central Heating Pump Size

[agsaunders]

Hi, I recently moved house and had a new 40kw Bosch condensing Boiler fitted and the system flushed but the two furthest radiators in the system dont seem to give out enough heat or as much as all the others.( our living room)

There are 20 double convectors and 3 heated towel rails.

Pipe work is 22mm with 15mm to radiators.

Tried balancing the system and feel I either need to fit a couple of higher output radiators or a better circ pump ( room is approx 38m2), current ones are approx 1800 watts each with a delta T of 50 deg C.
Circ pump is a British Gas Multhead G. Radiators outer temp is approx 59 to 62 deg C. TRVs are fitted on all except three radiators.

I am considering high output aluminium radiators.

Any suggestions most welcome. House is cavity wall insulated, suspended wooden floors with UPVC double glazing throughout.Built in 1988.

many thanks

Andy

 

[D_Hailsham]

had a new 40kw Bosch condensing Presumably the 40CDi Classic Regular.

There are 20 double convectors and 3 heated towel rails.

So that will be about 30-32kW max. Why such a large boiler? Was it sized using the Whole House Boiler Size Calculator?

Pipe work is 22mm with 15mm to radiators.

delta T of 50 deg C.

Presumably difference between rad mean temp and air temp. What temp drop are you aiming for across the rad - flow to return? What is the drop across the boiler?

Radiators outer temp is approx 59 to 62 deg C.

What is the boiler flow temp?

I am considering high output aluminium radiators.

There's very little difference in outputs between steel and aluminium rads of the same size and type.

 

[agsaunders]

had a new 40kw Bosch condensing Presumably the 40CDi Classic Regular.

Thanks for the speedy response.

Yes a 40 cdi regular, previously a ferolli Sigma 30kw i believe , heat exchanger choked up and high CO emissions, would you believe recently serviced by BG.?

There are 20 double convectors and 3 heated towel rails.

So that will be about 30-32kW max. Why such a large boiler? Was it sized using the Whole House Boiler Size Calculator?

it recommended 32 kw, the price difference was not a lot and i was considering underflloor heating for 60m2 in the future.

Pipe work is 22mm with 15mm to radiators.

delta T of 50 deg C.

Presumably difference between rad mean temp and air temp. What temp drop are you aiming for across the rad - flow to return? What is the drop across the boiler?

12 deg as i understand this is the optimum for a radiator when balancing system. Worst radiator is 52 in 32 out, all the others are fine. the 50 deg C was quoted as the ideal for the current radiators, i estimate a minimum of 3600 watts for the room in question, from mysons brochure with a temp diff of 45 Deg C i would require 4137 watts for a comparable radiator.

Radiators outer temp is approx 59 to 62 deg C.

What is the boiler flow temp?
boiler temp is 73deg c

I am considering high output aluminium radiators.

There's very little difference in outputs between steel and aluminium rads of the same size and type.

thats good to hear as they are expensive, the ones i had in mind are a direct replacement pipe centre wise and give a 500w greater output than the current Myson round tops.

 

[Andygasman2010]

22mm pipework from a 40kw boiler is undersized, you need to fit a Grundfos 25/80.

 

[CBF]

22mm pipework from a 40kw boiler is undersized, you need to fit a Grundfos 25/80.

don't let Lee see this

 

[Dan Robinson]

 

[Andygasman2010]

Ha Why? For or against?!

 

[xr4x4]

Need the boiler model but 22mm is recommended on other 40kw Bosch boilers.

 

[dcawkwell]

You can try balancing the system and if you have thermostatic valves
on and the rooms actually get to temperature so the thermostatic valve
shuts off it will work as once a room gets hot the water will diverted to other rooms. (note this won't work if you have thermostatic valves set at 5 as the rooms will never get to that temperature)

If you need all the radiators on at once you will need more than one pump.
You can balance about 13-15 radiators usually more and it needs a bigger pump or multiple pumps. I would suggest more than one pump.
One for upstairs another for downstairs.

 

[Andygasman2010]

Worcester recommend 22mm on some of their 40kw boilers? Or do you mean that they recommend 22mm minimum?

 

[xr4x4]

Looked at the 40 cdi? I think, said min of 22mm but the outlet connections on the boiler are 22mm on this model.

 

[agsaunders]

Need the boiler model but 22mm is recommended on other 40kw Bosch boilers.

its a 40 cdi greenstar regular

 

[agsaunders]

You can try balancing the system and if you have thermostatic valves
on and the rooms actually get to temperature so the thermostatic valve
shuts off it will work as once a room gets hot the water will diverted to other rooms. (note this won't work if you have thermostatic valves set at 5 as the rooms will never get to that temperature)

If you need all the radiators on at once you will need more than one pump.
You can balance about 13-15 radiators usually more and it needs a bigger pump or multiple pumps. I would suggest more than one pump.
One for upstairs another for downstairs.

Actually fitted Danfoss living eco to three rooms for the kids, work really well.I considered zoning but didnt fancy ripping the house apart to do it.
Dont need all the radiators on at once really and the others are set at three and are ok. It has a British gas Multihead G on , recently replaced but i cant tell you what it replaced. a Grundfos 25-30 has been recommended. Any thoughts on a more suitable pump ?

 

[dcawkwell]

You can try balancing the system and if you have thermostatic valves
on and the rooms actually get to temperature so the thermostatic valve
shuts off it will work as once a room gets hot the water will diverted to other rooms. (note this won't work if you have thermostatic valves set at 5 as the rooms will never get to that temperature)

If you need all the radiators on at once you will need more than one pump.
You can balance about 13-15 radiators usually more and it needs a bigger pump or multiple pumps. I would suggest more than one pump.
One for upstairs another for downstairs.

Actually fitted Danfoss living eco to three rooms for the kids, work really well.I considered zoning but didnt fancy ripping the house apart to do it.
Dont need all the radiators on at once really and the others are set at three and are ok. It has a British gas Multihead G on , recently replaced but i cant tell you what it replaced. a Grundfos 25-30 has been recommended. Any thoughts on a more suitable pump ?

Cheap £35 pump from screwfix will sort it. One circulating for upstairs
one for downstairs. Half day say to pipe in. Shouldn't be difficult.
Or zone them upstairs and downstairs.

 

[Andygasman2010]

Looked at the 40 cdi? I think, said min of 22mm but the outlet connections on the boiler are 22mm on this model.

This is mostly irrelevant, all depends on the system size.