lagging pipes: what to lag?

[Stephen]

Hello,

I am about to lift some floorboards and do some plumbing. I am unsure about whether to lag the pipes or not.

It seems to me that central heating pipes will be circulating hot water for hours each day, so it would make sense to lag these pipes, as heat radiated under the floor would be wasted heat.

I am less sure what to do with hot and cold water to the taps though.

I would think that hot water would only be used for short periods of time. By the time you switch a hot tap on for a second time, surely the pipes will have lost all of their heat whether they are lagged or not?

Would a hot water pipe lose much heat during the short time hot water was flowing through it to a tap? What if it were used for slightly longer to fill a bath or run a shower? Unlike the central heating, these pipes might only be carrying hot water for a few minutes each day. Would the cost of the heat loss exceed the cost of the lagging?

Is there any point lagging the cold water pipes? In my last house, condensation always formed on the pipe work where the main entered the house. I guess lagging that section would prevent condensation. Is condensation likely to form anywhere else?

Would lagging the cold water keep it cooler in the summer? I can't imagine that it gets hot enough under the floor to warm it up on a summer's day, and it would soon flush through with cold water from under the street.

Is it more that I should lag the water pipes to protect against freezing rather than heat loss?

Thanks, Stephen.

[Tim Watts]

It will keep the water hotter for longer in the pipe in the case of intermittent use of a tap (eg kitchen) - upto a point.

IME condensation is only a problem with mains cold pipes in kitchen and bathroom environments.

A bit.

Have had experience of an unoccupied house over winter (probate job), even with zero heating, pipes within the main house have virtually no chance of freezing. However, it is very worthwhile in a cold loft or garage.

There's another reason you missed - it's good to lag hot pipes near electrical cables.

But overall - if a hot pipe has space to lag, pop some in, there's no disadvantage.

[News]

In message , Stephen writes

Lagging pipes will not hurt, and will doubtless help. As regards freezing, so much depends upon where you are, house construction, weather, wind direction etc. Here (Aberdeenshire) in a Victorian granite house, we awoke one morning to find four radiators at the front of the house frozen solid together with the supply pipes under the wooden floor. That night had been unusually cold even for NE Scotland, with the wind blowing directly at the front of the house. The pipes are now deeply buried in loft insulation.

Of the four radiators that froze, the two upstairs did not split. Perhaps just enough heat generated by the bodies in the rooms? The two downstairs did split, but did not flood - we woke to find solid 'stalactites' of ice from the radiators to the floor.

[ARW]

Ouch!

When we had the minus 12 deg winters a few years ago I left my CH on 24/7.

A friend who had an empty house did the same but the incoming supply did freeze (stop c*ck and meter in a kitchen cupboard on external wall) and flooded the house.

[Tricky Dicky]

I would lag, in the eighties we went away at Christmas, weather was quite m ild and we left the heating off. It turned bitter a few days before we retu rned. Oddly enough it was a pipe running under the bath nowhere near a wall that froze and burst flooding the kitchen below. The water refroze so limi ting the flood but we returned to icicles hanging off the kitchen ceilings and one wall. Never again we always leave the heating on it costs less in f uel than repairing the damage from a burst even if you have insurance you n ever seem to get fully compensated for all your losses and inconvenience.

Richard

[Vir Campestris]

Heating pipes under the floor - most likely the heat will end up in the house anyway, so why bother. In the loft is another matter.

Our new thermostat BTW doesn't have an "off". If you really want the house to be able to get below 5 you have to turn off the system supply. Overnight off on the timeswitch gives you "not below 5", as does "I'm away for a fortnight".

Andy

[Steve Walker]

We have independent timer/stats for each room and if we go away in the winter we leave the living room on normal (for our cats) and turn everything else in the house to the frost setting, so nothing drops below 5°C.

[Andrew Gabriel]

Those under my ground floor are insulated with thick insulation to protect against freezing as it's outside the heated area of the house, and could in theory freeze. (No insulation will protect against freezing forever, but will delay the process, hopefully until the potential problem goes away.)

Pipes which are inside the heated area (such as between ground floor ceiling and first floor floor) are not insulated, since the heat they lose just adds to the upstairs heating with a bit of underfloor heating. They are sleeved with insulation where they run near cables, and should be sleeved near cold water pipes so as not to heat them. This can be thinner insulation than is used for frost protection.

I wouldn't worry about it (unless you have a hot water loop).

Yes, this can be a problem, particularly if the pipe is in a humid room such as kitchen or bathroom. If you are being a perfectionist, insulation to protect against condensation should be closed-cell insulation, as used on aircon pipework, otherwise it can eventually become waterlogged.

In different situations, freezing, heat loss, and condensation.

[Davey]

My neighbour went to stay with his son and family a few Christmases ago, and left the heating in his house at a sensible temperature. Some days in, his household medical alarm went off, the operator contacted the local friend who went to the house to see what was happening, and on looking through the window, he saw water running down the walls. In the loft, the fill ballcock for the cold water tank had frozen and split. There was much damage, and the operator who had taken the call reported that when he answered the automatic call, he had heard the sound of running water coming over the line.

So lag, lag, it may save you lots of money and hassle.

[News]

In message , ARW writes

Ouch indeed, but it did mean the split rads could be unbolted and dumped in the garden without worrying about dribbling dirty water through the house :-)

We now do that. The benefit of experience. All pipes and tank in loft are buried under mountains of insulation. OTT, but better than the alternative.

[Tim Watts]

Another wise move is to have an accessible and working stopcock and turn the mains off if away for more than a couple of days in the winter months. That reduces the vulnerability to the bit of pipe before the stopcock - and even in the tiny event that goes, the damage would hopefully be limited to one ground floor room.

[Sara Dawes]

Back in the 1970s when I installed our central heating the corrosion inhibitor (Fernox I think) that I added was also an anti freeze provided it was topped up each year. I assume that modern corrosion inhibitors are not specified as an anti freeze otherwise the pipe freezer kits that the same companies make wouldn't work.

Alan

[Martin Bonner]

"anti freeze" doesn't *stop* water freezing. It just lowers the temperature at which it does so. Modern corrosion inhibitors *will* have an anti-freeze effect, so the freezing kits will need to get down to -10 or -20.

[DerbyBorn]

Why would you want the house to go below 5 degrees?

When I go away, I leave mine on 15. Hate it when the insides of cupboards and wardrobes feel cold after being back home for several days.

[ARW]

Not so sure that would have worked in Graeme's case. It is possible that the pipes under the floor could freeze before the room stat at 5 deg decides to call for heat. The firing up of the boiler would then do nothing to help increase the room temperature on the other zones!

And I can beat Graeme's ouch:-) The owners of the house had gone away for a winters fortnight break and the night before they were due back the neighbours lit their solid fuel boiler for them. Every pipe was frozen and the boiler exploded knocking out a wall and setting fire to the house.

[News]

In message , ARW writes

It is the wind that is the killer here. Lowest temp we have seen is -15 to -17 but even that is not too bad without wind. When our pipes and rads froze, the cold wind was from the north. Downstairs, suspended wooden floor with grills facing the wind. The pipes didn't stand a chance, but are now very well insulated.

Major ouch :-) We have never been away during the winter since moving here, partly because of house and heating, but more because the weather is so unpredictable. We may be able to get away, but getting back could be a problem. We just don't bother. In the event of an emergency, and we had to go, I would turn all the stats down to 2, and leave the boiler running most or all of the day and night, and bugger the oil usage.