using combi with seperate hwc for bathrooms

[gordyc]

Hi there all!
Looking for guidance on the topic above. I have 4bed 1 bathroom 1ensuite showeroom. 32 year old Ideal Mexico RS65 (19kw) system boiler is still going strong but I'm aware its probs on borrowed time now. CH/DHWis a vented system with CH feedtank and DHW storage tank in the loft, the latter feeding the HWC beside the two loos. Boiler is sited at kitchen end and HW is a long run from the HWC, therefore losing heat on the way through.
As part of a planned upgrade to all of this, I'm thiniing that there seems to be no obvious reason why I can't use a similar sized Combi replacement to feed the kitchen and utility hot water demand and the CH system with the HWC simply connected, as it currently is, like a radiator Teed into the feed with a separate return. I'm keen to get rid of the loft tanks altogether, so a sealed mains supplid tank sounds like the solution but I'm not familiar with these. They became very popular back in the 90's but I've heard mixed reports about them.
I do like the idea of having the benefit of mains pressure in the loos for the shower and bath but it's a bit more complex than my 30+ year old installation when I built the house originally.
Any advice from anyone who has tackled something similar would be gratefully received.
Cheers
Gordy

 

[gordyc]

Should point out that property is a bungalow!!!

 

[oldbutnotdead]

Yeah that'll work- considering doing something similar after a suggestion from a member on here. Check your mains water pressure and flow rate before investing in a pressurised cylinder- can't remember what the golden numbers are but if you search this section you'll probably find them. An incidental bonus with your plan (provided mains pressure etc is good and you have a 22mm cold feed to the cylinder) you'll eliminate a lot of the flow drop to shower users when someone turns the kitchen tap on

 

[gordyc]

Mains pressureup here in Scotland isnot an issue. It rains hard enough to run the system!!
Yes 22mm feed along to a cylinder would be simple to do.
Have you given any thought to a suitable boiler? I was thinking that, as I wouldn't need high flow rate hot water in kitchen and utility then a lower rated combi would still be able to run the CH easily. The old RS65 is only ever turned up above 1 in the sub zero spells between now and end of March, so something around 20 -25kw should pack more than enough punch and cope with the hot water demands of the cooking and washing up. The washing machines are all cold fill these days as are dishwashers, so there's little call for gallons of hot water there.
Another benefit of the HWC is that I can keep it turned down with the thermostat until just before demand is needed, then boost it either with the boiler, or use an electric immersion heater. I'll have an unused shower circuit available to run that!
I also would like to move to a wall hung boiler from the old floor mounted Mexico, to free up that space in the utility room. Had looked at Worscter bosch system boiler before asking about the combi use in this thread. Their eco greenstar 25i looks man enough for the job.
Cheers and thanks for your input.
Gordy

 

[oldbutnotdead]

If you want the hwc to work that way you'll need its feed and return coming off the main heating run before any radiators (if there are already separate 22mm F & R to your old boiler for hot water then use them, that'll be perfect with a zone valve). The boiler will be much cheaper and quicker at boosting the cylinder temperature, you will find that a modern cylinder with hard insulation on will retain heat much better than your old copper so having hot water on constant won't be much of a cost.
Boiler size depends on your house size,, insulation etc- there's loads of heat loss calculators on the web, do some sums and see what the theoretical load is for your place. In a combi as far as I know there is a separate heat exchanger for the DHW & I don't think the HW output is included in the headline number but yeah any combi will manage a kitchen and utility room tap. Have a look at Intergas