Infrared Tube Heater Sizing

Infrared Tube Heater Sizing

How to Size Infrared Tube Heaters

You decided to install radiant heat in your building. Fantastic! What’s next? How many heaters do I need? What size tube heater is ideal?

These are important questions. If you oversize your heaters, you will waste money on equipment and your heaters will cycle more often, increasing maintenance costs and reducing efficiency. If you undersize your radiant heaters, building personnel will be cold and you will be left needing to spend money on additional heat in the future. In this article we will quickly discuss what goes into choosing correct heaters for your building. Let’s jump in!

There are several factors to consider when selecting the size and quantity of heaters for a building. In theory, heating a space is simple math problem based on the outside temperature and the size of the building. In actuality, many factors need to be accounted for to ensure the comfort of a space and install the most efficient infrared heating layout.

Say a large building requires 1 million (1.0 MM) btu/hr to keep the space temperature 70°F. If a single heat source was placed in the middle of the space to produce 1.0 MM btu/hr, the space would be kept at that constant temperature it if had uniform heat and air distribution. Why not just use one large heater for an entire space then? The reason is that no space has perfect air distribution. Overhead doors, man doors, intake/exhaust locations, building shape and roof shape all play a role in how the air flows through a space.


The major advantage of radiant heat is that it reduces the concern of convection. Gas fired radiant tube heaters heat the floors of a building with their infrared rays. When a person is standing underneath a radiant heater, it feels warmer than the equivalent sized forced air heater. This is because they are feeling the radiant warmth from above and from the heated floor below them. Compared to forced air heat, radiant heat can be kept 5°F cooler with the same comfort level! This is important to understand - it means that floor coverage of the tube heaters is just as important as correct sizing.

Cold Areas

Considerations for the convective heat flow cannot be ruled out entirely. Overhead doors are a large source of cold air infiltration into a building - even when they are closed because they provide less insulation than a wall. Oftentimes, a heater is placed closer to an overhead door or a larger BTU U-tube configuration heater is installed. This provides additional heating capacity to maintain comfort near the door and quickly reestablish the desired space temperature after a door is closed again. Centering heaters in a building can work well for small shops, but for larger spaces it is important to have coverage near the outside walls. Cold walls act as a heat sink and experience reveals that if the outer area of a room is warm, the center of a room will remain warm as well.

All buildings have code ventilation requirements that differ depending on their use and service. Exhaust fans and intake louvers determine the amount of additional cold air entering the building. This additional air must be heated to maintain space temperature.


Building insulation is always taken into account when we perform our heat load calculations. Most contractors and owners are aware of the importance of insulation – and they are correct! Radiant Energy Systems makes sure that the heating capacity matches the true requirements of the building. The beautiful thing is insulation can always be improved after heat is installed. The heaters will simply run less often and money will be saved due to reduced gas demand.


The team at Radiant Energy Systems has 100 plus years of combined heating design experience. We are here to help contractors and owners with new system designs. There is always more than one way to design a heater layout, and we can explain the costs and benefits of multiple solutions so that you can make an informed decision.

Call our experts now to discuss the best heating layout for your building!