which size pump should i have

[goateater]

hi all new here
just changing a few of my old radiators, and was reading up about balancing system as for last few years had some radiators that i cannot get hot enough, but they are in 1 room so we rearely use it in winter
anyway one of the things i read about was that the temperture different between the boiler feed and return should be 11c tested my and its around 18c turned pump speed up to 3 which made a little change
so i'm wondering if pump is up to job
pump is a wilo gold star
i have 15 radiators
oil boiler 140000
and a wood burning store

do u thing the pump is ok
if not what should i look to get
i can't find and sites that say if you have 15 radiators you need this or that pump

 

[Axel]

I have 13 rads on a 30kw gas boiler and my Grungefoss 15-60 does the job well on speed setting 2. On 3 it's noisy in most of the rads.

 

[Biggles..]

Basically if you need all 44 kw which I'd be surprised then your pump need to shift

44/(4.2x11)= Lps

Lps x 3.6 = m3hr

Use grundfos's website to size your pump based on that flow rate and your head of water.

Suspect it will be far too large compared to what you actually need

 

[goateater]

thanks for the replys
will try thr grundfo's site

from may to september normally only have oil boiler running hot water, with odd cold days having heating on
rest of year have heating on but this one room never gets warm, tried balancing but never seem to get enough heat in pipes to these last radiators

 

[D_Hailsham]

I read ... that the temperature different between the boiler feed and return should be 11c.
...
oil boiler 140000

Older boilers were designed for an 11C difference, modern ones tend to be designed for a 20C difference. Which boiler do you have (make and exact model)?

 

[goateater]

hi
its about 8-10 years old
made by warmflow (nth Ireland) bluebird 90/120 (not a 140 sorry)
output range 26-35 kw
i also have a wood burning stove attached to the central heating system which we have on most nights from october to march

dont know what other info you want

how can they design a boiler to lose 11c or 20 c in a heating circuit, surely its the design of the central heating circuit that gives the lose of heat

 

[D_Hailsham]

bluebird 90/120 (not a 140 sorry)
output range 26-35 kw

A boiler that old will be designed for a differential of about 11C

How can they design a boiler to lose 11c or 20 c in a heating circuit? Surely it's the design of the central heating circuit that gives the loss of heat?

The output of a boiler can be calculated from the formula: kW = flow (litres/sec) x temp differential (degC) x 4.18 (Joules constant). This means that, for a given output, flow x differential is constant; the smaller the differential, the bigger the flow. Now the faster the flow, the higher will be the friction in the heat exchanger and pipes. So the heat exchanger has to be designed for the required flow rate and differential.

The output of the boiler is selected to match the heat loss from the house and the radiators are sized to give the correct heat output.

Manufacturers' specs normally quote the temperature differential or flow rate for their products.

Radiator outputs, unlike electric fires, are not constant; they depend on the flow, return and room temperatures. So you work out the heat loss of the house, select the boiler, and then size the rads to take account of the working temperatures of the boiler. Radiator specs quote the output for temperatures of 75C/65C/20C.