Underfloor Heat mat as a background cold water tank heater

[akgray]

Hi All,

We have a house high up in the Pennines and it can get very cold in the winter, for prolonged periods. The last 2 winters have seen me up in the loft with a hairdryer/hot water to unfreeze the pipes and tank, as you can imagine its a bit of a pain.

What I would like to do is install an electric heat mat, the type for underfloor installs around the tank and box it in with kingspan to make a low level, heated and insulated box which should not freeze.

What I want to know is, would the under floor heating mat need to be attached to boards and a screed applied to act as a heat sink for the heater, or can it be attached to boards and run bare?

Any help appreciated, Thanks.

Andy

 

[ChrisRogers]

One of the properties I manage isn't heated, we use the following solution:

All pipes are protected by trace heating
Water tanks have immersion heaters fitted - controlled by a frost stat and contactor. The system works brilliantly.

 

[akgray]

Thanks Chris,

Could do but I have some of this stuff already from another job. I may replace the copper with plastic anyway which should sort the issue up to the ballcock but the last 2 winters have seen an inch of ice on the top of the tank too.

Have you got any links to the stuff you have used?

Cheers

Andy

 

[PrenticeBoyofDerry]

Your tank and pipes within the loft space need insulating correctly and also ventilation below the tank pedestal. If you start using heat mats etc you may introduce bacteria to the stored water, which can then become harmful, as it must be kept below regulated temperatures to comply with water regulations.
Insulating tank and pipes will prevent both freezing and over warming, if the pipes still freeze you may then consider heat tracing the pipework, which can help maintain temperatures.

 

[ericmark]

There are two basic types of trace heating and both are also used for under floor heating. The Basic type is a lenght of cable with a resistance wire in it normally linked at the neck area so it can be cut to lenght. This type can over heat to silly temperatures.

The other type uses a chemical (RAYCHEM for example) and as the cable gets warm so it's resistance increases so it is reasonable self regulating.

With the cheap type with a simple resistance wire you do need something to absorb excess heat. With the latter type it is not so important.

We had issues with some makes of trace heating as it could make the pipes become live as there was no earth screen we found the fitters during maintenance would disconnect pipes without linking earths and it was these very people who would get a shock as a result.

This resulted in old being ripped out and being replaced with new that did have an earth screen.

There is some which can't be cut. And even that which can there are special ways according to make to protect the ends.

I would not consider it as a DIY job.

 

[akgray]

Thanks for the replies.

Prenticeboyofderry, The loft is well insulated but it is a second home and often left without heating for a while. The house is a couple of hunderd years old and in the bottom of a valley so sometimes it stays cold for ages (the Christmas before last we had 10 consecutive days where the max temp was -6C. There is ventilation below the tank, I hadn't thought about the bacteria level and its a good point but during the summer it is regularly +10C for months, I was only looking to keep the temp at 5C or so so not sure if it would be a problem, the kingspan box would need to be vented which I hadn't thought of.

ericmark the underfloor heating I have can not be cut so it may be the raytherm type, I may just wire it up and see what happens to the temp as I monitor it, you have given me another idea, why not unravel the underfloor heating wire and use it as a trace heat? Would need to monitor it but it would be a lot easier install, not sure how the controller for the underfloor heating would cope though.

Thanks again for all the help, its a great site this

 

[ban-all-sheds]

The loft is well insulated but it is a second home and often left without heating for a while.

That's one basic flaw you need to fix - the CH should be running on a setting where it doesn't let the house drop below a certain temp. 6° rings a bell.

Not that that will help the loft temperature - if the insulation is working then it should be cold up there even when it's toasty downstairs.

Seems daft to heat an uninsulated space - better to enclose the tank and pipes and make them part of the conditioned space.

Or install a combi and move away from the idea of keeping water in the loft.

Or if it's going to be empty and cold for periods during winter, why not drain the tank and pipework down when you leave?

 

[akgray]

Hi ban-all-sheds, thanks for the reply.

There is no central heating or mains gas. We have tried heating the downstairs by leaving on storage heaters but as the loft is well insulated and the roof is not, the loft space still gets cold. The storage heaters cost a fortune to run (about £10 per week per heater) even on Economy 7 and there is no easy way of controlling them to switch on when the temp drops as there is no phone line either.
I have started draining the supply pipe to the tank by turning off the water and running the hot tap for a while, I was just thinking about other ways to overcome the problem as it would take a long time to drain the tank each time we left.

 

[ban-all-sheds]

Aren't there any cold taps fed by the tank?

Toilet cisterns?

 

[maltaron]

It is unwise to leave open tanks full for any length of time, theat is asking for bacterial infestation. As it appears that the loft piping is the maind problem why not put a 28mm plastic pipe with a valve to outside. That will empty the header tank in no time.

 

[akgray]

Hi both

True I could empty the tank faster but I was hoping to avoid it. The tank is covered in the loft but you are correct malatron its the loft piping that's the main problem. The drain is a good idea but the walls are stone and 2' thick. It would probably be easier to use the main drain at ground level and put a pipe out the window

Still would like to hear if anyone has ever used the underfloor heating element as a trace heater before I try it anyway. I will let you know how it goes.

Cheers

Andy

 

[Robin0577]

As others have said, make sure the insulation is right first, but if you have to go down the heating route, how about something like this?

http://www.bradshawsdirect.co.uk/pond/pond-accessories/pond-heaters/bermuda-pond-heater-150-watt

Quick, easy and fairly cheap

 

[AndyPRK]

check the pipe route to ensure it's not near the roof edge/eves.

wrap loads and loads of insulation around a group of pipes.

 

[bernardgreen]

Beware of making the water in the tank too warm. Apparently it is now considered a serious health risk, bacteria breed rapidly in warm tap water

It is true that storage tanks are a breeding ground for bacteria and they breed faster in warm water than in cold water. So set the thermostats as close to freezing point as possible.

Building regulations seem to object to a domestic storage tank being heated by "waste" heat from an air conditioning system as it becomes a breeding ground for legionella . In a commercial property it is acceptable to pre warm a tank of water before it goes to the hot water system as the professionally maintained hot water system will ensure that before use the water is heated to a temperature that will kill the bacteria.

 

[bernardgreen]

I was just thinking about other ways to overcome the problem as it would take a long time to drain the tank each time we left.

You might be OK leaving the tank full and draining the pipes. A gate valve on the pipes leaving the tank and vent valve to allow air into the pipe as the water run out at a tap. ( or just a pipe "T" ed off and it's open end higher than the tank with a mesh cover to prevent thing getting into the pipe )

The tank can be protected from damage by expanding ice by empty plastic bottles half submerged. In theory these crush under the pressure of the ice as it forms and save the tank. It works in rain water butts, I haven't tried it in tanks in a loft.