2 Combi Boilers in one house?

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Hi All,

I've got a customer who wants 4 showers in one house. They don't want electric showers, so I guess it'll have to be a big cylinder. But would it be possible to put 2 combi boilers in, so as not to have to store hot water? I assume the cylinder would need to be quite big for 4 showers, and would take longer to warm up after it had been emptied. So I'm exploring the possibility of putting in 2 combi's. Would I need to get the regulator on the meter changed? (The hob and oven will be all electric).

To avoid a complicated job on the central heating, I could have just one combi for the heating and say 2 showers, and the other combi for the other 2 showers. Or would it be best to plumb the boilers in unison with a separate cold feed for each. If I put a non return valve on the hot coming out of each boiler, the pumps won't be fighting each other.

I did consider solar panels and a big cylinder as another option.

Any and all opinions very welcome. I know a little bit about boilers, but I guess that just makes me dangerous!
 
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Two combi boilers each capable of supplying two showers would certainly need the gas supply upgrading.

Stored hot water in a cylinder would be the better option.
 
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Thanks everyone for the info. I reckon it'll be more straightforward to store the hot water, there's less to go wrong!
 
The flow rate coming in is the deciding factor. 70kW should be enough, but the water pressure could be too low for all 4 showers at once, I hadn't thought of that one, cheers
 
Best option is an unvented cylinder and an accumulator to ensure enough flow rate for all showers
 
The key point to any solution you implement is the incoming supply - Dynamic Flow rate and pressure - The minimum I would suggest for 4 standard showers would be 3 bar dynamic @ at least 30L/Min from the mains. When it comes to that many showers then you need to gauge dynamic reading with at least 3 full flowing outlets open.

Distribution pipework - really needs a min of a 22m backbone before branching to each shower and smallest drop to 15mm

I have a 22mm supply and distribution pipework to 3 normal thermostatic bar showers (only the last 500mm is 15mm). My supply runs @ 3 bar dynamic @ 28L/Min (4.5 bar static). 180L unvented with high recovery coil on a 32Kw system boiler. There is a little drop off of pressure when all 3 are running but it will happily supply all 3 showers at the same time.
 
Can you still buy a DHW boiler? I know my old house had a Main 7 DHW boiler for domestic hot water and a completely different boiler for central heating, installed in the 80's, but having two boilers for central heating seems wrong.
 
You can still buy gas water heaters but they are not the solution for this problem.

To try to supply four showers the key factor is the incoming water supply dynamic flow rate.

An unvented cylinder heated by a single gas boiler would be the best solution.

I would always want to use a 300 litre cylinder so that there is plenty of capacity for stored hot water.

If the incoming water supply is rather inadequate then an accumulator could be used but this needs to be very carefully sized to be effective.
 
I would always want to use a 300 litre cylinder so that there is plenty of capacity for stored hot water.

Or maybe ( lateral thinking ) two smaller cylinders, one supplying the two family showers most often used and the second one that supplies showers used by overnight visitors / guests and only heated when there are overnight visitors / guests staying in the house.
 
The heat loss of a 300 litre cylinder is minimal.

Certainly not worth the extra costs and heat losses from pipework and controls on two cylinders.

The other advantage of a large cylinder is that it can be set to not use so much input from the boiler so that it does not prejudice CH performance while reheating hot water.

The best performance is obtained by timing the hot water heat up just before the CH "on" time.
 

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