Modulating Furnace Automatically makes slight operating adjustments to achieve maximum efficiency Standard furnaces operate like your car in stop-and-go traffic. Fuel efficiency goes down and you're less comfortable. A modulating furnace is like highway driving, making slight operating adjustments while achieving maximum efficiency. This new condensing furnace with a modulating gas valve operates with more finesse to reduce temperature fluctuations, providing consistent indoor temperature, quiet operation, and an annual fuel utilization efficiency (AFUE) of 94%. The Classic 90 Plus High Efficiency Modulating Upflow Gas Furnace is the first to combine a modulating gas valve with a variable-speed blower. The blower has an ICM2+ (integrated control module) motor, which is more electrically efficient than that of a multi-speed blower. The furnace's gas valve operates between 40% and 100% of total capacity, in 5% increments, continuously regulating the amount of fuel burned according to the thermostat setting. The thermostat and its remote temperature sensors provide feedback for the control board, which uses "fuzzy logic" to vary valve and blower settings. Heating mode starts with the gas at 100% and the fan at 0%, the valve reducing and the blower increasing until maximum efficiency is reached. The fan then runs continuously, ramping up or down depending upon air delivery requirements. Since the fan and burner almost never run at full capacity, and energy-robbing on/off cycling is eliminated, the unit is highly fuel-efficient. Five models are available with input rates from 60,000 to 120,000 Btu/h. Additional choices include blower size, single or multi zone, remote thermostat sensors, humidifier, air filters, condensate pump, return plenum, and vent termination. 
 | Because of the modulating ability and the fact that both the air handler and valve are rarely at full capacity, the right equilibrium is found to provide the desired heat and the lowest energy consumption. This provides for the +90% efficiency. |  | Furnaces are made to last for a while, and the 5 year warranties on such units prove this. Because the blower and valve in the modulating furnace are rarely running at full capacity, lifetime is also extended. |
These systems must be installed by a professional contractor. The unit is designed only for a newly-installed, single-zone system. The furnace only runs on natural gas or propane. Not approved or recommended for use in manufactured homes.
Initial costs for modulating systems are sometimes 2 times the cost for installing the standard systems, averaging around $4000 as opposed to roughly $2500.
The savings realized by utilizing a modulating furnace, particularly in a clod climate, will be significant. A standard furnace will be notably more expensive to operate over a multiyear period, and the modulating furnace should pay itself off.
Codes require furnaces to be at least 80% efficient. At 94%, this unit is Energy Star rated.
Not Applicable
The 28" deep x 24" wide (max) x 34" high furnace can be installed in a tight space like a closet. Ducts must be sized correctly for the unit to run efficiently. A standard cooling coil can be mounted on top. Connections for gas and electric and condensate drain are accessed from either the left or the right side. The unit can only be installed by a mechanical contractor certified for this particular furnace. For a four-hour class that costs $125 to $150, the contractor gets installation/operation manuals, an analyzer tool, and certification.
There is a limited lifetime warranty on the heat exchangers and five years on all other parts, and extended service policies are available from dealers.
The modulating furnace costs $1,300 to $1,700, depending on size. A conventional furnace with 90% annual fuel utilization efficiency (AFUE) costs about $900. A complete modulating heating system, including ducts, could cost up to $4,000 installed. In comparison, a conventional system with 80%AFUE costs approximately $2,200, and a 90% AFUE system is closer to $2,900. The modulating furnace is a premium quality furnace. Although the costs almost three times as much as the least expensive furnaces, fuel savings eventually pay for the extra cost. The constant modulation allows consistency -- Rheem claims room temperatures to be within a half degree of the thermostat setting -- and quieter operation. The constant fan operation results in increased circulation and potentially improved indoor air quality. Because the home's air is constantly being mixed, temperature averaging could eliminate the need for multiple zones in some cases. Its self-diagnostics should make servicing easier. | 
