Direct Vent Gas Furnace: Operation and Benefits

A direct vent gas furnace, otherwise known as a direct vent heater, is the perfect residential furnace for homes, apartments, room additions, garages, and offices. This is because direct vent gas heaters do not require any outside air to function, and are the perfect size to fit into areas where space is at a premium.

These units come in 40-50 gallon sizes with an input of approximately 40,000-60,000 BTU per hour. The air is drawn in and expelled through non-metallic piping. They have energy factors as high as 0.67 which means that they are highly efficient and this counts for a huge savings on your energy bills.

How a Direct Vent Gas Furnace Works

A direct vent gas furnace has an air intake and exhaust system that is enclosed in a sealed pipe system. This system creates an air-tight combustion chamber which improves efficiency because it eliminates back-drafting.

The required air is drawn in from outside through horizontal piping in a direct wall vent and the burnt exhaust gases are expelled the same way. This negates the necessity of having to install a vertical flue through the roof. The piping system can either consist of two separate pipes, in which case two holes would have to be made in the outside wall, or it could be co-axial piping, where one pipe is inside the other, requiring only one hole to be made.

The gas flame is completely sealed inside the unit and away from contact with air in the room. All of the combustion products are vented directly to the outside of the house or room, and only clean and gentle heat is delivered into the room, in continuous circulation, for your comfort. Due to the fact that no air in the room is used for combustion it means that you can keep your doors and windows closed.


Because direct vent heaters are small, they are well-suited to smaller apartments or offices where hot water is needed but there is not much space to install another type of water heater or furnace.

There are many advantages to be had from installing a direct vent gas furnace:

  • They meet the stringent design standards of newly constructed modern homes.
  • They are safer than non-direct heaters because the unit is completely sealed and therefore no toxic gas fumes can be released back into your house.
  • A direct vent gas furnace is very efficient because it has access to air from the outside at all times, whereas a non-direct heater draws air from inside and may not have access to sufficient air which would result in a negative air pressure and inefficiency.
  • A direct vent heater is easy and inexpensive to install
  • No chimney is required
  • A direct vent gas furnace can be vented either horizontally or vertically
  • There is no electricity required so even in a power failure you will still have hot water to bathe
  • These units either meet or exceed the Energy Star standards for water heaters, which means an annual saving of between 10-14 percent on your energy bill.
  • A direct vent gas furnace provides maximum design freedom in that it can be placed anywhere within the home or the office.

Direct Vent Gas Furnace


Direct vent gas furnaces are contained in a sealed combustion box, which makes installation very easy. The best is to get a heating technician to install your direct vent gas furnace for you, as they have all the knowledge, experience and tools, but if you fancy yourself to be a handyman you could do the installation yourself.

The manufacturer generally provides a template on how to lay out the vent. An area in which there is a power outlet for the fan, which is on the inside of the heater, would be the perfect spot. Not all models have a fan, which is really only needed if the furnace is located more than four feet from the sidewall. Position the heater as per the instructions from the manufacturer. Be sure to check that there are no wires in the section of the wall to be cut or drilled into, if you are mounting the direct vent gas furnace on the wall. Follow the instructions closely as per the manufacturer.

Although you can install the actual heater, you will still need a licensed heating technician to install the ventilation and the gas line to ensure that no fumes enter the home.

Depending on which model of direct vent gas furnace you purchase, it may include a heat saving flue baffle design, factory-installed pressure and temperature relief valve, a gas control and combination thermostat, an anode rode that equalizes the aggressive water action, or a brass drain valve and aluminum vent and cap base which guard against any staining of the exterior of the building.

Many of the direct vent gas furnaces are fitted with a glass or porcelain enamel tank lining which is corrosion resistant and serves to prolong the life of the tank.

Operation and Safety

It is important that you bear certain facts in mind when operating your direct vent gas furnace to ensure that you use it safely:

  • If left standing for a period of two weeks or longer, hydrogen gas can be produced in this system. Hydrogen is extremely flammable and it is necessary that it be dissipated by opening the hot water faucet for several minutes before use in order to reduce risk of injury. Do not smoke or use an open flame near the faucet at this time.
  • If the water has been subjected to overheating, flood, fire, physical damage or the gas supply fails, switch off the manual gas shutoff valve.
  • Do not store or use flammable liquids, newspapers, rags or mops, adhesives or paint thinner near to the appliance.
  • Do not turn on the water heater if the cold water supply shut-off valve is closed.
  • Make sure that the furnace is filled with water before you switch it on.

Your direct vent gas furnace will provide you with many years of dependable use and trouble-free service if properly maintained, so it is highly recommended that you establish and follow a routine preventative maintenance program.