Two boilers,30 rads on 2" and a low loss header.

[Kbgas]

Hi

can any one give any advise on the best way to fit a low loss header and if i actually need one.
I have 30 rads and a 250l unvented cylinder.The heating flow and return in the boiler room are 2" steel.
Im looking at fitting 2 30kw system boilers with a low loss header,a 40/80 grundfos pump on the secondary loop.

The Question

can the HW be fitted on the primary loop?
Whats the best solution?
Do i need to get a 2" zone valve £££££££ or can i down size just before the header.

Thanks in advance.

KB

 

[Cds]

Would it not bebetter to fit 2 or 3 take offs from the header rather than 1 big one. I wouldnormally design these to have a takeoff to each heating zone and one to the DHWand possibly one to a towel rail circuit.

The pipework isthen 28 mm or 22 mm and although you now need 3 or 4 pumps these are allsmaller (15-50/60) which usually works out cheaper.

 

[Roger Welton]

I agree with cds

 

[Phil B]

Also agree

 

[hammers4spanner]

i concur

 

[tamz]

I also agree but if it is an existing set up it may be awkward and expensive to alter. Try to take as many connections from the header as you can

If the HW circuit is there separate, take it off the header with its own pump.
You shouldn't need zone valves if you can split the flows to separate connections.
Most manus have a bit about cascading boilers these days. If they don't you will find a bit on the worcester, vaillant and keston websites and also most commercial boiler manus like remeha.

Make sure you size the header correctly. You can work it out using the formula. (always round up to a pipe size)

Diameter of header (mm) = ( √((flow rate in m³/s x 1.28 )/ design flow velocity through the header) x 1000)
If you use 0.5 as the design flow velocity you are sizing for worst case.

You can get the flow rate by using this formula
flow rate in m³/s = kw / (4.186 x delta t ) /1000