Condensing Rooftop Units

A relatively new technology in British Columbia, condensing rooftop units are the most energy efficient gas-fired heating and ventilation system currently available on the market.

These units provide a higher combustion efficiency because they contain a secondary heat exchanger. The exhaust gases pass through this additional heat exchanger, lowering the exhaust temperature to the point where the water vapours in the exhaust condense. This enables the unit to recover latent heat that would otherwise be lost to the exhaust air, improving the unit’s efficiency.

In 2011, Prism conducted a pre-feasibility study for Fortis BC to evaluate the natural gas savings potential of condensing rooftop units for Multi-Unit Residential Buildings (MURBs) and commercial buildings. The study estimated that if condensing rooftop units were implemented in the MURB market province-wide, the resulting decrease in natural gas consumption would range from 200,000 – 550,000 GJ per year.

Condensing rooftop units require a condensate drain line to be installed through the roof to transfer condensate into a neutralization tank, which then empties into a normal drain. Manufacturers usually provide an enclosure to protect the unit, particularly if it will be exposed to freezing temperatures.

The initial cost of these units is higher than conventional systems because they contain a secondary heat exchanger and require condensate drainage and freeze protection.

Condensing Rooftop Units Highlights

  • Between 89% and 97% efficiency; the most efficient gas-fired heating and ventilation system available
  • Potential annual heating energy savings for BC MURBs is estimated at 0.0157 GJ / CFM for makeup air units
  • Potential annual natural gas reduction for BC MURBs is estimated at 200,000 - 550,000 GJ/yr.
  • 18-20 year expected equipment life-span