Furnace energy usage and filter pressure drop was measured for forced-air heating/cooling systems in ten California homes. Each home was monitored for at least one year. Measurements were made of the blower energy, filter pressure drop, supply and return plenum pressures and temperatures as well as indoor temperature. At least two filter types were installed, including a MERV 16 filter, in most houses. As the filter became dirty, in some homes the blower energy usage increased and in others the blower energy usage decreased. Increasing blower energy usage was associated with BPM blower motors and decreasing blower energy was associated with PSC blower motors. There was a large pressure drop across the MERV 16 filter as compared to the lower MERV filters. Many homeowners complained of noise because of the large pressure drop and air bypassing the filter.

In addition to field measurements, simulations were made for a typical new home in six California climate zones, with combinations of PSC and BPM blowers, and low and high duct leakage. The results indicate that for MERV 10-13 filters, as compared to a baseline of MERV 5, the effects on blower energy use are moderate (less than 5%) over a wide range of performance conditions and climates. Using MERV 16 filters leads to problems in terms of noise, usability and potential for significantly increased blower energy use (about 20%). In systems that are already close to blower performance limits with low MERV filters, the addition of a MERV 16 filter pushed the blowers to their performance limits. The effect of filter loading on total HVAC system energy performance was small (less than 1%) for most homes. However, with high filter loading rates for MERV 16 filters the performance deteriorated significantly (up to 20% increases in energy use for a system with leaky duct and a BPM blower) indicating that a filter loading indicator should be required for MERV 16 filters.