Kw of system boilers

[Scott_D]

10 rad system and 210l unvented with a 16kw coil
Do you size to cope with full heating load and full coil kw which may be needed in a rare occasion (25-28kw)
Or size for usual demand (15-18kw)

I tend to go for the bigger value as there is less chance you will get a call but it’s going to cycle more as it won’t modulate down as low.

 

[mfgs]

For something like that you can’t really justify sizing for full coil kw unless there is massive hot water demand. I would be looking at approx 18kw and advise to time the hot water to come on at different time to the heating.

 

[Chalked]

An overworked small condensing boiler is more efficient than an oversized.

 

[ShaunCorbs]

I would size it at 18kw and stagger the hot water times you will find it will take around 40-55 mins to heat up the cylinder from cold

 

[king of pipes]

Depends on the property a well insulated thermally efficient home you can go with a lower kw boiler, traditionally brick and block built I find you need the extra to get you to a comfortable temperature quicker I'd go larger, on Valliant system boilers you can alter the cycling time and down rate the kw so not really a issue . Kop

 

[Scott_D]

I’m also tempted to go for a combi used as a system, the price of system boilers is much higher at the moment.

 

[king of pipes]

Why not I've done it feed the kitchen sink off it or utility maybe