KW boiler ratings

[Jonmyates]

Hello all.

We've been advised that if we were to have a combi we'd need a 38kw (wb cdi)

We're now looking at a heat only boiler and have noticed that a lot of the manufactures don't make a heat only boiler over 30kw. At least wb and ideal don't seem too.

Does this mean that a less kw boiler is needed when using a heat only boiler to a combi? Or regardless of boiler type, we'll always need the same kw?

thanks all.

Jon

 

[Ray Stafford]

Hi Jon

Most combis are working well within their limits when they are in heating mode.

The better ones have high rated burners to boost the instant hot-water output. For almost all domestic applications, installers will therefore size a combi based on the hot water demand, confident in the knowledge that there will be output to spare on the heating side.

If you are going to switch plan to a heat only boiler, you will probably* be able to get away with a lower output boiler, since it will be calculated based on your space heating requirements, rather than the hot water requirements.


* depending on the size and construction of the property.

 

[TBServices]

If you need a 38kw boiler to heat your home, you shouldn't be having a combi installed. Combi boilers are usually sized based upon their hot water performance, not the CH requirement of the house.

Leave boiler sizing to the professionals, and if you're not sure about your professional, change him.

How large is your home? How many rads and bathrooms?

 

[jefaz]

A 38kw combi means only the hot water will deliver an output of 38kw and the heating use a lower kw.
In this instance the output for hot water is 40kw and for heating it's 9.4-30kw
If you go for a heat only boiler there is no need for it to heat hot water directly and so needs a lower rating

 

[Jonmyates]

All. Thank you.

The property is a 1969 detached 4 bed. 8 rads and 3 towel rails.

2 bathrooms and a WC.

Would a 30kw heat only suffice?

regards.

Jon

 

[Ray Stafford]

Hi Jon

There are too many variables to calculate via an internet forum. As TBServices says above - leave it to your installer to size it. There are some online calculators on the web, but to be honest, I am a bit dubious about some of them. Since it can be an expensive thing to get wrong - why not leave it to the professional?

Ray

 

[TBServices]

All. Thank you.

The property is a 1969 detached 4 bed. 8 rads and 3 towel rails.

2 bathrooms and a WC.

Would a 30kw heat only suffice?

regards.

Jon

It's likely that you won't need a 30kw heat only boiler, but as ray suggested, the only person who can accurately say that is a trained professional who's sized up your home. I would suggest however that with 2 bathrooms, you think of a hot water source other than a combi, possibly an unvented cylinder, but again, there are lots of variables.

You really don't need to concern yourself with boiler sizing.

 

[Deleted member 32524]

try the plumbcentre heatloss calculator. this will let you know what size for the heating. hw look at flow rates of boiler. combi boilers are not a solution for every house.

if for example two hot taps being used at same time would result in poor flow through them if you only look at CH needs. you can get high flow ones but expensive. (wb)

 

[Howsie]

Where are you based?