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Unit Heaters

To produce heat fan forced unit heaters burn fuel in a heat exchanger. Such devices are often used in places with many citizens, for example such areas, which have natural gas piped throughout the neighborhood.


If your space needs to be heated, the fuel, which located in your gas line, goes through a gas valve and gets into the unit heater. This fuel is ignited by the spark or pilot flame and then a flame is pushed inside a heat exchanger. When this device reaches needed level of temperature, a fan starts running and air is blown through the warm heat exchanger. The air, which goes into the heat exchanger, takes the warmth from the heat exchanger, resulting in a higher level of discharge air temperature. At the time when the fuel is burned, by-products of combustion go out from the garage heater through a vent pipe (chimney).


  • high efficiency;
  • low clearance requirements on low profile heaters;
  • most units are equipped with adjustable louvers to help in bringing hot airflow there, where you need it;
  • durability – all unit casings are resistant to corrosion and painted with a baked-on, high solid paint;
  • huge range of sizes and types to match the unit to your heating system – proper selection guarantees no worries about over or under sizing;
  • the fan can run during summer months without warmth to help circulate air;
  • devices are always ready to start their working processes – there is no need to worry about increase of your fuel supply.


  • there is a need of higher level of maintenance and service;
  • you should pay special attention to by-products of combustion – improper ventilation will result in dangerous fumes in your garage or warehouse;
  • you have to meet clearance requirements – a flame is present, so you must be ensured that combustible materials (airborne or fixed) do not get into the unit heater;
  • you should pay special attention to dirty, dusty or corrosive atmosphere;
  • dust in your garage can be kicked up by large amounts of air, moved by forced air heaters.


Air is blown horizontally into the space by unit heaters. Controllable louvers allow  vertical control of airflow. You can also find horizontal louvers that allow  side-to-side control of airflow. We can divide unit heaters  into some categories, which are based on the type of ventilation and heat exchanger design:

Types Of Ventilation:

Good Unit: Heater With Gravity Ventilation

Heater with gravity ventilation is a small device and has a low price. Due to this fact such units are a nice option for some areas. These devices have natural ventilation and do not need the assistance of fan. Heater with gravity ventilation uses the airflow in the room for the process of combustion. The warm by-products of combustion get out from the unit heater and go through a flue pipe to the outdoors. Such devices are the least expensive type of heaters; nevertheless, you have to be ensured some conditions exist, namely:

1) A negative pressure is forbidden in your space. Negative space does not allow the proper ventilation of the by-products of combustion and you will experience nuisance tripping from a safety switch that senses a blocked flue vent. Negative pressure appears when air is  exhausted from an area without any source of make-up air. Heaters with gravity ventilation can be very sensitive to changes in pressure. Sometimes start of working of bathroom exhaust fan can trip off a heater. If you have a heater with gravity ventilation that is experiencing nuisance trip outs, you may want to install an aftermarket power venter that gets installed in the flue vent pipe to help push the by-products of combustion in the right location.

2) There is a requirement of specific vent pipe routing. Heaters with gravity ventilation work on the principle that warm air goes up. The best choice is vertical venting through the roof of your room. Sidewall venting is more difficult. Venting through a roof can become more expensive since you need to completely weatherproof the hole in the roof. You have to follow the instructions of installation, given by the manufacturer.

3) During the time, when the air inside the heated room is being used for combustion, you should pay your attention to the cleanness of the atmosphere. If you are comfortable lighting a match in your warming room, then you should feel comfortable about heater working with gravity ventilation. If there are any combustible dusts (woodworking) or fumes in your room, you should select a separated combustion design (the information about this type is given below).

Heater With Gravity Ventilation – Vent Pipe Attaches To The Top
Better Variant: Garage Heater With Power Ventilation

We can compare heater with power ventilation with a unit with gravity ventilation. These devices are similar in the addition of an integral flue vent booster fan. On a call for heat, the booster fan starts working to ensure the by-products of combustion will be properly vented. Unit with power ventilation is the most common type among other heaters. The booster fan allows for greater flexibility with flue pipe routing. Horizontal venting is very simple. In a place, most venting is done through a sidewall to exclude costly roof modifications. Units with gravity venting are phased out and replaced with units with power ventilation by many major manufacturers.

