Pipes likely to be a problem for an upgrade to a combi?

[Keith G. Powell]

I am considering upgrading my 1980's central heating to use a condensing combi.

In the loft of my bungalow, there are water tanks for the heating and shower, as well as a pump, 2-port valve and a manual valve to isolate the the heating coil in the hot water tank below in the airing cupboard. All of these will be removed.

The pipes to and from the current boiler in the garage are 22mm. They go up to the loft then down from the loft back into the garage where they go into the concrete floor for distribution to the radiators. At some place in the concrete, the pipes change to 15mm for distribution to the radiators. In the concrete near each radiator, there are two inspection plates which gives access to the pipes. The 15mm pipes T-off(soldered) to about 6 inches of 8mm pipes which finally connect to the radiator valves.

Is this pipe-work likely to be a problem for a condensing combi?

Keith G. Powell

[Christian McArdle]

No. Indeed, a condensing boiler can cope with smaller pipe sizes than a non-condensing one. This is because they are designed to cope with a larger temperature differential between flow and return. This means that with a constant velocity through the pipework, more energy is transferred, as the energy transfer is directly proportional to the product of water velocity and temperature difference. The water velocity is limited by the power of the pump and the need to reduce noise.

Obviously, you'll need to remove all the tanks and run the system as a sealed pressurised primary.

Christian.