For any heating system, proper sizing is critical to performance. And radiant heating panels are no different. One of the most frequently asked questions we get is how to size our SolaRay infrared heating panels correctly. When we or a dealer help someone size a system, we typically perform a heat loss calculation to help determine system sizing. There are some other tricks and guidelines however that can help you size panels for smaller projects, or ones where you might not have all the information necessary for a good heat loss calculation.
Step 1 – Measure the space
The size of the space is one piece of information you simply must have. Measure the largest rectangle you can in the room and calculate the square footage by multiplying the lengths of two adjacent sides together. For example, if your room is 12 feet wide by 15 feet long, then the room size is 12 feet x 15 feet = 180 square feet (sf).
Step 2 – Estimate the necessary wattage
Next you need to estimate the amount of heating you’ll need. This is where a heat loss calculation comes in handy. However, there are some general guidelines we use that will get you pretty close.
Supplemental System (when there are other heating systems, like a ductless or forced air doing most of the work): 2 Watts/square foot (W/sf)
Super Insulated Room (meets US EPA Energy Star standards or above): 4 W/sf
Normally Insulated Room (meets current code): 5 W/sf
Low Insulation/Drafty Room: 6 W/sf
Example – Bedroom sizing
Let’s use these steps in an example:
Our example bedroom is 12′x12′, with 8′ ceilings. It has normal insulation.
Step 1 : 12 * 12 = 144 sf
Step 2 : Normal insulation = 5 W/sf
5 W/sf * 144 sf = 720 W
Step 3 : Watt density should be 62.5 W/sf (eg a 6′ 750W panel, or a 3′ 375W panel)
Step 4 : 144/20 = 7.2
7.2 / 6 = 1.2 (round this down to 1)
7.2 / 3 = 2.4 (round this down to 2)
So, we should use either a single 6′ 750W panel, or two 3′ 375W panels for this room!
Step 3 – Determine the watt density (intensity)
Now you need to look at the mounting height (this is usually the ceiling height) of the panel to determine appropriate watt density. The higher the watt density, the more intense the maximum output of the panels.
50w/sf – eg a 120AIP4-400 is 400 watts over 8 square feet of panel – 50w/sf
This watt density is best suited for lower intensity applications, like ceilings under 8′ in height.
62.5w/sf – eg a 120AIP4-500 is 500 watts over 8 square feet of panel – 62.5w/sf
This watt density is the most versatile – readily used from 8′ ceilings up to 9’6″.
93.75w/sf – eg a 120AIP4-750 @ 750 watts over 8 square feet of panel = 93.75w/sf
This watt density is best used in places where higher intensity is desired, such as high draft areas or ceilings over 10′.
Step 4 – Figure out # of panels
We have a rule of thumb for coverage to get started here. Take the square footage of the room and divide it by 20. Divide that number by either 6, 4, 3, or 2, depending on what panel size you think will work best in the room. Round that number off and you have the number of panels you should use!
After this step, you’ll have to make a few judgement calls on the system. First, you need to make sure your wattage requirement determined in Step 2 is met by the panels you picked in Step 3 & 4 – if not, you’ll need to adjust your selection. Second, do you want more, but smaller panels, to achieve more even coverage in the space? You can use a single 6′ 750W to achieve the same heating as two 3′ 375W units. You could even use three 2′ 250W! Some people like the symmetry and distributed coverage provided by smaller units; others prefer to simply install a single larger unit – the choice is up to you.