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Heating Systems

Gas Furnaces

Furnaces burn fuel such as natural gas, liquefied petroleum gas (LPG), fuel oil, coal or wood in order to deliver hot air to the space. The most common type in Building America homes is a natural gas furnace. The majority of the gas furnaces installed in existing homes are open combustion, non-condensing fan-assist types. These furnaces have an Annual Fuel Utilization Efficiency (AFUE) between 60-80%, with a significant derating when operated at altitude. They also are normally equipped with standing pilot lights. In older homes, make-up air openings may not have been installed next to furnaces per code requirements, thus combustion make-up air is pulled from the living space. It is important to keep this in mind during an energy retrofit in order to avoid back-spill, which can be a dangerous side effect of over-tightening the space without proper combustion and make-up air openings. The Energy Savers website has extensive discussions regarding this issue. In new constructions, condensing furnaces (with AFUE above 90%) with electronic ignition-type burners are becoming common. With a separate combustion / make-up air duct that pulls directly from the outside to the appliance, a condensing furnace is categorized as a sealed combustion appliance.

Hydronic and Radiant Systems

Hydronic heating and cooling systems are not very common in Building America houses. They often require a higher skill level from the contractors and demand more maintenance by the homeowner than would be required of a gas furnace with direct expansion (DX) cooling. However, hydronic systems do not require as much head clearance as ducted systems. The piping distribution in a hydronic system is more efficient, has no air leakage concerns and is relatively quiet. Coupled with radiant cooling or heating panels, for instance, hydronic system can achieve excellent comfort levels with a more relaxed heating and/or cooling set-point. Hydronic and radiant systems are also good candidates for homes with high thermal mass. The thermal mass effect allows the system to coast through the peak demand hours with less stress on the heating or cooling systems and consequently place less demand on the utility grid. There are several active Building America team projects focused on hydronic system research, so they may become more prevalent in BA homes in the future.