What is the best and most efficient system to install?

[davidk2612]

Hi, wondering if anyone can help...
I have just bought a house and am planning to add a two storey extension which will include a bathroom, two en-suites and a downstairs wc.
I have heard that the best and most efficient option is to install a pressurised hot water system with a 24kW boiler, but much depends on the mains pressure?
I would like the main shower to have some gutts so would like this off the mains, but want the system to be able to cope with a decent shower, a bathfull of water (we have small children) and another shower maybe within an hour...
Also don't want hot or cold water pressure to reduce to nothing if two taps are open or shower and tap etc.
Is it best to have all mains showers or a mixture of mains and electric?
Also is 24kW enough to re-heat the tank and serve what will probably be 12 radiators in the winter...
Also, ecconomy is important...not sure if i can have my cake and eat it...HELP!
All suggestions welcomed!

 

[bengasman]

The performance of an unvented system depends on a sufficiently large incoming mains, if you want to go this route, that is the first thing to check and upgrade.
A 24 kw boiler will produce in excess of 500 litres of hot water per hour.
The difference between the "best" and "worst" performing a rated boilers is negligible.
Whether or not 24kw is enough to serve 12 rads depends on the size of them, but it will probably do fine.

 

[mickyg]

All of your requirements seem to centre around feeding a number of hot water outlets posssibly at the same time. For this you need a good flow of water from your main supply. First job is to measure this to find out what your options are. An easy way to do this is by filling a known volume and timing how long it takes(eg 10litre bucket). work out your l/min and go from there.

 

[davidk2612]

Thanks chaps, I thought it might...
Will do the volume/min test this weekend and find out, what is the min I'm looking for and what can I do if insufficient?
Also, any comments ref: mains/electric showers, or does this depend on above?
Finally, again assuming pressure good, what size tank do you recommend?
Cheers again...

 

[bengasman]

The minimum depends on how many showers/taps you want to be able to use simultaneously. Decent shower needs about 15 l/min each, bath 15-20, basin/sink 5-10.
Good quality cylinders are well insulated hence a bit more than you need won't hurt in use.
If the flowrate is not high enough, you need a bigger pipe, simple as that, and all the way from the streetvalve to the cylinder/bath.
What you want is gonna cost a few bop, I hope you budgeted that in.

 

[Deleted member 105431]

If you have good mains pressure and the cash a rinnai twinflow would be a good option.

http://www.rinnaiuk.com/Updates-18-09-08/A4 Twin Flow.pdf

 

[fitz1]

with so many bathrooms i would have one electric shower and would put a hot return to the cylinder (a hot loop from cylinder and back to cylinder with short legs off it to your outlets)

 

[mickyg]

if you've got 20 l/min+ that should pave the way for an unvented, highflow combi or if you speak to Mr Bramwell a Thermal Store
Everyone will have an opinion and they will all vary, but I'll give you mine anyway ... Depending on your usage I would probably recommend a GW Ultrapower 170. It basically combines an unvented with a combi boiler. It has all the advantages of an unvented cylinder, including immersion backup, but the added advantage that at a limited flow rate it will never run cold at high use times, although this is unlikely as the reheat time is very quick. Its also all in one box so it saves space and keeps things compact. Like I say this is just 1 opinion, also DMs suggestion of the Twinflow system is also very good.