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.