large 6 bed house with 2 bathrooms 2 kitchens a wc. what boiler do i need?

[Z. RANA]

I have a large 6 bed house with 2 bathrooms 2 kitchens and 1 down stairs toilet.
+ 2 large living rooms.
15 / 16 good sized radiators and currently have worcester 28 Si II boiler. At 80% efficiency it is D rated. We use gas not LPG.

But need to change it so a good time to upgrade to one with higher effieciency and more power and much better water flow.

What will be a good boiler to upgrade to. British gas guy said 31 cdi or even 37 cdi will be good. but iv looked and even the 37cdi is for upto 5 bedroom and 1/2 bathroom.

my loft is insulted to about 200mm knauf wool on the floor and about 150mm knauf on the roof along with one layer of insulation foil and some loft boards in the centre of the roof.

Also we have insulation between the cavity walls + double glazing.


Bedroom Room 1 size:
L3.45m * W3.40m *H2.34 = 27.45m3
radiator size: W0.8mm by H0.6m semi double = btu

bedroom 2 size:
L3.45m * w3.10 *h2.34m= 25.03m3
radiator size: 1.0 *0.60m single= btu

bedroom 3
w1.96m* 3.54m *2.34=16.24m3
radiator size: 1.0 *0.60m single= btu

bedroom 4
w1.96m* 3.54m *2.34=16.24m3
radiator size: 1.0 *0.70m semi double= btu

bedroom 5 size:
L3.05m * w3.64 *h2.34m= 25.98m3
radiator size: 1.0 *0.60m double= btu

bedroom 6
w3.18m* 2.08m *2.34=15.48m3
radiator size: 0.8 *0.60m double= btu

bathroom 1
w2.80 * L2.10m *2.34 = 13.76m3
radiator size w1.20m * 0.6m semi double.

bathroom 2 (ensuite)
W0.8m * H2.10m * H2.30m = 3.87m3

living room 1
W3.45 * L6.65m * 2.34mh =53.68m3

2 radiators
2 * w2.07m h 0.3m semi double=

living room 2

W3.96 * L3.40m *2.34m = 31.51m3
radiator size: w2.30 * h0.30 semi double=

kitchen 1
W3.05m * 3.64m *2.34 m = 25.98m3

radiator size W0.8m * h0.90m double=

kitchen 2
W1.80m * L2.95m * h2.34m = 12.43m3
radiator
0.6m * 0.6m double =

down stairs toilet
W1.15m * L1.55m * h2.34m = 4.17m3
no radiator but panel electric thermostatic heater.

store room
1.15m by 1.35m *2.34m = 3.63m3
no radiator but panel electric thermostatic heater.

corridor radiators:
radiator 1 = W0.4m * H 0.9m double =
radiator 2 = W0.6m * H0.9m double =
radiator 3 = W1.2m * H0.6m double =

currently we have a worcester 28 si II boiler. a british gas guy said you need a bigger boiler as the 28 Si II is for e.g. a three bedroom house. and you can easily upgrade to a 31cdi or even a 37cdi. i need some guidance as to what is best.

(We have 6 bedroom with 2 showers and 2 kitchens and one more down stairs toilet. two of the three toilets are fitted with a muslim shower and thermostat.. obviously they are only used for a few seconds so is not the main concern.. )

we noticed our main use is hot water as the pressure drops when two showers are on and due to 2 kitchens and also a downstairs toilet that we need hot water at certain times.

i am not sure how many liters per minute the 28 si II boiler provides so how much an upgrade will improve the flow by.

i can upgrade more pics or exact btus of radiators if needed.

 

[endecotp]

Do you have space somewhere for a hot water cylinder?
How important is it to be able to supply both showers simultaneously?
Is the house, or parts of it, cold during cold weather?

 

[Z. RANA]

currently we also have electric showers installed in both the bathrooms. i.e 1 9.5kw electric shower right next to hot water supply. they are as a back up to the combi boiler, and the combi boiler is a back up to both the electric showers. the system has worked well in case of failure to either the gas boiler or the electric showers.

in actual practice one bathroom uses the electric shower whilst the other (my ensuite) uses the combi boiler shower mainly, as i find the pressure and speed of the water coming out is much better then the 9.5kw standard electric shower. it gives me a better clean.

the problem tends to come when I'm having a shower and my wife is washing in the kitchen, and if another hot tap is also in use in the house, thus makes it worse still. it could be from the second kitchen, upstairs sink or the downstairs toilet. but this problem is only for 5/10 mins when either one person finishes the shower or one person finishes the washing up. but if 2 or more hot taps are in simultaneous use and also the (one) shower then it doesn't work (at least for 5 mins.. ). the (old D rated, only 80% efficient) boiler i feel is under load... starting and stopping...

if the 28i II supplies about 10.3 litres per min, i think an upgrade to 15/17 L/min could work. as the problem is normally not more then 5-10 mins...

as for space in the house its limited and we have ample space in the loft, but the extra work involved in doing all this (i.e installing something in the loft) i don't think is worth it as the problem is not that severe or that common. but it is there. and since we are getting a brand new boiler free of charge (from British gas) then its good if i do some homework to make the right choice.

one or two rooms may be slightly cold during very cold weather as they may be empty. the washing machine room store was freezing as it had a vent hole in it , but iv blocked this and the problem has gone.
There are electric panel (thermostatic ) heaters in the second smaller kitchen and downstairs toilet, where there are no radiators.

