damp, I would consider installing a dehumidifier, with a built in humidistat and a permanent drain.
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On 10/24/2016 4:40 PM, Harry Bloomfield wrote:

Sounds good to me. You could leave the loft hatch open if there are any concerns about water in the loft. Perhaps turn off the water stop tap. Could perhaps go a couple of degrees cooler if you are confident about the thermostat. Sufficiently modern boilers tend to have their own frost protection.
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When we left my M-I-L's house empty while we sold it, the insurers wanted the loft hatch left open and the heating left on. Good luck with that. There wasn't any.
We also switched off the water and drained down the plumbing.
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On 24/10/2016 16:40, Harry Bloomfield wrote:

Most dehumidifiers come with a tube that can be fixed for a permanent drain, however as the house will not be used you could sit it next to the sink on the worksurface and just let the tube run in to the sink.
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On 10/24/2016 3:37 PM, Dave wrote:

Check what your insurance company requires - mine insists that heating be kept at no lower than 15C.
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snipped-for-privacy@lastname.oc.ku says...

Really?
What planet are they living on?
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On 10/24/2016 8:07 PM, Sam Plusnet wrote:

Really. I'm one of those people who reads all the fine print in contracts, and this requirement is fairly recent.
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On 24/10/2016 20:07, Sam Plusnet wrote:

You really do need to read the small print of the policy very carefully or you could find that when you make a claim they will not pay out if the property was unoccupied for more than some number of days. I have seen policies that specify 15C minimum or services all turned off and everything drained down. You pays your money and takes your choice.
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|||newspam|||@nezumi.demon.co.uk says...

I wasn't suggesting this misrepresented what insurers may demand, just that a minimum of 15C seems rediculous.

Trying to keep this house at or above 15C 24/7 throughout a winter would certainly involve a lot of "You pays your money".
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On Monday, 24 October 2016 15:37:28 UTC+1, Dave wrote:

With warm neighbours both sides you won't need heating unless it's in an exceptionally cold area.
NT
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On 24/10/2016 15:37, Dave wrote:

If it is unoccupied then the best strategy might well be to have the heating come on in the middle of the night to help counteract the coldest external temperatures around 4am and again in the early evening. During daytime the feeble sun will provide some input.

You could probably safely set the max to 9C and leave a couple of degrees above the frost stat which should be checked at 5C. I'm a bit nervous of going too low since it will be the very coldest spot(s) in the house that might freeze if you cut it too fine.
Your insurance policy may specify other limits whilst unoccupied or require a full drain down for winter.
You might want to check the pipe and tank insulation in the loft. Make sure there is no bare metal for drafts to play upon.
I saw the result of one of the severe winters on an unoccupied flat once - spectacular flood when the outer door failed. Not good!!
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On Mon, 24 Oct 2016 17:40:05 +0100, Martin Brown

Agreed. 9 or 10 deg is needed. 5 deg is no use for an internal frost stat.
The pipes that froze at a house I worked at few years ago were the pipes behind the kitchen cupboards that ran against an extarnal wal (no cavity wall)l. Leaving the kitchen cupboards open may have saved this from happening. Turning the stop tap off you have saved a lot of the damage.
Adam
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Dave expressed precisely :

Thanks folks. Just FYI, there are no tanks or pipes in the loft at all.
I like Martin Brown's idea of having the heating coming on during the night when it's coldest - seems so logical but I would never have thought of it :')
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On Monday, 24 October 2016 19:28:18 UTC+1, Dave wrote:

It isn't.
NT
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On 24/10/2016 19:28, Dave wrote:

The insurance policy for my holiday flat had used to have a clause requiring a temperature of at least 13C to be maintained when the flat was unoccupied during the winter months - otherwise there was no cover for frozen/burst pipes.
I figured that this was going to cost me a fortune in gas. My solution was thus:
I duly switched my progammable thermostat to frost stat mode set at 13C - but I wired it in series with an external stat set at about 2C. I couldn't see how it was going to freeze *inside* unless it was freezing *outside*. that meant that the heating maintained the internal temperature at 13C, as required - but *only* when there was a danger of freezing.
The insurance company has subsequently relaxed the rules, and now just requires the water to be turned off in order to limit the effect of any escape.
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I've had to do this with a few houses over the years, waiting for probate, and in my case back when I worked for a company which liked to send me away for weeks at a time in the early 2000's.
Leave the heating on all the time, but adjust the temperature setting appropriately.
Insurance may dictate a minimum temperature, below which you are not covered for burst pipes or consequential damage.
Otherwise, it depends on the house. A modern house will probably cope with running at something like 8C, which should stop corners dropping below freezing. For an older house, you may need to keep it warmer to keep damp out - I had to go up to 12C to stop it smelling damp. Note that ths stat is probably in the middle of a main room, but you need to prevent obscure corners with pipework going below freezing, so setting the stat too low will not provide protection where it's needed.
Some other comments:
If there are water pipes/tanks in the loft, leave the loft hatch open so some heat will get up there. If this is long term, might want to make up a ventilated grille to go in place of the hatch so bats, birds, etc can't come through.
If you have cupboards against outside walls with pipes in them, leave the cupboard doors open so the warmth gets in and they don't form a frozen cold spot.
Turn the water main off (preferably in the street), so that if there is a leak, the volume of water which leaks is limited to what's stored in the house. (This does raise an issue of what happens if all the water leaks out of the radiator circuit and the boiler tries to fire up - depends on the boiler.)
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On 24/10/2016 15:37, Dave wrote:

Check the insurers requirements, some may want it kept at 15 deg C minimum!
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Setting to 10 deg continuously isn't expensive and will guard against both frost and condensation damage. Leave cupboard doors and all internal doors open and prop the loft hatch open a few inches.
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On 24/10/2016 22:46, Peter Parry wrote:

Last winter I left a property at 7 deg for 3 months and it did suffer a bit from damp. This winter I plan to use a higher temperature. There are pipes but no tanks in the attic. The property is in an area where it is unlikely to freeze. The insurance does specify 15 deg but with the water turned off my hope is that any damage would not be to much.
At another property which has tanks in the attic and is in an area where it freezes, I have a thermostat in the attic set to about 1 deg. When we go away for a couple of weeks I leave the attic door open and rely on this frost stat. I have found that on cold nights this stat will trigger even when the property is being lived in with the heating on.
I have remote control of both heating systems and can monitor temperatures via the Internet.
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