2x Mixer Showers, 1x Combi Boiler

[Ian Turner]

Hi,

I have a property with 2x Mixer Showers being fed by a worcester junior combi boiler, as you can guess this means the showers don't operate correctly when they're both turned on at the same time.

I'm in the process of upgrading the system and would like would advise from those in the trade as to what would be the best option as I've have 3x different options presented to me thus far.

Thanks,

 

[bernardgreen]

The tradesperson doesn't have to live with the system he installs in your house. As you have found a combi boiler and 2 showers is not a good combination. Yet some tradesmen still advocate combi boilers. Ask what they have in their own homes.

Provided the incoming water supply is adequate then a hot water cylinder can supply 2 showers and does not need a high power boiler to heat the water. A combi boiler that has enough power to run a single shower ( typically 36kW output ) is invariably too large to efficiently run the heatng system ( typically 4 kW ). Some boilers can adjust their output power but efficiency at one end of the range can be lower than expected.

 

[Hot&Cold]

what would be the best option as I've have 3x different options presented to me thus far.

Three different opinions and now a Fourth from Bernardgreen What else do you want to know

Have you had an onsite survey to discuss your demands and needs,without seeing your property i would estimate you need to 'splash' out around £3k +vat more in London

 

[oldbuffer]

Presumably the options are:

1. Replace one of the mixer showers with an electrically heated shower.
2. Install a vented hot water system, with the hot water cylinder (HWC) heated from an extra zone from the central heating. One shower off combi hot water, the other off a (pumped?) supply from the HWC.
3. Install an unvented hot water system, with perhaps both showers of the unvented cylinder (no pump needed) but the kitchen hot off the combi hot water.

I'd see the benefits and pitfalls as:

1. Electric shower:
1a. For:
Probably minimum disruption to existing system.
A source of hot water in the event of boiler breakdown.
1b. Against:
Extra wiring and (possibly additional) consumer unit.
Generally poor flow rate.
They don't tend to last all that long - in my experience you'd do well to get 5 years regular use out of one.

2. Vented hot water system:
2a For:
Relatively simple provided you've got the space for a HWC and a cold water storage cistern (CWSC) which need to be as far as possible above the HWC.
With an immersion heater fitted you've got a source of hot water if the boiler breaks down.
No need for an annual service.
If the water supply is interrupted you've got a store of hot and cold water.
Can be fitted by any competent plumber.
2b. Against
Installation could need a fair bit of extra pipe-work.
You'd probably need a shower pump to provide sufficient pressure to get a decent flow rate.
Space taken up by HWC and CWSC

3. Unvented hot water system:
3a. For:
If you've got the pressure and flow rate it gives you mains pressurised hot water everywhere without pumps.
No requirement for a CWSC
With an immersion heater fitted you've got a source of hot water if the boiler breaks down.
3b. Against:
Installation could need a fair bit of extra pipe-work, but probably not as much as vented hot water.
Space needed for HWC and a few ancillary bits.
Must be installed by a plumber / heating engineer with a current "G3" qualification, who should also notify your local building control department.
Needs an annual service.

My personal choice, in order of preference, would be the unvented hot water system, an electric shower, a vented hot water system. Your preference will probably be different, but if there is no airing cupboard space or loft, you could probably rule out the vented hot water system.

As a final thought, it might be possible to replace the boiler with one which has a store of hot water (a sort of hybrid combi with small unvented HWC). How suitable would depend on the length of showers taken. You might get two quick (5 minute?) showers off the store, but you almost certainly wouldn't get two 15 minute showers. Also depends on the flow rate and temperature of the showers.

 

[John D v2.0]

Another option is keep your existing Combi and splash out the best part of a grand for this http://powerpipehr.co.uk
Basically a heat exchanger for your stack, so the water coming in is heated by the water leaving.
Should according to their test results double the shower capacity of a given boilerboiler s to incoming flow.
I've never used one but I'd consider it before replacing a service able Combi partly to the gas saving.

 

[bernardgreen]

Three different opinions and now a Fourth from Bernardgreen

My opinion might be the same as the opinion from one of the three.

Should according to their test results double the shower capacity of a given boilerboiler s to incoming flow

It will not increase the maximum flow if hot water from the combi, That is set by the pressure regulator and the resistance to flow through the heat exchanger. It might enable the boiler to produce water as a slightly higher temperature by pre-warming the wate going to the boiler. It will increase the resistance to flow and hence the amount of water for the shower(s),

 

[John D v2.0]

It will not increase the maximum flow if hot water from the combi, That is set by the pressure regulator and the resistance to flow through the heat exchanger. It might enable the boiler to produce water as a slightly higher temperature by pre-warming the wate going to the boiler. It will increase the resistance to flow and hence the amount of water for the shower(s),

Correct apart from you said slightly higher temperature but the manufacturer claims 50% recovery although I'd have to recheck the conditions for the test.
As I said it's subject to incoming flow, this would apply regardless whether it's a bigger Combi or smaller one with heat recovery.

Good point about extra restriction of the unit itself, I'm not sure what that is ifo hand.