35 kW heat output HE boiler on 22 mm heating circuits?

[Agile]

Has anyone experienced that senario in a house with a 32 kW radiator heat output at a 70° flow temperature?

Does a typical boiler like a vailliant 937 provide enough flow using its internal pump when its a 22 mm heating circuit?

Tony

 

[Deleted member 105431]

I would say it's borderline but a 937 has 28kw htg output I think.

 

[namsag]

Case of MI tony as some boilers say an additional pump has to be used over a certain output

 

[Agile]

Case of MI tony as some boilers say an additional pump has to be used over a certain output

Most seem to take the view that the internal pump is adequate but assume the external pipework is correctly sized with a low flow resistance.

This house is not only piped in 22 mm but also quite large so long runs of pipework are involved.

I would like a few more views on this problem as its the practical operation which counts.

Tony

 

[namsag]

What boiler and have you actually read the MI to see if it asks for 28mm or additional pump otherwise everyone is just guessing.
If you want the practical answer then its you on site who will have to check length of time rads take to warm up and whether it can all be balanced properly to achieve temp differential

 

[mehran]

i was told as a rule of thumb that 24kw is the most you should expect out of 22mm pipe under normal conditions. if you need more then you should upgrade to 28mm.

 

[simond]

If you haven't installed the pipework then the rule of thumb applies. What was the previous engine plant and how did that cope?

The 937 only has 28Kw CH anyway, and a two stage pump. We haven't had a scenario where the second outboard pump has been required and we have installed 20-30 of this model.

On a 637 (37Kw output) we have added the occasional pump via the Vaillant accessory PCB.

 

[Agile]

The boiler has not been chosen but is likely to be 35 kW heat only.

The existing system used a 15-60 and two boilers giving a total of about 40 kW at 80° C.

Only one of the boilers is working now ( and much of the past times too ).

To change to a lower flow of 70° more water flow will be needed than before.

I am really looking for installers who have fitted 35 kW boilers to systems with about 32 kW of rads and only a 22 mm feed !

As mehran says the rule of thumb is 24 kW max for 22 mm.

Any more comments? I thought installers met this often.

Tony

 

[Deleted member 105431]

I would make two quotes;-

1) use existing (and possibly undersized pipework)
2) quote to upgrade primaries to 28mm and/or fit an additional pump. Advise customer of the situation and see if they are willing to pay the extra.

 

[muggles]

Glowworm Ultracom 38hxi heat-only boiler has a quoted 38kw output on 22mm flow and returns, with no requirement that I can find for upgrading to 28mm.

http://www.glow-worm.co.uk/products/pdf/current/ultracom_specifications.pdf

http://www.glow-worm.co.uk/products/pdf/current/Ultracom_hxi_installation_manual.pdf

 

[doitall]

Simple Tony.

A heat only has a remote pump, so use a 15/60 or 25/55.

Alternatively make a low loss header and use a shunt pump to circulate around the boiler + a 15/60 for the system

 

[Agile]

I have got to check if I get the job but I think there may be a possibility of replacing in 28 mm up to the point where it splits to go upstairs and downstairs.

If not then a more powerful pump seems to be the other possibility although this is a price concious cust and the larger pumps are quite a high price!

Tony

 

[gas4you]

I've always gone to 28mm for anything over 18Kw. I have only ever fitted 30Kw plus onto 28mm minimum sized pipes from boiler to zone valves.

 

[doitall]

Don't think price is an option Tony.

They either want it to work at all cost or they can't afford it.

In which case you walk away, because it will be your fault if it doesn't.

 

[Deleted member 105431]

Don't think price is an option Tony.

They either want it to work at all cost or they can't afford it.

In which case you walk away, because it will be your fault if it doesn't.

very true indeed.