Any disadvantage in using 22mm instead of 15mm copper pipe?

If you change to unvented or combi, 22mm pipe has greater volume of water to be run off before the hot arrives at the tap.

Owain

Any reason not to install a pump at the base of the tank?

Mine has its own 22mm cold feed from the header tank, and a techflange giving it a dedicated 22mm feed from near the top of the hot tank, these stay in 22m on the output side of the pump until they reach back up to the loft, then reduce to 15mm for the trip across to the bathroom and down.

Other than cost, the only other point is that for hot water at least, you increase the amount of water you need to run off before the hot gets to the point of use.

I doubt you would notice any difference at the shower head unless you increase the pressure by: raising the header tank, converting to mains pressure or adding a pump. However, it *might* be beneficial to provide the showers with 15mm dedicated feeds from a 22mm feed from the tank.

Is that not the same when using a header tank he already has?

Yes, but

- the problem is less acute with a tank than with a combi which fires up every time

- with a header tank the larger pipe may be needed to get a useful flow. With a mains pressure system flow will be adequate through a smaller pipe.

Owain

It wasn't uncommon to run 3/4" (pre-historic version of 22mm) for both hot and cold from the tanks to quite close to the points of use.

IIRC our bath might have had 3/4" right to the taps (bath taps are usually 3/4" threads rather than 1/2" more common on basins)

The only disadvantage is that you have to shift more water to run the hot though - though with a tank, you can add a circulation device which primes the pipe - rare but exists in places where the owner is big on not wasting water.

I have an Aqualisa shower designed for 22mm feeds. From a low pressure header tank system. Brilliant shower - high flow low pressure. Same with the feeds to the bath. No point in 22mm to a basin etc though. As the taps themselves will throttle the flow.

I think that the overall pipe 'resistance' is lower even with some sections of 15mm left in... so do what you said.

True that too...

No too bad if you lag the circulation loop well, and have a timer on the pump to limit its operation to "likely" times of days. Also the heat loss is into the fabric of the building, and so offsets the load on the heating in the winter.

although possibly a bit more noisy...

It also assumes decent mains pressure. Not the case in this part of London.

The circulation pump would normally be on a timer.

Although for filling a bath then there is the old fashioned way of putting in the plug, turning on the hot tap and letting the first few litres of cold water go into the bath before the hot water arrives and mixes with the cold water.

Asssuming you do not have a back boiler or a combi, in which case there isnt any *hot* water. Just a slow trickle of slightly warm water.

I have torrents of hot water - enough for 2 bathrooms. But I did not cheap out when I got mine.

The only real "fault" in a combi that I have observed is that if you have a run on baths in the morning (like 3 end to end) you of course lose heating.

But having mains pressure hot water, endless hot water and no storage tanks makes up for it.

Just what I was going to say. DAMHIK.

Hot water any time you like. Hot water with no delay when the timer is active.

Lag it dear liza ;-)

You don't... use some that is "good enough". Deduct the heat lost from your space heating requirements, and accept that there is a price to pay for added convenience.