Boiler size question

[g60rge]

Looking to swap out an old potterton on Promax 30 kW wall hung boiler at a mates house

he wants a vaillant, I suggested we get a like for like 30kw if all is working fine but noticed all pipe work to the boiler is 28mm

vaillant connections are 22mm, would i go up a size to the 438 to counter act this or will reducing near the boiler be sufficient?

I was thinking the potterton having 28mm pipes and connections helped it cope with so many rads
its a 20 rad system

 

[Dotty]

Moved off open forum

 

[Scott_D]

Upsize to 28mm as close to the boiler as possible
22mm will only carry 24kw IIRC

 

[g60rge]

I've been told that with new boilers they modulate down and will keep shutting down as it will keep circulating the closest rads

He said fit a low loss header or even zone off upstairs

My mate who is a Vaillant engineer said stick with a 430 as its upto the job

 

[mfgs]

Does the existing set up work? If so then a like for like boiler swap will be fine. Most boilers have 22mm connections now so just reduce down as close as possible to the boiler.
If the existing set up isn't working, then think about altering it.

 

[g60rge]

Makes sense

 

[PhoenixServices]

Should really be working out whole house heat loss the putting in the correct size boiler. Or at the very least range rating to the correct output. If he is thinking of ever having an extension put in a larger boiler than needed and range rating it.

 

[Masood]

Should really be working out whole house heat loss the putting in the correct size boiler. Or at the very least range rating to the correct output. If he is thinking of ever having an extension put in a larger boiler than needed and range rating it.

Definitely the right approach. Doesn't take that long to work out heat loss (loads of online calculators if you don't want to do it manually), and it may make a big difference in his bills...

 

[g60rge]

heat loss calculator doesn't take into account how many rads are currently in the house though, if there are 20 rads and the calculator tells me i need 20kw, there will be a few stone cold rads right?

unhappy customer...

 

[ShaunCorbs]

heat loss calculator doesn't take into account how many rads are currently in the house though, if there are 20 rads and the calculator tells me i need 20kw, there will be a few stone cold rads right?

unhappy customer...

heat loss the rooms and theres your kw then add 5kw for you cylinder

 

[PlumbersMate]

When calculating size of a combi what KW do you allow for HW?

 

[PhoenixServices]

You don't with a combi. The size of the combi is based on the required flow rates and hot water performance.