Are the radiators and boiler big enough?

If you can’t get a space warm, once you know your target temperature, it’s possible to do a calculation that uses it to estimate how much heat it will take to warm the space, check the boiler puts out enough heat, and also check that the radiators and pipework deliver that heat. There are reasonable on-line calculators they might work for modern buildings, but they vary in quality and they don’t apply well to older or more ornate spaces. If in any doubt, you could get an independent heating consultant to do a survey that checks this for you and tells you what you require.

We have never seen an underpowered boiler as installers like to be very sure customers will be comfortable. Usually they are over-powered and not as efficient as they could be because of this.

The age of your system will give a hint about your radiators. If they were put in after around 1990, they’re probably generously sized already. If they are from before then, or any radiators have been removed, they may not be. Expectations about heating have risen over the years! In an old church building with the original radiators, even if they were intended to heat the air, that was probably only for a temperature of 12-14C.

More information for engineers about calculations

To check whether the size of the boiler or the radiators is a problem takes calculating the heat loss from the space, the heat output of the boiler, and the heat output of the radiators and pipework. In some “fat pipe” systems the heat output of the pipes is substantial and part of the system design.

Heat loss calculations:

• Technical method for estimating heat loss- Engineering Toolbox

• Example of a heat loss calculation tool, to help you understand the principles

Heat output of radiators and pipework:

• Estimating the output of a radiator - Engineering Toolbox

• Example data sheet for panel radiators

• Example data sheet for column radiators

• Heat loss from copper pipes - there are similar resources for other materials

• Experimental spreadsheet for calculating radiator and pipe heat output - not verified, approach with caution

• Simplified “rule of thumb” calculations for churches

Radiators are just metal and hot water at various temperature differences to the temperature of the air in the space. You don’t need data for the exact radiators you have as long as what you’ve found is similar.

The principles for electric radiators and fan convectors are the same, but you need the model number to get the heat output. The plate identifying them is often on the back against the wall where you can’t get at it but sometimes you can find specific enough user manuals on-site to identify them.

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