Description

Improperly sized or incorrect ducting components can lead to increased air turbulence in the duct system, which increases the load on the furnace blower fan. This may lead to increased electricity use, reduction in air flow, elevated noise, frequent replacement of the filter, and increased service requirements. Poorly designed and installed ducting can also reduce the distribution of heat within the home due to excessively high or low air pressures: this can lead to poor thermal comfort for building occupants.

Challenges

EXTERNAL STATIC PRESSURE: At the pre-changeout inspection, ESP measurements should be taken and used (as a guide) to determine the appropriate retrofit furnace sizing and to identify any ductwork modifications. The ESP measurements indicate whether the ductwork is capable of moving the quantity of air that is required for the new furnace to operate within the manufacturers specifications, distributing the heat reasonably evenly without excessive noise. Significant ESP improvements can be made by adjusting the ductwork directly adjacent the retrofit furnace.

TESTING ACCESS: within the building structure, it is not possible to access the necessary ducting to take an ESP measurement. In this situation, count and measure the supply air and / or return air outlets and use a "Ductulator" (as a guide) to estimate the needed furnace sizing and ductwork modifications. Note that a combination of results is possible on both the supply side and the return side.

DEALING WITH RESULTS: Possible results of the pre-changeout ESP may result in the following:

• ESP in close /proper range
• High ESP
• Low

NOTE: When taking measurements on the return air side, the numbers will come up as negative. However, since we are only concerned with the work (CFM) the blower has to deliver, these numbers are recorded as positive.

Solutions

• Potential solutions for High ESP:
  • Drop down furnace one BTU size (suggest supplementary heat).
  • Add to the existing ductwork via a new supply/return duct.
  • Dump supply air at the furnace via a spill grill.
• Potential solutions for Low ESP:
  • After some discussion on comfort levels with the homeowner (occupant), adjust and partially close some of the return air grilles / supply air grilles in order to raise the ESP reading and then lock the grille dampers in position. Check if there are existing balancing dampers (typically near the furnace) which may be adjusted to increase static pressure. Recheck the ESP after all modifications.