I installed some big radiators in the corridor and upgraded some radiators to big double ones and any cold areas are eliminated. we also have electric panel heaters as a backup to failure of the old worcester boiler. they have come into play when the boiler plays up every few years. Iv had insurance and worcester fixes the problem with brand new parts and 12 months warrantee but after about 2 years. or when the warranty expires (typical) the boiler breaks down again. the boiler is now 13+ years old and D rated at 80% efficient only. so a full upgrade to a high efficiency is i think overdue.

the gas man said that with the worcester si he has seen many problems with but the cdi model is in his view not many problems. so that information i really value.

 

[Mikefromlondon]

why not fit two boilers one in each kitchen and split hot water and CH between the two and something to fall back on if one breaks down, since you have two kitchens and two baths, and so on. Decide how best to split the two if you decide to split the house in two 3 bed houses. (only a suggestion)

 

[Razor900]

How come British Gas are giving you a free boiler? Seems very generous of them!!

 

[Dan Robinson]

why not fit two boilers one in each kitchen and split hot water and CH between the two and something to fall back on if one breaks down, since you have two kitchens and two baths, and so on. Decide how best to split the two if you decide to split the house in two 3 bed houses. (only a suggestion)

Idiot.

 

[bernardgreen]

How come British Gas are giving you a free boiler? Seems very generous of them!!

Maybe the boiler comes "free" and the installation is charged for a price that covers the cost of the boiler.

Idiot.

That is your opinion, care to give an explanation why it is (in your opinion ) idiotic to have two boilers ?

 

[Dan Robinson]

It's been covered before.

 

[DaveHerns]

What's a muslim shower?

 

[Dan Robinson]

Door faces Mecca

Actually they are against the water regs, so the less said by the OP the better.

 

[hazetimesfive]

stop being a douche dan

 

[Z. RANA]

why not fit two boilers one in each kitchen and split hot water and CH between the two and something to fall back on if one breaks down, since you have two kitchens and two baths, and so on. Decide how best to split the two if you decide to split the house in two 3 bed houses. (only a suggestion)

Maybe I could. Good idea, my brother had two in his building and i saw it work well. For commercial situation it is a clever idea. But in this ( domestic ) case it's too expensive (I think).

1) I'll have to pay for the second boiler my self, don't want to do that... Plus it might mean two lots of things to maintain and insure in the house. Even more expense.
2) don't have anywhere to put it, unless I loose a cabinet, which I don't want.
3) will require a lot more work, thought and maybe an overkill
4) the old 28kw (si II at 80% efficiency, D rated) combi was doing well till now (except for hot water at some short times during the day). At only about 10.3 L/min. I can see why. An upgrade to a different model CDi and at 90.5% efficiency, A rated). to 32kw = 13.1 L/min or better still 38kw = 16.4 L/min, I feel may do the trick.

 

[Z. RANA]

What's a muslim shower?

Muslim shower = Is a bidet. Ie hand held water spray.

A spray that is used to clean (mainly) the backside after excretion as well as the toilet itself. The jet wash action cleans faster and it feels more cleaner afterwards. Like a power washer (although not as powerful) to wash parts of your body.

You gotta try it, but make sure you set a thermostat, as if it's only on a hot tap it might burn you!

 

[Mikefromlondon]

Hi Rana, for that sort of flow rate 16L/m, you will need to check that your mains pressure and flow can supply you that to start with, or you will be going for too big an appliance.

One other suggestion is to fit flow restrictors in hot water pipes to kitchen so that if it is opened fully it restricts hot water flow to say 5 or 6 liters per min, that way extra water needed upstairs will be there. You may need to change the size of your gas pipe for a bigger boiler even if you had two boilers you would still need good gas flow for higher rated boilers, as well as your incoming water pipe sizes if your flow rate is lower than what you need.

 

[Z. RANA]

How come British Gas are giving you a free boiler? Seems very generous of them!!

Well if it sounds too good to true it prob is. I'll wait and see how much I actually have to pay. Nothing is free. There has to be catch. I'll wait and see. But I'm not expecting (at least ) everything to be free. It can't be.