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W. Tombling Ltd.
Wembley House
Dozens Bank
West Pinchbeck
Spalding
Lincolnshire
PE11 3ND
U.K.
You are here:- home > heater index > radiant heating index > wall mounted radiant heaters > Calculating radiant heater sizes
Radiant heat load
The radiant heat load is the amount of infrared energy needed to heat a given area; it is expressed in kW per square meter (kW/m2).Calculating the radiant heat load
Our on-line radiant heating calculator will estimate the required
radiant heat load for an area given its dimensions and construction.To manually calculate the radiant heat load for a building, determine its area (in square meters) and multiply by the factors given in the table below:
| Building type | Multiplying factor |
| Small building with good insulation or suspended ceiling | 0.08 |
| Large room or area with good insulation, upto 3 meter ceiling height | 0.1 |
| Poorly insulated area with high ceiling and concrete floor | 0.15 |
| Uninsulated building where reasonable levels of comfort are required | 0.2 |
| General heating in a large building or workshop | 0.25 |
| Zone heating for an area with little or no heating | 0.45 |
Step One
Calculate the area to be heated in square meters.
Area (m2) = Length (m) x Width (m)
Step Two
From the table above, select the factor that most closely matches the building type.
Heat load (kW) = Area (m2) x factor
Step Three
Select Activair infrared radiant heaters that match or slightly exceed the required heat load.
Practical considerations
For uniform heat distribution it is better to use several smaller radiant heaters mounted on opposing walls than one large one. See installing ceramic infrared heaters for further details.Example
A small industrial unit is to be heated using Activair infrared heaters. The unit is made up of two areas. A workshop, which has a large roller shutter door that is often left open, and a smaller office area (C).
For the purpose of calculating the radiant heat load the workshop has been split in two, marked (A) and (B) on the drawing. This is to allow for extra heating in the loading bay to counteract cold drafts.
The customer wants to know the running cost of the radiant heaters. From his electricity bill the cost of one unit of electricity is £0.20
Radiant heat load for Area A
Area (A) = 5m x 5m = 25m2
Zone heating is chosen from table (A) allowing for extra heat to compensate for the doorway.
Heat load for Area (A) = 25 x 0.45 = 11.25kW
Two HS6000 6kW wall mounted radiant heaters are selected.
Radiant heat load for Area (B)
Area (B) = 10m x 5m = 50m2
Area (B) is poorly insulated with a concrete floor, so from table (A) a factor of 0.15 is selected.
Heat load for Area (B) = 50 x 0.15 = 7.5kW
In order to provide uniform heat distribution four HS2000 wall mounted radiant heaters are selected.
Radiant heat load for Area (C)
Area (C) = 5m x 5m = 25m2
Area (C) is well insulated with a 2.5m ceiling, so a factor of 0.1 is selected.
Heat load for Area (C) = 25 x 0.1 = 2,5kW
Because radiant heaters work best when they are positioned on opposing walls two HS1500 wall mounted radiant heaters are selected.
The industrial unit has a total radiant heat load of 21.25kW and can be heated using 8 wall mounted radiant heaters.
Hourly running cost
To calculate the running cost per hour, add together the radiant heater sizes and multiply by the cost of one unit of electricity.
Total radiant heater capacity = (2 x 6) + (4 x 2) + (2 x 1.5) = 23kW
Running cost per hour = 23 x 0.2 = £4.60
The actual running cost is likely to be less. By selecting energy saving controls, the wall mounted radiant heaters will only be turned on when needed.
Radiant heating is very economical
Radiant heating is inexpensive to install and run. It is ideal for industrial buildings, with high ceilings, open doors, large heat losses etc. Because its output can be directed exactly where it is needed, energy is not wasted heating unused areas. By using energy efficient controls that turn the radiant heaters on only when they are needed running costs are kept to a minimum. For further information see the radiant heating homepage.You are here:- home > heater index > radiant heating index > wall mounted radiant heaters > Calculating radiant heater sizes
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