HI
I am thinking of changing my Combi boiler as its old and a bit unreliable.
I have seen some offers in the local plumber merchants and wondering how one works out what size of boiler is required. By Size i mean the capacity in KW
Is there somewhere (website) where you can work this out. I guess its based on no of rads and bathrooms etc.
Thanks
Bhupesh
Not really. The main consideration with a combi is how fast it can heat your hot water - so that it doesn't take all day to run a bath.
Get that right, and you'll have more than enough capacity for your radiators - unless you live in Buck House!
In terms of hot water production, the best thing is to go for the largest that you can get. However two caveats:
- Gas supply must be adequate all the way back to the meter. This usually means at least 22mm pipework for the whole length.
- Some of the larger boilers are quite physically large so check the size.
- You can't determine the CH requirement by counting the number of radiators. They vary in size too much. However, if you go for a large combi, it doesn't matter because it will reduce its heat output when warming the radiators. Usually heat requirement for hot water is much greater than for room heating.
What have you got now? Other than the unreliability, does it meet your requirements for hot water provision and heating?
Take a read of the Boiler Choice FAQ.
Hi
Thanks for the replies
I currently have a Vokera EXcel 80 SP, thats what written on the box, but I dont know any more about it. heating is fine but getting DHW is a real pain. When you turn the hot tap on the boiler fires and give hot water for about 5 mins, then the boler shuts down for 5 mins, giving cold water. Then it starts up again.
I have had a few engineers look at it, but I dont really want to spend any more money on it. Its over 10years old according to the people that look at it. It was present when I purchased the house 2 years ago.
I have seen a 28KW Valiant for 700 (+ VAT), and thought that ir would be OK for me. I live in a 3 bed house, one bath, no shower, 7 rads
Is 28KW OK
Thanks
Bhupesh
The Vokera one is 23kW.
Are you happy with its hot water output? If you are then the Vaillant will do more. If you are not, it needs to be researched more and perhaps you need something larger.
As has been said, the radiator count says nothing about the CH requirements. Again though, if it has been OK with the Vokera in the past it will be with the Vaillant.
Did you check physical sizing of the box and the gas supply?
HI Andy
THanks forthe info on the Vokera. 23KW sounds quite low as most now start at 24KW and they are recommended for smaller properties (flats etc).
The hot water is really poor at the moment as I have described, so I am hoping that will get better with a new one. Heating is very good. I have actually reduced the number of radiators in the house as well.
I have not checked the size of the boiler, but I am moving the location (from upstairs to downstairs), and I have a blank wall to put in on so I hope there will not be any problem in that area. The vokera is actually quite big. I am sure the new ones are more compact.
Not checked the gas supply, but since I am moving location, that will have to be redone almost certainly.
Bhupesh
Andy Hall wrote:
In general the peak demand for hot water easily exceeds the background demand for heating in MOST houses.
So, with combis, sizing for hot water s generally good enough.
A very dirty rule of thumb for heating is that you should allow
50W/square meter TOTAL floor area in a well insulated house, 100W in an average one, and 200W in a rather poor one.This is by no means accurate, but helps get the 'feel' of the requirements.
OT aside... =========== If you note that the winter average solar energy can be down to as little as 40W/sq meter for a surface, you can see why even covering the entire roof of a two storey property with solar panels (netting you
20W/sq meter at enormous cost), makes bugger all difference to heating bills..
You mean that that salesman with the dripping gold isn't telling me the truth again?
I suspect that the current boiler is much below 23kw effective HW heating due to. Limescale build up and/or diverter valve let by and/or water flow diapragm problems. etc.
The Vaillant 28kW will be a good choice (the 24kw still pretty good). Do check that the gas pipes are up to the job fr the 28kW version.
Don't get me going. My doddery 88 year old F.I.L. has just signed up to spend 30% of all the capital he has left (£4800 I think the bill was) to save '50% of all his heating bills, except the aga sir'
I pointed out to him that the combination of panels he had selected would produce at the most optimistic using the figures in the brochure £200 a year saving, if they were 100% efficient and he could in fact make use of *all* the summer sun.
His oil bill is around £2000 a year at current rates..of which perhaps
30% is the aga at most..He assures me that all the people they gave as referees assured him that the kit was stunningly wonderful, best thing they had ever bought, etc etc.
But he is panicking about his oil bills and reason has gone out of the window.
That's a dirty trick to pull on someone in that position. Can you help him to undo it?
I suppose that there are no other conventional fuels that could be accessible to him?
I can see why you would want to hang a greenie. By the bollocks. The massively overoptimistic claims have paved the way for charlatans.
Not if he chooses to believe the salesmen and their shills, instead of me ;-(
Plenty of wood in the shed..
Actually the whole house needs a complete draught and insulation overhaul. That would be more cost effective.
This isn't greeny, this is plain climbing on the oil price bandwagon and using classic FUD to sell crap.
Oh dear. The trouble is that by the time he figures this out, it will be way too late to do something to the company.
Unwittingly, or perhaps wittingly, the greenies are providing the marketing without cost and ROI factored in.
It's safe to assume, NP, you being the son-in-law in question, that he has got all his free-for-the-over-70s insulation installed by now? (cavity wall, 1000mm in the loft (whatever the latest "standard" is (it's changed four times I think, since I first started putting in loft insulation!))
john
p.s I should add also: a friend of mine discovered that his mother was entitled to god-knows-what (new CH system?!) free from "the council" as long as she was in receipt of *any benefit whatsoever*. I think they discovered she was getting about a fiver a month for some reason or other, and the floodgates opened...
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