Indoor Heating

Sizes and options ideally suited for your application

Commercial furnaces are available with heat outputs ranging from 35,000 Btu/hr to more than 400,000 Btu/hr.

Some furnaces act as part of a ducted system while others act as un-ducted space heaters.

Ducted heating systems include:

  • Gas-Fired Commercial Furnaces

  • Horizontal Gas-Fired Duct Furnaces

  • Packaged Heating and Cooling Units - the common rooftop unit

Un-ducted heaters include:

  • Floor furnace – usually used as large area heaters

  • Unit heaters – excellent for heating large open areas

Rooftop natural gas heater units and high efficiency rooftop units

Conventional gas-fired rooftop space heaters are usually mid-efficiency units with efficiency ratings in the range of 78 to 82%. They are usually purchased with air conditioning units to provide both space heating and cooling in one system. Heating capacities range from under 100,000 Btu/hr to over 500,000 Btu/hr.

A new generation of High Efficiency Gas Rooftop Units that employ modulating and condensing technology is now available.

The modulating feature can provide a small amount of heat while handling large amounts of outdoor air – a feature that will become more valuable in coming years, as the requirement for more outdoor air ventilation is expected to increase.

Condensing gas rooftop units are the most energy efficient heaters available, with seasonal efficiencies between 89% and 97%.

They include a secondary heat exchanger to extract most of the heat remaining in the combustion by-products.

Additional heat is captured from combustion exhaust gas. The exhaust gas is channeled through the secondary heat exchanger where additional heat is extracted and released into space.High efficiency systems offer significant savings to a point that it is cost effective to replace older units with new, high-efficient units.

When purchasing a rooftop unit, do not buy a unit that is significantly larger than needed, as that will reduce its efficiency. Look for systems that offer economizers, flexible flow positions and programmable controls to improve efficiency and cut costs. Also test and balance your air distribution system to gain more savings.

Unit Heaters

Typical overall efficiencies of unit heaters vary from 60% to 80% for non condensing units and as high as 93% for condensing units. Unit Heaters have relatively large heating capacities in compact casings and can project heated air in a controlled manner over a considerable distance.

They have relatively low installed cost per unit of heat output. They have intermittent fan operation that reduces electrical costs, as well as provide the advantage of redundancy in case one unit fails. Multiple unit heaters are often linked together for reliable heating in large open areas at relatively low installed costs.

Through-the-Wall Combo Heating and Cooling

These are self-contained units and come pre-wired and pre-charged providing both heating and cooling. Heat is generated by an electronic spark-ignited burner and an aluminized steel heat exchanger and is distributed through a duct system. Combustion gases are vented outside by a power vent fan, and combustion air is drawn from outside directly into the combustion chamber.

The cooling system is mounted on slide-out chasses for easy service and maintenance. The units range from 26,000 to 64,000 Btu/hr for heating and 1 to 2.5 tons of cooling for air conditioning.


A natural gas boiler is a pressure vessel designed to provide hot water or steam. It is important to specify the appropriate boiler for cost effective heating.

There are low-pressure and high-pressure boilers steam and water boilers cast-iron sectional boilers, steel boilers, copper boilers, stainless steel boilers and aluminum boilers, to name a few.

They can also be classified in terms of natural draft versus forced or induced draft boilers.

These unique and desired features should be accurately requested when specifying the boiler to match the heating needs. Therefore, it is important to specify the appropriate boiler for cost effective operation.

A properly designed and specified boiler should include full consideration of its life cycle cost, its applications and the longer term cost stability and supply reliability of the fuel it uses – such as natural gas.

High Efficiency Condensing Boilers - Condensing boilers are high efficiency boilers that capture additional energy from the combustion products by condensation of the vapour in the flue gas.

Condensation boilers will only condense if the return water temperature is below about 60º C (140º F). At part load operations, condensing boilers with lower return water temperature (say 27º C or 81º F) can have overall boiler efficiency as high as 97%.

Retrofit of condensing boilers usually requires a redesign of the radiation system to achieve the highest system efficiencies. Product data for boilers can be obtained through the manufacturers, wholesalers or dealers.

Commercial boilers are available with heat outputs ranging from 150,000 Btu/hr to more than 2,000,000 Btu/hr. When hot water is used to deliver heat, a system of insulated pipes and heating elements is used. Most boilers have a hot water supply pipe and a cold water return pipe.

Go to our Save Money & Energy section to see our Condensing Boiler incentive program.

Steam Systems

Steam systems usually have different piping arrangements and operating temperatures and pressures compared to hot water systems. Steam is the preferred method for heating a series of buildings from a centralized boiler because steam retains its heat value longer and can travel greater distances than hot water and still effectively heat a building.

Universities and hospitals are examples of settings where steam often is used. Just like hot water systems, when the heat has dissipated from the steam, the condensate is returned to the boiler for reprocessing.

As with any system, regular maintenance is required to keep a boiler system running at peak efficiency.

Radiant Panel Heating

Radiant panels can be in different formats and locations:

  • Piping embedded in ceilings

  • Hydronic wall panels

  • Hydronic floor panels

  • Embedded pipes in concrete slab

  • Suspended floor piping