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High Intensity vs Low Intensity Radiant Heat (Gas Fired)


“High intensity radiant” heat versus “low intensity radiant heat.” What’s the difference? This article outlines the characterizations of each, and what to expect when you fire ‘em up. This article covers gas-fired “low intensity radiant heaters” and “high intensity radiant heaters” (also known as spot heaters, box heaters, ceramic heaters, or luminous heaters).  Lets take a closer look..


*note – if you are looking for information on the different types of radiant heat emitted from electric radiant heaters, please visit this link from our manufacturer


Low Intensity


All radiant tube heaters are considered “low intensity.” There is a flame inside of a metal tube which takes some time to heat up and start radiating heat downward. When starting the heater cold, it takes 10-15 minutes for the heater to warm up and get to max radiant heat output. 


The idea with low intensity heat is to “bathe” an area with radiant heat, making the space consistently comfortable. High intensity radiant heaters “blast” heat to a targeted area. 


Low intensity radiant heaters are typically gas fired (natural gas or propane) and have the ability to exhaust the gasses outside. They also cover a lot of distance, with units up to 80’ in length. Substantial heat can be felt over a very large square footage area with this type of heater. They are more difficult to install since the tubes come in 10’ long sections – see the following video for more information on installing a low intensity radiant tube heater: “Are Tube Heaters Easy to Install?”


BTU outputs start at 25,000 BTUs and go up to 200,000 BTUs per unit. 


Because these units exhaust outside, people find them very safe and very effective. Most people turn to radiant tube heaters as an upgrade to traditional hot air unit heaters. Our customers find that radiant tube heaters are both more comfortable and more efficient than hot air unit heaters for most commercial/industrial applications with ceilings over 12 feet in height.


High Intensity

High intensity radiant heaters are instantly hot. The ceramic face gets visibly red hot within seconds. While these heaters can be used for whole building heating, their high intensity output makes them excellent for “spot-heating” areas from 10×10 and up to 40×40.


These units are very easy to install – simply hang the unit with chains & hook up gas/electric. 


You have a choice of 120V, 24V, or Millivolt (standing pilot) powered units. For 120V you will wire the unit directly to the power source. For 24V units a transformer is required from the power source to drop the voltage down to 24V – simple thermostat wire is wired from the transformer to the unit. For Millivolt units, no electricity is required – the unit has a standing pilot and comes with a wired thermostat. The 24V and 120V units will require the purchase of a thermostat, switch, timer, or any other control device you prefer.


The major consideration with high intensity radiant heaters is the exhaust gasses, which are unable to be vented outside. There must be enough air flow out of the building for the exhaust gasses to escape, whether it be by natural or mechanical means. “Natural means” is if the units were installed in a place with high air flow like a loading dock or a room with open louvers. “Mechanical means” can include an exhaust fan or makeup air unit that mechanically circulates the air outside. The requirement of air flow is 4CFM per 1,000 BTUs – so, a 60,000 BTU unit would require 4CFM x 6kBTU = 240 CFM. This number of 240 CFM can be used to size your mechanical ventilation equipment if needed. It is a good idea to also install a CO2 monitor, just in case the exhaust gasses are failing to flow outside.


Output options start at 30,000 BTUs and go up to 160,000 BTUs per unit. 


If you are considering this type of heater, pay close attention to the “Clearances to Combustibles” – an imaginary rectangle around the heater where you cannot have anything combustible (wood, plastic, cardboard, rubber, etc). The top clearance on these units can be high (28 inches on the smallest unit, 60 inches on the largest unit), requiring the unit to be dropped down from the hanging point using chains. The bottom clearance is the largest distance, so make sure to take measurements and make sure you can install this unit safely in your space!


*note – see this link for the clearances to combustibles numbers in inches on our DR Series (high intensity) versus this link for our HL3 Series (low intensity).




Low intensity heaters are great for covering large square footage areas, and especially preferred if you need to get the exhaust gasses outside. They provide comfort by slowly bathing an area with radiant heat while sinking that heat into the floor and room contents (tools, equipment, etc), which re-radiates back into the space.


High intensity heaters are mostly used in spot-heating applications in areas with high air flow or some natural or mechanical ventilation to make sure the exhaust gasses flow outside. These units are very easy to install and are great for spot-heating problem areas.


Give us a call, email, or fill out our Project Details form so we can start working on a radiant heat solution for your project!



Phone: (888) 501-0252