Combi boiler + pump + shower setup question

[austin99]

Hi there,
Currently getting a house refurbished (and properly insulated) with a new CH system. Have very basic hot water requirements (there's a Triton electric shower there already) so was going use a combi boiler and get rid of the old hot water cylinder to get a little bit more storage space;

However currently thinking of ditching the electric shower and putting in a regular one. The plumber has proposed the following but I'm getting mixed messages as to whether this is viable or not.

He's saying to install a 2 bar pump downstairs (Nordic 250) which is gravity fed from the cold water tank in the attic and use that circuit for all hot water including the shower. The shower is upstairs by the way.
Also to use a higher spec boiler Greenstar 32CDi (instead of 24i) combi which can supply 13 litres/minute of hot water.

Does this sound viable? Are there any caveats with this apart from ensuring that the shower doesn't exceed 13 litres/minute?

I talked to another installer and he advised against this setup and said to either use an electric shower or a traditional heating system with hot water cylinder - but I definitely just want hot water on demand, hence a combi system.

CH heating requirements are;
2 bedrooms, 1 bathroom, 1 wc, living area/kitchen (open plan), hall/stairs/landing
= 7 radiators, about 8kw (27k BTU)

Thanks!

 

[picasso]

What is the flow and pressure of your incoming water main ?

 

[austin99]

What is the flow and pressure of your incoming water main ?

Plumber tested it and said it was quite low - sorry I don't have the psi/bar figures.

Also I don't think you are allowed to put a pump on the mains supply (in Ireland). Even it was possible I don't think I'd want a pump coming on anytime water is used in the house due to the noise

 

[picasso]

Who said anything about pumping the mains ? yes its viable to use a pump on your combi, as long as you dont mind the noise of the pump every time a tap is turned on.

 

[austin99]

Who said anything about pumping the mains ?

Ooops, sorry

as long as you dont mind the noise of the pump every time a tap is turned on.

I don't mind the pump coming on for just the hot taps & shower.

Regarding the shower - is it likely that any shower that says compatible with combi boiler would be suitable, like this one

 

[austin99]

Regarding the shower - is it likely that any shower that says compatible with combi boiler would be suitable, like this one

Could someone offer some advice as to what size cold water tank I'd need if I was using a shower such as this - say the shower runs at 10 litres per minute. Is there a rule of thumb for sizing the cold water tank based on that flow rate?

Thanks

 

[shray]

It does sound like a viable setup, one which I've never come across before, however I think the problem is that the mixer shower needs to have balanced hot and cold feeds so putting a pump on the hot only will cause problems. You could put a pressure regulator on the cold to the shower I guess to overcome the problem but it's not really textbook plus if another hot tap is running at the same time it will become unbalanced again.

I would just opt for the combi without a pump personally. Surely the incoming mains must be more than 2 bar ?

 

[picasso]

I assumed that the plumber would pump the whole house, bit pointless just doing the hot, as a rule of thumb a 50 gallon cold water tank would do a 1 bathroom property.

 

[onlyfitidealboilers]

Surely you mean put a pump on the cold feed from the domestic tank to pump it through your combi there for giving 2 bar hot water.

Cold main to taps could stay in the main or also be pumped.

In the case the MAIN is not pumped you would need a balancing vlv to the shower / mixer taps.

 

[austin99]

Surely the incoming mains must be more than 2 bar ?

It's just 0.6 bar!

 

[austin99]

I think the problem is that the mixer shower needs to have balanced hot and cold feeds so putting a pump on the hot only will cause problems

Plumber is planning on also pumping the cold feed to the shower. So the hot and cold feed pressures to the shower will be balanced (at 2 bar)

 

[shray]

Thats **** lol. Just another thing to bare in mind if the incoming is only .6 bar.....how do you expect to fill the heating system to the required pressure ?