What size boiler

Joined
5 Oct 2008
Messages
210
Reaction score
0
Location
Bournemouth
Country
United Kingdom
What size boiler would you recommend for a 3 bed semi - with hot water cylinder, standard size? I'd like to get a heat only ideally instead of having a combi. Have open vented system at the moment and have heard converting to sealed can cause problems with leaks.

Any recommendations please would be great.
 
Sponsored Links
Heatloss calcs are required but probably 18kw is a starting point.Take your installers advice on boiler makes.Sealed systems are better,but pressurising an older system will find weaknesses.If any of your CH piping is under concrete floors be aware that if it leaks then it could be a repipe.
 
Thanks - I was being told that having a bigger boiler than needed is best as the boiler won't be working flat out and in future any add ons etc can be catered for.

18kw seems small I feel
 
There are combis with high flowrates by top makers that will more than do a semi providing the main water can handle the water rate and pressure. So do not dismiss these. These tend to have high kW ratings such as, 35kW and above. They modulate down so, not a problem and built in expansion if extending in the future.

If the existing vented pipework leaks then it is dodgy anyhow, so better fix now than later. Make sure the old rads and pipes are cleaned out.

Look at the current thread on the Intergas and ATAG. The Integas is a very reliable combi. I have fitted a few and most feedback is that they just go and go. I have never been back to one.
 
Sponsored Links
What size boiler would you recommend for a 3 bed semi - with hot water cylinder, standard size? I'd like to get a heat only ideally instead of having a combi. Have open vented system at the moment and have heard converting to sealed can cause problems with leaks.
Use the Boiler Size Calculator to find what size boiler you need; I doubt if you need an 18kW for a 3-bed semi. Although, if you have plans to enlarge the house or have very poor insulation, you may need something about that size.

The argument that a large boiler will be better because it won't be working flat out is fallacious: it's not like a car engine! In any case the number of days a boiler is producing max output is relatively few.
 
Thanks - I was being told that having a bigger boiler than needed is best as the boiler won't be working flat out and in future any add ons etc can be catered for.

18kw seems small I feel

Which idiot told you that?

Most reasonably well insulated semis only need 15 kW boilers!

Why do feel that an oversized 18 kW is too small?

Tony
 
18kw seems small I feel
I suggested 18 kw as a starting point,but calcs may well indicate only 12/15 kw.As Mr Hailsham suggested do calcs and make allowances for future alterations eg maybe another couple of rads in an extension/conservatory.Do not over engineer boiler output.
 
The Integas is a very reliable combi. I have fitted a few and most feedback is that they just go and go. I have never been back to one.

LOL you are hilarious. Yes, have a look at the other thread where George DRivel Burner is asking basic questions about a boiler he has apparently installed. If you'd fitted one you'd at least know what pump was in it !
 
The Integas is a very reliable combi. I have fitted a few and most feedback is that they just go and go. I have never been back to one.

LOL you are hilarious. Yes, have a look at the other thread where George DRivel Burner is asking basic questions about a boiler he has apparently installed. If you'd fitted one you'd at least know what pump was in it !

I don't know about the other thread. This forum has em indeed. The Intergas has a standard pump. Do you know what that is?
 
The Integas is a very reliable combi. I have fitted a few and most feedback is that they just go and go. I have never been back to one.

LOL you are hilarious. Yes, have a look at the other thread where George DRivel Burner is asking basic questions about a boiler he has apparently installed. If you'd fitted one you'd at least know what pump was in it !

I don't know about the other thread. This forum has em indeed. The Intergas has a standard pump. Do you know what that is?

I think he meant what make of pump ;)
 
Thanks - I was being told that having a bigger boiler than needed is best as the boiler won't be working flat out and in future any add ons etc can be catered for.

18kw seems small I feel

It is really simple.
The boiler system can not dissipate more heat than the total of rads are capable off.
Therefore, the heatloss calculation method as promoted by mr Hailsham ( who is not heating pro, but our resident google hero ) is totally useless.
Measure up the length or your rads. Add all the lengths together, whilst correcting to a height of 600 mm ( e.g. 1200 x 500 becomes 1000 x 600 ).
1 metre length equals 1 kW output, e.g. 14 metres will require a boiler of 14 kW. Now add any possible future upgrades and additions to the number you found.
This is the size you need. Forget the theoretical calculation outcome, unless you are prepared to replace all your radiators to match the calculated outcome.
If you replace your old timer for a modern independent 2-channel model, you will have a much better performance of both CH and DHW, and no need to add capacity for DHW production as it will be done when the CH is not on.
 
Of course double radiators are different, finned radiators are different, fanned radiators are different, and the output varies quite dramatically with temperature. So measuring your radiators is just as useless as calculating the heating needs of your house :)

So do both. Use the smallest of the two to size your boiler (note that if your radiators aren't enough to heat your house, you may need to run the system very hot in winter, get some more radiators, get some more insulation, or just wear a coat when it is very cold outside). Both methods are approximate, and a few kW bigger is no problem. Double would be a problem. You can often downrate modern boilers but then you're paying for a whole lot of something you aren't using (unless you needed a big powerful combi for hot water).
 
sizing a boiler to match possible undersized rads is quite literally the stupidest thing I have ever heard.

size the boiler for the heatloss of the house plus any extra you think you may need for hot water or any future extension.

also find a boiler that has a good modulation range that can meet your needs.

for example if the heatloss comes out at 15kw then a boiler that can go from 4kw-30kw is better then one that can only range of 9-16kw...
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top