Unit With Power Ventilation – Vent Pipe Attaches To Flue Vent Booster Fan
Best Choice: Heater With Separated Combustion

Today heaters with separated combustion become more and more popular. While common units with gravity and power ventilation utilize room air for the process of combustion, heaters with separated combustion are sealed from the room. Such devices consist of two flue vent pipes. First element draws in air from the outdoors and the second exhausts the by-products of the process of combustion back outside. This sealed combustion design minimizes concerns about burning the air in the room. Units with separated combustion are a can work in woodworking locations where fine dusts can ignite with an open flame. Heaters with separated combustion are usually slightly more efficient since they do not use the heated air in your room for the process of combustion.

The one and only disadvantage of heaters with separated combustion in your room is their second vent pipe. This pipe requires a one more hole in your roof or wall. Most manufacturers produce concentric vent kits that allow two vent pipes to join at a galvanized metal box on the interior of your garage. The box combines the two vent pipes on one end and diverts them into a pipe within a pipe on the discharge end. So, that, you should penetrate your roof or wall only once. This also can make your device more efficient as the warm flue exhaust warms the cold outside intake air.

Heaters With Separated Combustion – 2 Pipes Attach The Unit

Design Of Heat Exchanger:

Traditionally unit heaters are tall and narrow devices. Most manufacturers are transitioning towards the newer tubular heat exchanger design. Tubular heat exchanges are more flexible and do not break over time. This design also allows the heater to be wider and below which is useful in garages and warehouses that do not have ample overhead clearance.

Standard devices are equipped with heat exchangers, made of aluminized steel. This material is the best choice for typical warehouse and workshop installations. The average period of life of a unit heater in clean environment is about twenty+ years. If your application involves mildly corrosive atmospheres, or high humidity levels – your device will last longer if you choose a heat exchanger, made of stainless steel.

Set Of Options And Accessories:

To meet your specific requirements you should know about some options and accessories of unit heaters. Common accessories, which are used in garages, are the following:

  • high CFM blowers;
  • 2 stage units;
  • wall mounted thermostats;
  • air deflectors;
  • vent caps.

If you do know what to order, you can call us and we will give you advice  about the best option of heater to meet your needs.

Popular Questions And Useful Answers:

1) How Can I Adjust My Unit Heater?

A wall mounted 24 volt thermostat is required. When there is a need for heating, the thermostat sends a signal to the natural gas garage heater to begin working. Upgraded thermostats include a “fan” switch which allows you to use the fan with no warmth during the hot months.

2) How Much Heat Is Generated By A Gas Unit Heater?

These devices are divided by their fuel inputs. We can have a nice example – a 200,000 BTUH heater which will consume 200,000 BTU’s of fuel during one hour. The actual heating output depends on the rating of heater’s efficiency. If the heater has 70% level of efficiency, the actual warmth output will be 70,000 BTU’s during one hour. You should not choose a heater, which is based on the nominal size. Many of users think that this is the actual amount of generated warmth. In the result they will select an undersized device.

3) Where Is Better To Install A Unit Heater In My Room?

You should place it the area with lowest temperature, and it should be angled slightly so it blankets warm air across the coldest wall.

4) Where Is Better To Install A Wall Mounted Thermostat In My Room?

You should install the unit in a place, which represents a good level of average temperature in your room. If it is located in a place with low temperature, it will falsely run the unit heater more then it should. If it is installed in a place, which receives direct sunlight, it will falsely run the unit heater less then it should. The best place for your thermostat is a well insulated interior wall.

5) What Is The Right Ventilation For My Unit Heater?

You have to read carefully all the instructions of installation for your specific type of unit. Manufacturers will tell you about the common practices. Local codes may need special requirements of venting and override advices of the manufacturer. We do not recommend you to buy your vent pipe in a “kit”. There are different types of ventilation pipes, and the inexpensive kits that are designed to fit all installations are not always the best choice. A kit, which promises “flexibility”, means there are a lot of expandable parts and joints that need sealing. If you have few joints, your system will be safer. You should install your heater unit in the best possible place for comfortable heating. Also we advise you to draw a sketch of the venting required and bring it to you local supplier, specialized on plumbing or heating. Their staff will know your local codes, and they will select the parts in the longest lengths available. This saves many extra joints, which can be very dangerous, if they are sealed improperly.