QUESTION: I should replace my old gas furnace. Does a new super-efficient model make sense in a mild climate? Which ones provide the best comfort, and will variable-speed, variable-output models save more?
ANSWER: If you are concerned about comfort and indoor air quality, a super-efficient variable-speed, two-stage heat output gas furnace is best. A savings of 40% to 50% of your heating costs (gas and electricity) is typical.
In a mild climate, it will take many years for the savings to pay back the cost of a super-furnace. If you plan to install a super-efficient central air conditioner now or in the future, the electronic controls and air handler in the super variable-speed furnace are often required anyway.
Other than in the coldest weather, only 10% of the time, a two-stage furnace operates in the extra quiet, low-heat output and slow blower speed mode.
This reduces indoor temperature swings and that initial gust of cold air followed by a blast of hot air each cycle. This is because the furnace runs longer each cycle in the low-heat stage. These furnaces are extremely quiet.
Variable-speed blowers use either electrically commutated or integral controlled motors. On continuous air circulation so the air cleaner works continuously (for allergy sufferers), the savings in electricity for the blower is $300 per year.
Do not compare just the annual flue utilization efficiency ratings to determine the most efficient models because testing regulations have not kept up with the newest technologies.
Gas furnaces are tested only in the highest output mode. The electricity savings from the motors are not taken into account.
Single-stage, single-speed gas furnaces typically cost several hundred dollars less than two-stage models. They too use stainless steel condensing heat exchangers. These capture nearly all the heat from the gas for your house.
Condensing furnaces are simple to install because a chimney is not needed. The exhaust gases, only 140 degrees, are vented outdoors through a two-inch plastic pipe. Switching from expensive electric to gas heat is simple.
Sealed combustion designs reduce drafts and minimize hazards of carbon monoxide poisoning. The combustion process is sealed from indoor air.
A small plastic pipe carries outdoor combustion air into the side of the furnace. The burners are sealed. An induced draft fan sucks the air through the burners and forces the exhaust gases outdoors again.
Write for Update Bulletin No. 610 showing a buyer’s guide of 21 super-efficient single- and two-stage furnaces listing heat outputs, efficiencies, blower speeds, dimensions, sealed combustion and a savings payback chart. Please include $2 and a business-size self-addressed, stamped envelope and mail to James Dulley, Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, OH 45244.
Letters and questions to Dulley, a Cincinnati-based engineering consultant, may be sent to James Dulley, Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, OH 45244.