showers and hot water systems

[CT]

We have a 3 storey Victorian house with 2 hot water systems - a tank (heated by an AGA) that provides hot water to the top of the house and a new combi (Worcester Bosch, fitted by British Gas last Sept) that heats the radiators and provides hot water to the lower parts of the house. We are having a new bathroom fitted and the plumber said that the boiler was stretched when he started and could barely cope with its exsiting demands of 17 radiators, 1 mixer shower and hot water to the kitchen/ 2 sinks (plus dishwasher and washing machine). The hot water tank provides water to another ensuite (inc a shower, no bath) and several sinks (4). I understood the new bathroom was to be plumbed of this tank - power shower (has deluge head and diverter), sink, large bath. However, he now plans to plumb the 'power' shower off the combi. I am very concerned that this is not going to work, and I will be left with a system that does not work well. What is the best solution? Thanks

[Mark Hewitt]

I thought power showers were pumped and hence couldn't be used from a combi?

[dom]

I'm no expert on plumbing - but I wonder how he's certain the boiler is being overstretched?

Yes, you have a lot of radiators, but if they're keeping you warm in winter and the duty cycle on the boiler is OK - is there a problem?

I'm not clear how much of your hot water is coming from a tank running from your boiler and how much straight off the combi part?

Again if your hot water reservoir is sufficient to keep up with peak demand, and the recovery time is acceptable to you - is there a problem?

I also thought power showers were incompatable with combis?

[CT]

If we have 2 showers off the combi - can they be used at the same time?The present shower off the combi has adequate pressure/flow but this does drop if a tap is turned on elsewhere. The combi supplies 4 sinks (inc kitchen) and 1 shower. The tank supplies 4 sinks + whatever we use it for in the new bathroom

[John Rumm]

How powerful? (i.e. which model)

If he is talking about a pumped shower, then no you can not use this on the HW output of a combi, since you will be in effect pumping water from the mains.

If your showers are using drencher type heads I would also be very skeptical of the combi having the flow rate to cope with both at once.

I would have thought one shower on the combi, and one from the stored water system with a pump if you need a pressure boost.

[John Rumm]

It sounds like you ought to do some heat loss calculations for the house to work out what power of boiler you actually need, rather than relying on the plumbers guesswork. Have a google on this group for information on how.

[Mark Hewitt]

Usually the answer is no. Obviously they can be used independantly from each other buy unless your combi is massive it won't be putting out enough to run two showers at once.

[David Hansen]

On 11 May 2006 01:27:31 -0700 someone who may be "CT" wrote this:-

The best solution probably involves people looking at your house in some detail and doing a lot of calculations.

I doubt if a combination boiler is going to cut the mustard producing all that hot water. What I would look at is buying a solar hot water cylinder, and using one of the coils for heating it from the AGA and the other for heating it from the boiler. There are some photographs at

to give an idea. Note that these can be supplied with extras like more coils and show bosses.

The size of the cylinder would depend on estimated demands and the ability to re-heat the cylinder. It might also mean looking at the tank in the loft that presumably supplies the current cylinder and perhaps enlarging it and the pipe supplying the cylinder.

There are suitable control systems. One way of using these might be to give priority to the AGA and only use the boiler when this was not supplying enough heat.