Oversized Furnace Analysis for Heat Pump Installation

This was inspired by Technology Connections’ recent video on how most of the US has vastly oversized furnaces, which is holding back heat pump installation. BeeStat has a ton of information on furnace run time. What I would love is for it to be able to spit out a “recommended heating capacity” metric (and cooling for that matter). At a basic level:

  • The user would input the tonnage of their current AC as well as the furnace BTUs and AFUE
  • BeeStat iterates over the data it has available to it. On the coldest and warmest days of the year, it analyzes the data hour by hour. If it’s -5 degrees outside and the furnace is running only 20 minutes per hour, the furnace is oversized by 3x.
  • The AFUE of the furnace would need to be taken into account, plus a margin of error. Additionally, night vs day should be taken into account. Furnaces have to work harder at night due to the lack of natural heating, while air conditioners have to work harder during the day due to natural heating via the sun.

Eventually the feature could get fancy with things like a tolerance limit for when secondary heat sources such as heat strips would need to kick in.

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Interesting idea, but how would you determine the initial need? It’s done now by area, location, heat loss through windows, insulation, and more factors. The HVAC installed in my home doesn’t look over-size. Beestat says that it can keep up from -17 to 105. Where I live, it can get to -20 and 101, so based on the initial computations, I’m sized right.

It’d need too much information to be accurate for sizing as you’d have to provide numbers that may also be best-case manufacturer provided numbers.

You can already see the information about balance and system performance in the analyze tab to tell you at what outdoor temp your system cannot keep up. This is a safer metric as it measures actual performance and not theoretical. An HVAC professional would then need to verify system operation (refrigerant temps, restriction, airflow) to determine if the system was operating at its peak performance to then adjust system ratings to actual output/needs.