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is this boiler too small?
- Thread starter matz
- Start date
Why not - on paper my house only needs 11kW.
The Whole House Calculator is shyte, but if anything it over eggs the pudding.
The calculation method you used is reasonably accurate, provided you use the same type of rad, i.e. single or double panel.
However you need to use the 50C value to get the correct output. This because the temperature quoted is the difference between the room temperature and the mean radiator temperature. If you use the 60C value, you are assuming that the average rad temperature is 80C, which would mean a flow temp of 85C and return of 75C. This is the historic method I referred to earlier.
Radiator outputs are now quoted for a flow of 75C, return 65C and room temp of 20C. This gives a mean difference of 50C, which is the value you should use.
Your 19kW of rads is really only 14.8kW, using plumbworld's btu figures. which is about the same as the boiler output. However, there's a catch.
You boiler is designed to work with a 20C difference between flow and return. If you run the radiators with the same difference their output reduces by about 17%, so the 14.8kW becomes 12.3kW. This could account for you feeling colder than you are used to.
You really need to use the calculator I posted the link to, so you know what size boiler you really need. When you have done that, post the results.
Only just seen this; 8.5kW could be correct. If you post the data you input I will check it.
It's quite common for people to have more heating available than they usually need. A modern boiler will modulate its output down (reduce the flame size) to try to match the demand. This helps it run more quietly, and is more efficient than on/off cycling. Big radiators can be run at a cooler temp that little ones, which I think makes the room more comfortable.
Extra capacity can be useful:
- in abnormally cold weather, when it can cope with extra demand
- to warm the house up more quickly, for example if you are often away on business in winter (I found this, in the days before programmable room stats, which are fantastic).
- if you are having several hot baths in quick succession, in cold weather, when the cylinder will be drawing heat and reducing that available for the radiators.
Good controls, especially TRVs and zoning, means that you will not often have to heat every rad in the house to the max at the same time.
Extra capacity can be useful:
- in abnormally cold weather, when it can cope with extra demand
- to warm the house up more quickly, for example if you are often away on business in winter (I found this, in the days before programmable room stats, which are fantastic).
- if you are having several hot baths in quick succession, in cold weather, when the cylinder will be drawing heat and reducing that available for the radiators.
Good controls, especially TRVs and zoning, means that you will not often have to heat every rad in the house to the max at the same time.
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Unless pump and pipework is capable then an oversized boiler will mean Jack ****e regards faster heat up times.
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