Instant Hot Water

[oldbutnotdead]

Soz for causing confusion- my luxury option (looped dhw from storage) would work if you had a hot water tank on the heating side of the combi.
I have one of those 9kw heaters- it serves washbasin and kitchen sink nicely but shower flow is a bit weak in the winter (when ambient water temp is low).
Your combi will run a shower quite happily & gas at the moment is about 1/4 of the price of electricity per kwh.

 

[MisterFish]

Soz for causing confusion- my luxury option (looped dhw from storage) would work if you had a hot water tank on the heating side of the combi.
I have one of those 9kw heaters- it serves washbasin and kitchen sink nicely but shower flow is a bit weak in the winter (when ambient water temp is low).
Your combi will run a shower quite happily & gas at the moment is about 1/4 of the price of electricity per kwh.

Okay. Thanks. Can you point me at somewhere that can give me some idea how to do that please?

 

[oldbutnotdead]

A hot water cylinder with a coil inside behaves like a radiator- coil gets hot, heats water in cylinder. Ideally you'd zone the system (using motorised valves) so you can have hot water or heating or both. Very simple standard stuff. You'll need a header tank with your cylinder of course, header wants to be as high as possible to give good shower pressure. Or look at shower pumps and Surrey flanges or pressurised cylinders (not DIY and may not be suitable if mains flow/pressure is low). The cylinder can be near your upstairs bathroom (to reduce time to hot) so you wouldn't necessarily need the dhw loop, if you do there are specialised pumps that learn your routine and optimise the loop circulation for most economic and quiet operation.
Any competent heating installer should be able to go into more detail about all this- @Dan Robinson is a mine of information.

 

[MisterFish]

Okay. Thanks. I'll certainly look into this one.

 

[bernardgreen]

Or look at shower pumps and Surrey flanges

An alternative for having mains pressure showers is a second coil in the top of the cylinder to heat mains pressure water using heat from the water in the cylinder. Does not require any shower pumps. The second coil is the green/orange item.

Low pressure hot water for taps and basins is supplied from the cylinder.

 

[oldbutnotdead]

@bernardgreen 's option is also available and an excellent compromise-gives you mains pressure hot water without the expense of a pressurised cylinder. Again simple plumbing-wise but i believe to comply with water regs/bylaws you'd need a backcheck valve in the cold feed to the coil and a pressure relief valve in the output circuit somewhere.

 

[bernardgreen]

comply with water regs/bylaws you'd need a backcheck valve in the cold feed to the coil

Expansion back towards the mains is acceptable ( conversation with WRAS ) provided that :-

a) the volume in the second coil is less than 15 litres
b) the expansion volume is less than the volume of the pipe between coil and nearest T feeding a cold water tap ( ie expanded water does not reach a drinking water tap )

 

[oldbutnotdead]

Expansion back towards the mains is acceptable ( conversation with WRAS ) provided that :-

a) the volume in the second coil is less than 15 litres
b) the expansion volume is less than the volume of the pipe between coil and nearest T feeding a cold water tap ( ie expanded water does not reach a drinking water tap )

Ah, that's useful- ta. I assumed there would be a backcheck valve at the street stoptap so back expansion might push pressure up quite a way...

 

[bernardgreen]

Just to add.... the cost ( delivered ) of the bespoke cylinder with added coil was considerably less than the cost of an un-vented pressurised cylinder.

The one error ( minor ) was overlooking the fact that the volume of water ( as heat store ) was reduced by the volume of copper forming the second coil.

 

[Tangowagon]

One 3kw instant heater could feed two hand basins, if it is supplied by mains pressure, run the supplies to the basins in 10mm plastic microbore, the flow will be adequate and less volume in the pipe will mean less time to get hot water at the tap and less waste. I plumbed up 3 holiday cottages running off a central unvented cylinder in this manner, bathrooms in 15mm, kitchens in 10mm, all plumbed back to a manifold on the tank.