Radiator sizing calculators

[astee]

Hi all,

I've been reading through some previous posts, but still not too confident that I've got the answer to my specific need.

I'm looking to install radiators into 2 rooms which do not currently have any installed.

The house is a Victoria midterrace, solid wall (~220mm), ~100cm insulation pitched roof. Both rooms have heated rooms below (suspended ground floor). With a 3 year old condensing boiler that I would like to run as close to optimal (50c?).
Would oversizing the rads help achive this and are there any downfalls to consider if doing so (higher bills)?

The results from calculators are wildly different, some having almost 1000BTU/300W differences with the same spec, so unsure what I should be looking for.

Office size:
H: 2.83m
W: 2.82m Single external wall
L: 3.4m
Double glazed window:
H: 94cm
L: 161cm
(1.52m²)
SW facing

Bedroom size:
H: 2.83m
W: 4.6m Single external wall
L: 3.5m
2 double glazed windows:
H: 92cm
L: 163cm
(3m²)
NW facing

Cheers

 

[Dereekoo]

Just do the calcs and pick the highest, it will be better than not doing any calcs

 

[astee]

Did just that in the end.

Do you have any opinion on...?

"With a 3 year old condensing boiler that I would like to run as close to optimal (50c?).
Would oversizing the rads help achive this and are there any downfalls to consider if doing so (higher bills)?"

 

[Dereekoo]

My opinion on trying to control return temp to boiler is "pie in the sky" prospect. How much heater a radiator gives out so the temp reduces from 70 (say) to 50 from inlet to outlet depends on what the temperature of the room is at any one time, what restriction the lockshield valve is set at and what number the thermostatic valves are set at, it would be bad enough with one radiator but with several working in conjunction with each other BUT if you assume a certain temperature in all the rooms and everything is set up to send the required flow to each radiator then you can in theory size each radiator correctly for each room for this once in a lifetime event, throwing in another parameter of over sized radiators obviously messes up any calcs you have made. Personally I think as long as you have thermostatic valves on a radiator is doesn't matter what the size is as the flow to it will be restricted as and when required and the gas consumption and hence bills will stay the same more or less but as stated earlier any logical heat loss calcs to attain the 50c goes out the window.

 

[vulcancontinental]

how does 1.1kW and 1.6kW respectively match your results?

 

[flameport]

With a 3 year old condensing boiler that I would like to run as close to optimal (50c?).
Would oversizing the rads help achive this and are there any downfalls to consider if doing so (higher bills)?

Oversized radiators is the only way to achieve that if you want the building to be heated adequately.
That's oversized compared to having a flow temperature of 70C - adjustments can be made for radiators to determine their heat output when used at lower flow temperatures such as 50C. It's not just a case of bunging in a massive radiator.

The advantage is lower fuel bills for the life of the heating system.
The disadvantage is larger radiators that cost more to buy, but that is a one time cost and insignificant compared to the savings in gas over many years.

 

[ericmark]

Never quite worked it out, it is clearly down to time, if a 1 kW heater can get a room up to temp in 1 hour, likely a 2 kW heater will do it in ½ hour, not quite that simple, but using geofencing speed is important, but so is timing.

If the boiler is 20 kW and your due home at 6 pm, then you will not use all the rooms at 6 pm, so likely will use say dinning room, living room and kitchen, so the combined radiators for the three rooms need to transmit 20 kW into the rooms. If the boiler can modulate to 6 kW then there could be a case to just sink 6 kW.

Distance at which the geofencing switches on is also a consideration, if it take you an hour to drive home then the radiators can be ½ the size to if it takes you 20 minutes to drive home.

If the boiler is small, then you can stagger the heating of each room, a 10 minute delay kitchen to dining room to living room, can give the kitchen a really good boost, but often this needs simple time rather than geofencing as often you can't set distance.

In the old days of heating the home 24/7 you were only interested in loses, but today we are looking at speed. The radiators in my house are clearly too small, the heating is switched off over night, and in the morning I reheat the rooms, but the boiler cycles off/on so clearly not putting the full 20 kW into the rooms, there are 14 heated areas, in the main 4 are not used in Winter, so 10 in real terms, the shower room and bathroom both heated 24/7, one room has two radiators, but TRV's are not linked, they just have the same schedule. My boiler does not modulate.

I work less than 5 minutes from home, so geofencing does not work, all set by time, but my radiators are really under sized, which means CH needs to go on at least an hour before due home.

Last house living room had a 4 kW standard radiator, plus a 3.5 kW fan assisted radiator, and a 4.5 kW gas fire, no need for geofencing room took 10 to 15 minutes to warm up.