help with boiler sizing

[newbuildinstaller]

Hi iv been a gas safe installer for 2 years.
I have always worked for a large contractor so never had to size system before and it was never really covered in college either.

I have recently started my own company and was wondering how to best size systems (boiler kW) I know you can just fling in any huge boiler and that will do but what is the best way to do this properly as im sure that way cant be cost effective.

Im sizing a barn conversion with a 250litre cylinder (3 en-suites 1 bathroom). Its on 2 zones and has 20 rads? I was going to just put in a Greenstar 40CDI regular.

Im sure that will be big enough or any ideas?

 

[D_Hailsham]

Im sizing a barn conversion with a 250litre cylinder (3 en-suites 1 bathroom). Its on 2 zones and has 20 rads? I was going to just put in a Greenstar 40CDI regular. Im sure that will be big enough or any ideas?

Is this a completely new installation (boiler and rads) or just a new boiler on an existing installation?

If it's a new installation, you should be able to find out the design heat loss from the architects - the conversion will have to comply with current building regulations.

If just a new boiler, you should find out the output of the existing rads. Use Stelrad Elite Catalogue if they are standard steel rads.

You can also use the Boiler Size Calculator

Have you considered weather compensation?

 

[ianniann]

Fingers crossed the radiator sizes match up to the heat loss figures or the biggest boiler in the world won't cut it

 

[newbuildinstaller]

thats the thing the architects drawing shows a combi boiler!?!?!?! I said that wouldn't work and that a unvented was the way to go! the drawings also show no radiators no drains! New system by the way.

 

[D_Hailsham]

thats the thing the architects drawing shows a combi boiler!?!?!?! I said that wouldn't work and that a unvented was the way to go! the drawings also show no radiators no drains! New system by the way.

Sack the architect! That's assuming (s)he is an architect and not just a drawing technician. In any case the drawings etc should show the heat-loss calculations, which can be used to size the boiler.

How far along is the build/conversion? Have any of the heating pipes been installed? Is it too late to consider underfloor heating?

With four bathrooms/showers a combi will never cope, unless the water flow rate and pressure are really high; and I bet the "architect" never checked that before specifying a combi.

 

[Whitespirit66]

Here's some bed time reading for you. Have found this book very useful myself.

http://www.hvcapublications.co.uk/Ecommerce/ID/68/Product/DomesticHeatingDesignGuide/Details.aspx

 

[newbuildinstaller]

The build hasn't started yet underfloor heatings a good idea. Even considered offering solar for the hot water. I never realised how spoilt I was working for a big contractor we used to get full plans with radiator sizes and even pipe sizes with pipe runs shown

 

[D_Hailsham]

The build hasn't started yet

You're in an envious position. No need to compromise as everything can be designed from the ground up.

Do the architects drawing have heat loss info for all rooms?

Underfloor - yes; solar - possibly, depends on where the barn is located, planning permission etc and the client's budget.

If the client insists on radiators, don't forget to oversize them so the boiler can run at lower temperatures and condense more often.

Knowing the size of most barns, the system will have to be zoned with separate time and temperature controls for each zone.

I never realised how spoilt I was working for a big contractor we used to get full plans with radiator sizes and even pipe sizes with pipe runs shown

You mean they did the job properly.

Reminds me of when I spent part of my school holidays in the drawing office of a large firm of M&E contractors in London putting all the cable runs, light fittings etc on to the architects' drawings for an office block.