Boiler Size Advice

[Phillay]

Hey chaps,

Got to get a new boiler in, the one that's packed up is a Halstead Finest Combi (I know, I know, it's about as good as a chocolate teapot, but it was here when we purchased the house unfortunately).

We live in a 3 bed semi, 1 bathroom, downstairs toilet... so not huge (10 Rads). Boiler was previously in the attic, but is being moved to a cupboard at the top of the stairs so it's more central.

We'll mostly take showers, but I enjoy the odd bath now and then. We were looking at a W-Bosch Greenstar 25si Combi, as it gets great reviews, fits in the cupboard, efficient etc...

For £100 extra, we can pick up the exact same boiler, but 30kw instead of 25kw. Heating output's the same, well pretty much everything is other than the obvious slightly higher power consumption. The main attraction though is the increased flow rate from 8.9 to 10.7 l/p between the two models at 40 degrees.

My father in law who used to be on the tools (Gas Safe, the lot), reckons 30kw would be overkill... but I'd be interested to see what others think? Previous Halstead was somewhere between 25kw-30kw, but we have no manuals and I can't find much on the web!

Cheers!

 

[Destroyer2813]

Definitely go with the 30kw over the 25 for me if you get a recommended Worcester installer to fit it you wil get a longer warranty as wel Worcesters are all I fit and don't have any problems with them l, sure others will be along soon slating them

 

[jtsplumbing]

Go for the larger boiler, most combi's run 24K for heating the extra (6K) in this case kicks in to give you more hot water, Look at the Ariston range, with these you can adjust the output for the heating, wile still giving max power for hot water, Baxi doing 10 year warranty until June, ideal 7 years, Ariston 5 years, do some more research My self I won't fit Worcester's had to meny issues with them

 

[Killy Bing]

you size a combi on the hot water demand rather than the heating demand, which is likely to be less than 12kw for your house, by a fair bit if its a more recent house.

you might need a pipework upgrade on the gas to supply the new 30 kw boiler.
some pipework sizing would be needed.

if i was going for a combi i would go for atleast a 30 because i like my showers !!!

food for thought
an ideal logic plus 30kw boiler would be slightly cheaper and have another two years of warranty bringing it to 7

 

[Phillay]

Yeah, these both 24kw heating output jts.

The house was built in 1970 Killy, so not so much new... but we've got cavity wall insulation and the lofts well packed outside of the boarded areas.

Gas pipe's already 22mm, (which we've had calculated is right the size)... a plumber did suggest the Ideal Logic Plus to us, but he recommended the 24kw... until you guys today, I'm the only one who seemed to be going on about a 30kw one, just can't help thinking that for the extract ££s it's gonna be better in the long run.

 

[jtsplumbing]

You will be disappointed with hot water supply from a 24, not often I fit anything less than a 30, all depends on water demand.

 

[Phillay]

Cheers, that's my concern really... makes sense to me to over compensate if anything.

Last thing I want is the wife moaning at me because the bath is taking way too long to fill!

 

[IND_Nick]

Sizing a combi is generally all about flow rate, no point in a 30kw if you only have 9l/m. I would suggest you check the flow rate and size accordingly. Worcester boilers can have the central heating output adjusted to suit the property needs, as said previously most 3 bed semis only need 12kw to 15kw for Heating.

 

[Ermintrude]

I wouldn't install a 24Kw in most flats! but I'm sorry but all the advice you have had before you came on forum was nonsense. 28 / 30kw is the bare bones combi for almost all applications. just make sure you have the water flow. and as for worester - ideal much better choice for cupboard. go with a 35kw for less ££££ and better build quality, better performance, easier to service & repair!

:43:

 

[IDCHAPPY]

You will be disappointed with hot water supply from a 24, not often I fit anything less than a 30, all depends on water demand.

This^ 28-30 + Kw for a semi decent hot water supply

 

[Phillay]

Yeah, we've got the flow rate... can't remember exactly what reading I took, but it was more than enough... and that was taken at the furthest tap in the system.

Additionally, 4 bar pressure, so plenty for the old thermo shower. Just want to get the best hot water flow rate without going completely overkill on the size of the boiler you know... ain't too fussed about it trying to rival a stored hot system.

Bathrooms only 2.5 metres away from the cupboard where the boiler would be and the kitchen's directly below the bathroom... not much distance in legs of pipework!