Boiler Capacity

DaveMc

I was considering adding a new radiator to my existing boiler system. Could someone advise if I have the calculations approximately correct?

Current Radiator output is 33k btu = 9.7 kW (5 Radiators)
Add 20% for Hot water = 11.6 kW
Add 10% for Loss in transport = 12.8 kW

The combi boiler output is between 9 and 24kW so I'm thinking I have plenty of room to expand the system?

Main reason I ask is that I had a plumber come round recently and tell me my boiler isn't rated to even supply the current system as is. :eek: He recommended replacing the boiler.

After checking myself (I find it hard to trust any tradesman ) I'm thinking he doesn't know the difference between btu and watts?

Are my calculations wrong? Seems a bit suspect that a boiler can't even supply 5 radiators (which is why I checked in the first place).

gas4you

Ignore your so called plumber. He is obviously out to get a new boiler install:mad:

You could double your system nearly and still be ok.

Combi's are always sized for HW output and therefore usually way overpowered for the ch side.

Canucklehead

Hi

If you look in the installation manual it will give you the output into C/H.
If you can't find the manual come back with the make and model.
I think you have more than enough output for more rads., but the manual will prove it.

Punting for work I suspect.

EDIT
Just like gas 4 you says

GSR.

ormus

if its a 24kw model then you probably could run a mansion in weybridge with it.
the plumber is talking boll ocks.

DaveMc

Thanks for the replies, its easy to doubt yourself when a professional tells you otherwise.

The installation manual gives two figures for Heat Output

23.8kW and 9.7kW

There are also two for Heat Input

25.8kW and 11.5kW

gas4you

The 2 heat output figures are maximum and minimum.

The minimum applies when the boiler has modulated down when the heat output required is not so great. That, for example, will be when all your rads are hot to touch, or some have turned off if you have TRV's fitted.

It will usually only use maximum output for a few minutes first thing in the morning when all rads are cold.

The heat input figures are for us to work out things like gas pipe sizing and ventilation if needed etc.

DaveMc

Thanks gas4you.

To be honest I don't think the plumber was trying it on... I think he just didn't know which is a bit scary (this is based on what I know about the person). I certainly hope thats the case anyway.

It did appear that he was using the btu amount against the kW output, which at the time I went along with (since I didn't know any better), but I rectified that situation when calucating my own btu figure and comming across a btu/watts chart and thinking wait a minute this is b*ll*cks. I also found it difficult to believe that a modern boiler couldn't supply 5 average radiators.

gas4you

Btu's = KW's x 3412