Immersion Tank with Combi Boiler...

[Christian and Beccy]

Following on from something that was raised in another post, I'd greatly appreciate a bit of guidance.

I have a fairly hefty Combi Boiler. I also have 4kw of Solar PV, which I feel I should be utilising to heat hot water during the day.

Could it be viable to install a Hot Water tank/Immersion whilst still running the Combi boiler? If so, I'd appreciate a bit of a laymans explanation so I know what to expect...

 

[OwainDIYer]

You can.

The hot water cylinder would be plumbed to the combi boiler as a second radiator circuit (S plan plus) with its own timer/thermostat controls. You'd might need to disable the boiler internal controls or set it to 24 hour, so you might need additional controls for the existing heating system.

Typically you'd use the hot water cylinder HW for baths, and keep the combi hot water for a mains pressure shower or for kitchen hot water.

I don't think you can mix combi (instant) hot water with cylinder hot water though - they'd have to go to separate taps.

 

[Christian and Beccy]

OK, so I could possibly overcome a fundamental problem I have in my main bathroom at least.

I (stupidly) ran 22mm pipes to the Bathroom, which are now all concealed. So, whilst the bath fills very quickly, if you want hot water at the basin, it takes forever. In fact, for hand-washing you might as well just use the cold tap!

Perhaps I could use the hot water tank to supply that Bathroom entirely and keep the Combi supplying the En-Suite and Kitchen?

 

[JohnD]

because energy from gas is only one-third the cost of energy from electricity, the amount of money you save by using solar for HW will not repay the cost.

For example, my gas bill, for hot water only once the heating is off, last August, was £6.79 for gas used, and £7.75 standing charge. If solar had saved me half that usage, it would be less than £3.50 per month.

If you already had a cylinder, with immersion heater, then it would do no harm to heat it from solar in summer. A solar controller (to supply the immersion heater when there is spare power generated) costs about £200, so it would take at least seven years to repay the cost. If you paid for controller + cylinder + electrical + plumbing work, it would be a moneywaster.

In winter you might get an average of 5kWh per day from a typical solar installation, and most of it might be used in your background electrical useage, so little excess to spare. 5kWh of gas would cost you about 20p

If you had no gas, and paid expensive electricity prices for all your energy, the savings would be better.