Steve Hanson, an HVAC instructor at Coconino Community College, said system sizing should be based on the building's envelope rather than solely on individual rooms or equipment labels. "So system sizing is based on the envelope," Hanson said, describing factors technicians consider when determining heating and cooling loads.
Hanson said technicians assess window construction (single-, double- or triple-pane and whether panes are argon-filled), the quality of insulation, and whether a structure was built to older or newer, higher-efficiency codes. "We need to understand all of that because it's the amount of BTUs the structure loses in the heating cycle or gains in the cooling cycle that we need to understand to make sure that the equipment replaces that loss so that it heats or cools and keeps the occupants comfortable," he said.
The instructor noted that older buildings can present different challenges than modern construction. He gave the example of a building from the 1950s that still uses tar paper for insulation, contrasting that with recent construction that typically meets higher efficiency standards. Hanson said those differences change the calculation of how much heating or cooling capacity — measured in BTUs — a system must provide.
Hanson, who said he spent about 26 years in the HVAC industry before retiring and now teaches HVAC, electrical and plumbing at Coconino Community College, framed sizing as an evidence-based process: evaluate the envelope, quantify heat loss or gain, and select equipment sized to replace those losses. He added that while a single room within a building can be sized separately, the standard approach is to treat the structure as an envelope for load calculations.
No formal actions or votes were taken on this topic during the meeting.