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

[Agile]

4) the 28kw combi was doing well till now (except for hot water at some short times during the day). At only about 10 L/min. I can see why. An upgrade to 32kw = 13 L/min or better still 38kw = 16 L/min, I feel may do the trick.

If a 28 kW boiler gives 10 li/min then I don't see how your 32 kW is going to give much more than about 11.5 li/min.

 

[Z. RANA]

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.

Yes, good reply. Probably the most thought provoking reply so far. Well done!

Iv got taps ( water restrictors) in every tap of the house. Both on the cold taps and hot taps, on the bidets and on the showers and pipes going up and for the pipes on the ground flow. This helps to isolate any tap if there is a leak, (to isolate any potential leak) or adjust water output as desired. Basically every water outlet there is a tap which I can open or close or adjust the speed of out coming water at will.

Iv adjusted all the hot water taps in the kitchens / basins to about 3/4 full that's about 7L a min. There is no need to have max speed in the kitchen .. Most or half of it goes to waste as the tap if left on just throws (expensive) hot water down the drain. A water Saving spray on the end of taps could also help. But I broke the first one I bought, never got round to buying another... I'll look into this again.

the shower I use myself I keep the hot water on max. Still at times I feel a weakness or inconvenience. I hope an improvement in boiler hot water speed will cure most of the problem..

The point you made about incoming water pressure and gas. Is a great one. Nice! I didn't think of this. I will check with a few professionals and see what they say is my limitation for the both the water supply and gas. I won't want to do too much extra work unless it's needed and makes 100% sense.

Thanks again! Awesome!

 

[Z. RANA]

4) the 28kw combi was doing well till now (except for hot water at some short times during the day). At only about 10 L/min. I can see why. An upgrade to 32kw = 13 L/min or better still 38kw = 16 L/min, I feel may do the trick.

If a 28 kW boiler gives 10L/min then I don't see how your 32 kW is going to give much more than about 11.5 li/min.

I have the si II model (it's not high efficiency only 80% efficient, rated D).

The Cdi model (this is high efficiency, about ~ 90.5% efficient, rated A ) gives more hot water output for the same power.

28 si II = 28kw = 10.3 L/min
28cdi = 28kw = 11.4 L/min
32cdi = 32kw = 13.1 L/min
36cdi = 36kw = 14.7 L/min
38cdi = 38kw = 16.4 L/min
42cdi = 42kw = 17.1 L/min

 

[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 28si II combi (about 80% efficient and D rated!) was doing well till now (except for hot water at some short times during the day). At only about 28kw ~ 10.3 L/min. I can see why.

An upgrade to 32cdi (90.5% efficient and A rated) = 32kw = 13.1 L/min or better still 38kw = 16.4 L/min, I feel may do the trick.

The si is a different model and different efficiency to the Cdi. I have the si II model but the Cdi at the same rating seems to give pound for better hot water flow rate.

 

[stardanny]

Unvented cylinder and system boiler is the better way.

Daniel.

 

[dilalio]

It's all down to your existing dynamic pressure and flow!
Otherwise you'll be looking at a new incoming main or accumulator.

 

[Dan Robinson]

And depending on other appliances, a bigger has meter and service pipe.

Turning down local service valves is the wrong way to control the flow.

https://www.bes.co.uk/product/99~PL~1768~Compression-CP961-FLOW-REGULATOR-BALL-VALVES.html

Fitting a second boiler in your home would be retarded. Becareful what advice you follow.