The seasonal efficiency of these units is assumed to be 90 per cent. A condensing natural gas unit heater can reduce natural gas consumption by 35 per cent compared to a natural draft unit heater.
These units cannot use a conventional chimney. The flue gases are vented outside using a special certified non-corrosive venting system since the exhaust gas temperatures are low and the combustion by-products are corrosive.
These units have a standing pilot light that is always on and use a natural draft venting system.
With a natural draft venting system, there is generally a constant flow of heated building air flowing through the venting system (chimney) and being carried outdoors, even when the unit is not firing. This energy loss is referred to as stand-by loss.
While firing, natural draft equipment will vent heated air to the outdoors to maintain a constant pressure at the burners. This air is referred to as dilution air.
The stand-by and dilution air losses could represent 10 to 25 per cent of the natural gas energy consumption for these units. It is assumed that the seasonal efficiency of these units is 60 per cent.
As of August 2008, new natural draft natural gas fired unit heaters must incorporate an electronic ignition system, which replaces the standing pilot and a vent damper, which shuts the vent system when the burner is not running and reduces stand-by loss. These regulations improve the seasonal efficiency of the unit to approximately 65 to 70 per cent.
For more information on unit heaters, contact us.