boiler to radiator ratio

[fionaoutdoors]

i have a Vikera Excell 80 PS combi boiler. we're about to have an extension built and we're hopig we will not have to replace the bolier for a bigger model. can anyone tell us approximately how many radiators the 80 PS can run. or is it done on floor area of the whole house?

 

[croydoncorgi]

No - it's done according to the heat-loss for the whole house.
Relatively simple to work out, based on construction, room size, external / internal walls, glazing type, insulation,.....

But in the real world....
Unless the house is very large already and / or the boiler is on its Last Legs, given that it's a combi it's probably easily big enough to run an extra rad or two. I'd be more concerned about the sizing of the pipework....

 

[fionaoutdoors]

oh my... sizing of the pipework?! what does this mean?

 

[croydoncorgi]

The pipework which supplies your new rads must be large enough. As a rule of thumb, 15mm can only supply up to 2 large rads or 3 small ones. Above that (in a domestic setup) you need to go to 22mm pipes. Not clear yet what new connections will need to be made in your situation.

 

[nickso]

croydon is correct in what he has said but why dont you just wait and see what happens? unless your house is already large and stretching the boilers capabilities then its unlikely to need upgrading.

do be aware of what size of pipe the installer uses on the extension. all too often they use microbore pipe for massive runs and then tee it into another rad to make matters even worse.

 

[kevindgas]

as a rule of thumb calculation i allow 5,000 btu per rad (some will be more some less) and it usually works ok above 12 rads the pump may struggle but you can add another pump some where else in the system just make sure it has a common electric supply with the 1 in the boiler.