No studies were found with specific information on natural gas furnace blower usage. Therefore the approach used will be to look at the most common patterns of furnace blower usage, based on studies conducted by the U.S Department of Energy and develop the economics of High Efficiency furnaces and variable speed motor from the perspective of each of these types of usage.
Finally, some estimates of the potential overall impact based on data provided by the contractor interviews. The natural gas furnace market research identified different modes of furnace blower operation.
These are:
- Intermittent – the blower operates only when the furnace or air conditioning is operating for Heating and Cooling
- Continuous – the blower operates at low speed through the year, and at higher speeds when delivering heat or cooling.
- Seasonal Continuous – the blower operates continuously during the heating or cooling period, which is assumed to be 4 months for heating and 3 months for cooling.
- Ventilation refers to intermittent usage for circulation for part of the year. Respondents who indicated usage for ventilation indicated that the blower was used in this mode for approximately 6 months of the year.
The data for heating (burner) from Ecotope, and apply to the existing building stock. A study by the Department of Energy determined that the 2-stage furnace operates 20% of the time in high-fire mode and 80% in low-fire mode and this was used to estimate the hours for a 2-stage furnace.
The same study indicated that the blower for a single stage furnace operated about 15% longer than the burner, while 2-stage furnace runs about 7% longer, and also determined that a variable speed motor furnace equipped furnace had a stand-by consumption that was about 30 kWh / year higher than a PSC furnace as the blower motor is always energized.
The impact to the replacement customer of purchasing a natural gas furnace, including the benefit of the incentive. It also includes the cost of the increased natural gas usage required to offset the reduced heat loss from the variable speed motor furnace motor.
Comparing the monthly payment to monthly savings, the table illustrates that the package does not provide a positive cash flow if the blower is used only for heating and cooling. However increased usage provides a positive cashflow, with paybacks ranging from 3 to 6 years.
Finally, the study noted that the reduced heat loss from the variable speed motor will reduce air conditioning load during cooling operation. Using the rate for electricity from the base scenario, the annual level of savings is shown for each type of gas furnace usage.