Heat loss/radiator sizing.

[trialscot]

Hi,
We're renovating a 1930s end terrace and are looking at probably an oil fired central heating system.

I've done a heat loss calculation for all the rooms, how do i convert the figures for each room to give the sizes of radiators required?. I realise it isn't an exact science.

I'd like to get the pipework down while the floors are still up, just leaving the tails ready in as near as possible the right places for the rads.

 

[trialscot]

Sorry, I did a search before posting but didn't get anything useful. Have now found what i think I'm looking for -the steelrad chart.

 

[bengasman]

You don't convert figures, you compare them against the tables of the manufacturer you choose e.g found value 1111 W, you pick the one above that value.
If you have a condensing boiler, or are likely to get one in the next few years, you should add at least 10%, but more is better. Larger rads contribute to more comfort as they heat up the rooms quicker, and turn off when the required temperature is reached.

 

[Deleted member 105431]

You don't convert figures, you compare them against the tables of the manufacturer you choose e.g found value 1111 W, you pick the one above that value.
If you have a condensing boiler, or are likely to get one in the next few years, you should add at least 10%, but more is better. Larger rads contribute to more comfort as they heat up the rooms quicker, and turn off when the required temperature is reached.

I would also add larger rads enable a lower flow temp to be used and therefore with condensing boilers higher efficency.

 

[bengasman]

Don't care what everybody else says, size does matter.

 

[trialscot]

OK, so for a room with "Kilowatts Heat Loss Calculated" of 1.58kw, a rule of thumb would be a 2kw radiator and so on?.
The total kilowatts heat loss for the house is 17.47kw including DHW, so is the boiler size based on that or on the size of the radiators added together plus 3kw for DHW?.

 

[bengasman]

OK, so for a room with "Kilowatts Heat Loss Calculated" of 1.58kw, a rule of thumb would be a 2kw radiator and so on?.

That should work nicely

The total kilowatts heat loss for the house is 17.47kw including DHW, so is the boiler size based on that or on the size of the radiators added together plus 3kw for DHW?.

With modern cylinders and controls, the dhw can be left out of the equation. Heatloss calculation rounded off upwards = size of boiler, i.e. 14.47 becomes 15 kW, or the nearest upwards from there. As virtually all boilers have a fair modulation range these days, there is not technical problem with oversizing, just unnecessarily more money. If you boiler of choice would only be available in 12, or 24 kW, the 24 will be fine and cost not measurably more to run than a 15 kW model.
If there is even a vague possibility of extensions/conversions, a generous allowance would be a good idea.

 

[trialscot]

Many thanks again to all.