Combi Boiler Size advice

[Johnb1977]

I'm looking to have a Combi Boiler installed along with 8 Radiators in each room along with a Towel rail in the bathroom.

I wanted to check with people what size combi boiler people think I need as I have had one company who has quoted me for a Worcester green star 28cdi compact boiler and have had another company quote me for a Worcester 30I Greenstar Condensing Combination Boiler.

I've listed below the size of radiators I am going to have, any help and advice that anyone can give me would be greatly appreciated.

• Hall (1000mm x 600mm double radiator)
• Kitchen (800mm x 600mm double radiator)
• Down stairs toilet (400mm 500mm single radiator)
• Back room (1000mm x 600mm single radiator)
• Front living room (1000mm x 600mm single radiator)
• Front Bedroom (1000mm x 500mm single radiator)
• Back Bedroom (1000mm x 500mm single radiator)
• Box Room (600mm x 500mm single radiator)
• Bathroom (1600x600mm Towel Rail radiator)

 

[Scott_D]

How many hot water outlets?
What’s your main cold water flow rate?

 

[Old Account]

How many bathrooms have you got? And as Scott has already asked above what’s your mains incoming pressure and flowrate

 

[Johnb1977]

Hot water outlets will be Kitchen sink, downstairs toilet wash basin, bathroom bath and wash basin. I'm not sure about the flow rate I do know that the water pressure is very high.

 

[Old Account]

Seems like the 28 is well enough.

 

[Chalked]

Even the smallest combi will do your radiators.
The higher the output, the higher your hot water flow rate.
This will need your water pressure and flow rate checked.

 

[Aire]

Combis are sized mainly on the hot water demand instead of heating requirements. Both Worcesters quoted will do the job, they're both rated at 24kw for heating output which is more than enough. The difference is the 30i delivers 30kw for hot water instead of 28kw delivered by the 28cdi.

Personally I wouldn't go with either though and instead i'd recommend the baxi 630. 7 year guarantee, cheaper than the worcester, still delivers 30kw of hot water with flow rates matching that of the 30kw Worcester, but only delivers 20kw on the heating side, which is still more than enough but obviously less wasted energy.

But as others have said, get your flow rates check to make sure your system is suitable to run a combi before you decide which boiler to go for.

 

[Riley]

Most modern boilers can be range rated down in order to cope with your heating requirements efficiently. I also would not pick the Worcester’s.