One for the plumbers / Heating engineers
Discussion
Need to know what output in BTU's for a radiator for the following;
New single storey extension onto existing kitchen diner
Internal dims 5.70m long, 2.50m wide, 2.30m high
Flat insulated roof
Double glazed roof lantern 3.0m x 1.5m
Double glazed Bi Folds 3.5m x 2.1m
2 outside walls with cavity insulation
Concrete insulated floor
Have tried using 5 online calculaters and got 5 different results ranging from 2500 to 9800 BTU's
New single storey extension onto existing kitchen diner
Internal dims 5.70m long, 2.50m wide, 2.30m high
Flat insulated roof
Double glazed roof lantern 3.0m x 1.5m
Double glazed Bi Folds 3.5m x 2.1m
2 outside walls with cavity insulation
Concrete insulated floor
Have tried using 5 online calculaters and got 5 different results ranging from 2500 to 9800 BTU's
The calculators seem bonkers - when the whole system was replaced in my daughter's house the rad sizes produced seemed ridiculously small. They assume flow temps that you wouldn't want with kids around and anyway modern condensing boilers are supposed to have low flow temps. If you drop the flow temp the rad needs to be up-sized dramatically.
We got the fitters to use rads that fitted well in the space available. Apart from anything else, the rated ones would have been so small as to look silly in the space vacated by the original rads.
We got the fitters to use rads that fitted well in the space available. Apart from anything else, the rated ones would have been so small as to look silly in the space vacated by the original rads.
When sizing a radiator all you need are the heat requirements for the room.Once calculated select the radiator with the correct output that suits the space available,there will be several different sizes and profiles of the same output available.Be aware of heat distribution,large rooms may need more than one radiator to give a balance of heat and no cold spots.
bazjude2998 said:
...select the radiator with the correct output....
OK - but my point is that it will only be the correct output if the system matches the parameters that were used to determine the radiators output - the Delta T figure. If the flow temp is lower than used to rate the radiator then its output will be lower.I don't know - maybe it's nonsense? The older guys who installed the system in my daughters house did a great job at the actual plumbing bit. But they seemed to have no idea about condensing boilers and couldn't explain why the Worcester Bosch instructions said to run the boiler 'stat at 1.5 (out of 6). Using the rad sizings the guys suggested would have needed the boiler to be on max.
Sheepshanks said:
couldn't explain why the Worcester Bosch instructions said to run the boiler 'stat at 1.5 (out of 6). Using the rad sizings the guys suggested would have needed the boiler to be on max.
What boiler is it? Mine is a WB and has flow temp display. 1.5 out of 6 sounds woefully low but mine has no such markings...As for the rad, as above you can always turn an oversized one down, you can't turn an undersized one up.
Dave_ST220 said:
What boiler is it? Mine is a WB and has flow temp display. 1.5 out of 6 sounds woefully low but mine has no such markings...
It's a Junior Combi.This is from the user instructions:
"CENTRAL HEATING SYSTEMS WITH ROOM THERMOSTAT/THERMOSTATIC RADIATOR VALVES
With modern heating systems set around a 20 °C heat loss, the optimum setting for a condensing boiler will be approximately between one and two on the central heating temperature control. The system must be balanced correctly and the radiators may need upgrading. This allows the boiler to condense as much as possible for the central heating system.
The temperature of each room can be set individually (except primary room with the room thermostat) using the thermostatic radiator valves."
I think this is a bit extreme, and I'm aware that some CH fitters think condensing in nonsense.
However my original point to the OP is that to get rad sizing right you need to know the system's usual flow temp as the calculators assume a flow temp that is probably higher than most people use.
Dave_ST220 said:
For the boiler to condense the return flow temp can't be too high IIRC??
Yes - below 57C I think.So the flow temp can't be too high as the system can't lose all that much heat - especially if the rads are small. And with lower temps the small rads are likely to be inadequate, so it's a double whammy.
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