Frost protection design - terrace with basement boiler

[gball]

Morning,

This is more a thermal / heat loss question than wiring+plumbing (I can do the latter!)

I have a 3 story Victorian terrace house that will be left unoccupied over winter, but I will be leaving the boiler powered, and do not want to fully drain the CW system. The plumbing layout is fairly standard 70s design:
- vented HW (tank in bathroom)
- CW tank in loft (tiled pitch roof - assume moderately but not well insulated) Pre-dates Byelaw 30 - tank has no lid / insulation, pipework has standard expanded foam insulation
- gas boiler in basement. Boiler has no internal frost stat.
- S-plan plumbing (not really relevant, but I mention it just in case)

Last year I set the system up with a programmer that had a 5oC frost setting, programmer is on ground floor (i.e. low point of airspace) I'm concerned that's not enough

So my current thoughts are:
1. Add frost-stat to basement area. The basement is enclosed by the other houses, so I doubt this will click in.
2. Lag the tank. I don't think there's any reason not to.

Here's where's it gets more tricky:
3. Potentially add 'third' frost-stat to top floor of house. (Second one being the one that's on my ground floor programmer already) That's the first question - in my mind the top should always be warmer due to thermal currents. Is that frost-stat a waste of time?
or 4. Put the third frost-stat in the HW cylinder cupboard - the pipework is all exposed there.
or 5. Put heating tape around the pipework in loft space, and put a frost-stat to switch that? (I bet it will run for days as the heating tape won't warm up enough to affect the stat temperature)

Sorry - have realised that's a very long post (almost a night in the pub conversation)!

I think it boils down to whether I believe the loft will go below freezing while the house is 5oC. I have no idea... is it overkill to use heating tape if I already maintain a minimum 5oC temperature? Does covering my house in frost stats work any better than just having one on the ground floor? Any experiences gratefully received!

 

[D_Hailsham]

Have you checked your Buildings Insurance Policy? It may insist that you drain down if you are away for a long time, or you won't be covered.

 

[gball]

Actually, I'm only going to be away for several days - but I'd assume even 72 hours is enough for the house fabric to drop to outside temperatures.

[edit - basically out over Christmas week, and then another week and a bit around then, without telling the world that the house is ready for burgling ) ]

 

[D_Hailsham]

Actually, I'm only going to be away for a few days - but I'd assume even 72 hours is enough for the house fabric to drop to outside temperatures.

You did say:

I have a 3 story Victorian terrace house that will be left unoccupied over winter

So I assumed it would be for several weeks/months.

The cellar is unlikely to drop much below 10C - don't forget the cold water pipe coming into the house doesn't freeze up as the ground temperature is fairly constant.

The loft is the problem area as it is outside the insulated envelope - assuming insulation between the joists.

Are we talking water pipes or heating pipes?
If they are already properly insulated there should be no need for a frost stat or heating tape.

If you want to protect the heating system, you need a frost stat and a pipe stat. The frost stat turn the boiler ON when the temperature drops below, say 5C, and the pipe stat turn it off when the water temperature reaches, say 20C. This prevents the boiler running all the time.

 

[Agile]

If you dont give us the correct details then we cannot give you the best answers!

For a short time away just leave the CH on 24 hrs at a low room stat temp and I would suggest 10 C.

Idiots leave it on timer without realising a house can cool down a lot in two hours when its freezing outside!

Tony

 

[JohnD]

pipes in a loft will freeze quickly, tanks won't. I have experienced it twice. You presumably have lots of loft insulation to prevent heat from the house leaking into the loft.

If the roof is unfelted, the loft will be very cold especially at night.

Pipe lagging will slow down the rate of heat loss, but not prevent it, and when you are away there will be no water flowing through the loft pipes so it will just get colder and colder..

If the water supply is not turned off, the pipes in the loft to and from the tank may burst, and water will gush out until you turn it off.

I strongly recommend that you turn off the house stopcock. If you turn on the cold tap in the kitchen, water will tend to dribble down from the pipes going to the loft, especially if you run the hot tap enough for the CWS ballcock to open.

If you refuse to drain the tank, the amount of water damage to your house and possessions will be limited to the contents of the cold tank.

 

[gball]

Thanks. I will be turning off stopcock, but want to avoid draining system each time.

I'm actually after a more general solution to set up for the next few years, the house is left empty for weeks at a time - and I'd rather have something self-protecting, rather than relying on the person who leaves last to carry out a specific action (hence permenantly installing the frost stats)

I think I will go for heating tape in loft for the CW mains. Would that be needed for the CH circuit given the water is treated, or does inhibitor not really lower the freezing point?

 

[JohnD]

the CH pipes in the loft, apart from getting very cold, may have quite fresh water in them if the system has been topped-up from the F&E. There is a slow mixing of water in the F&E with that in the radiators as it expands and contracts, but this is very slow. You can add an antifreeze to the system, preferably one by th same maker as your corrosion inhibitor so they will be compatible. It is not very cheap.

You might be intererested to know that I had a burst in the feed pipe to an F&E, because there was no topping up, the water in this pipe did not flow at all during the winter, so it had a matter of weeks to cool, and froze one frosty night, even though the house was maintained at 12C while I was away.

Taping all the pipes, and having a frost stat in the loft, is probably the best solution, and does not depend on user intervention. Insulate the pipes over the tape. Pay special attention to elbows and bends where the insulation may gape. The BS grade of Climaflex or similar is best, it is as thick as your arm. If you are able to flop the loft insulation over the pipes, it will help include them in the warmth of the pipes.

It is a great advantage to turn off the stop cock when the house is unoccupied, you might like to add an extra (full bore) valve where it is easily accessible. Turning on the tap to drain the tank will give even more protection.