Insulation under cold tank

[Theo]

What does the team reckon about this:

I know the conventional wisdom is to leave a patch of ceiling uninsulated under your cold water tank, but the tank is 3 foot in the air! There's completely free airflow from the patch of ceiling under the tank to the cold loft. The site is quite windy so convected heat is unlikely to make it to the tank.

It appears to have had 1-2cm polystyrene attached to the outside (not sure if also to the bottom, I forgot to look).

To allow me to insulate underneath while avoiding the risk of freezing the tank, I suppose the options are:

- add a better jacket to the tank

- add a heater on a frost stat inside the tank

- add a heater on a frost stat to the side/bottom of the tank

- something else?

Would tank lagging be sufficient for a tank in a cold loft, without additional heat flux from the house?

Thanks Theo

[Tim+]

Could you not box in the area under the tank? Then insulate the sides of the box (and tank) but leave the base uninsulated.

Tim

[newshound]

That's what I would do. You could even make the box from Celotex extending up the sides.

[JohnP]

That would be so easy to do and very neat.

[Theo]

Hmm... an interesting thought.

I hope to in future run some data cables underneath the tank parallel to the joists (since there's no insulation there at present), but maybe I could add a drainpipe to run the cables in before I celotex it all up...

Theo

[Harry Bloomfield, Esq.]

Theo submitted this idea :

It would only be OK, providing a cold spell wasn't too long, plus the mains flow into the tank was regular.

Insulating will help keep the heat in, but only for a while. I would suggest nailing carpet around the frame of the support stand and leaving the area over that ceiling uninsulated.

Another way, would be to add a source of heat to the tank. Can a cheap test tube type heater, with a built in stat, be set to operate at 5C?

[Theo]

I doubt carpet would help much, but celotex as suggested would.

That was my thought: don't waste heat for the 99% of the time it's not at risk of freezing - and also avoid transferring heat from the hot loft to the house on a summer's day.

There are things like this:

that's for motorhome (12V/8.5A) use. There doesn't seem to be an equivalent for domestic use that I can find.

I could drop an immersion in, but I can't find a suitable frost stat that will measure the temperature of the water (not the air temperature).

The only other kind I can find are fish tank heaters, which don't go cold enough. 'Pond ice heaters' may do but it's not clear they have thermostats, rather than things you just put in on cold days.

Theo

[Dave Liquorice]

I suppose the options are:

No.4 Insulate underneath and leave tank as is (I assume it's properly covered to keep evaporation in summer, in and wildlife, out)

Is the tank freezing going to be a problem? There is little to constrain the required expansion, it can just expand up the tank.

Our tanks are stood on boards about 18" above the ceiling joists. The Ceiling is insulated. Not noticed any problems in the "cold" loft. Remember mains water will still be above 10 C or so even in winter(*) and there will be some heat coming through the insulation.

We have had a couple of pipe bursts due to freezing. Same pipe, in the garage with no heat and only when its been down to -10 C ish for several days.

(*) PL footy grounds use this "warm" mains water to thaw the pitch surface on days when it's close to or just below freezing.

[Theo]

I think so, but I should check.

Why is there all this stuff about leaving under the tank uninsulated then? Or is the concern pipes freezing? (The pipes are all in clip-on lagging jackets, although not sure how effective those are).

I suppose the worst case is going away for Christmas when there turns out to be a cold snap - heating down low and no water drawn from the tank.

As it happens I have one of these (2ft 80W version):

I suppose I /could/ mount it inside the tank insulation somehow, controlled by a socket controller: others available)

Not entirely convinced that's a good idea (what if the thermostat jams on?) Feels like heaters next to foam insulation isn't a great plan, although maybe rockwool would be ok.

Theo

[John Walliker]

Self-regulating heating cable under pipe insulation should be OK, with a frost thermostat to activate it when temperature is just above freezing.

John

[Dave Liquorice]

Gawd knows, which is partly why I described the tanks here that have never had a problem even when it has been cold enough to burst a pipe in the unheated garage.

Pipe work is probably more of a problem but again no problem with insulated pipes freezing in our loft.

Heating down low, something that never happens here. Stone walls give the place massive thermal inertia, let it get cold and it takes days to warm back up.

[Theo]

I suppose I could wrap some trace heating cable around the tank, under some (rockwool) insulation. On a score of 1 to terrible, how bad an idea does this sound?

(is trace heating cable rated for being exposed to moisture?)

Theo