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Heat pumps fail homes for one reason more than any other: someone guessed instead of measured. In this episode, Amply co-founder and co-CEO Eric Fitz shares his complete heat pump sizing playbook in a talk recorded at the Building Performance Association's annual conference in Columbus.
Eric is a mechanical engineer and a self-described Manual J nerd, and he takes you through the whole chain of system design: how Manual J defines what the home needs, why duct capacity is its own separate check that can make or break a retrofit, and how Manual S picks the right equipment. Along the way he shares the quick field tricks that remove the guesswork — the ten-second flashlight test for low-E glass, the $3 tool for checking wall insulation, and why a thicker filter actually fixes high static pressure.
You'll also hear plenty of audience Q&A from the room.
Expect to Learn
- Why accurate Manual J load calculations are the foundation of successful heat pump system design.
- How infiltration, windows, insulation, and duct leakage dramatically affect heating and cooling loads.
- Methods for measuring duct capacity and identifying airflow restrictions before equipment selection.
- How to interpret heat pump performance data, including capacity, COP, latent cooling, and airflow requirements.
- The tradeoffs between oversized and undersized systems, and how proper sizing improves comfort, efficiency, and indoor air quality.
Timestamps
[00:00:00] - Episode Teaser
[00:04:06] - Heat Pump Design Fundamentals and the ACCA Design Process
[00:07:27] - Understanding Load Drivers: Temperature, Windows, and Infiltration
[00:14:02] - Window Performance, Low-E Glass, and Shading Effects
[00:20:11] - Verifying Insulation and Building Envelope Conditions
[00:26:26] - Duct Leakage, Static Pressure, and Measuring Airflow
[00:44:48] - Heat Pump Performance Data Explained
[00:52:57] - Manual S Sizing Rules and Heat Pump Selection
[01:11:07] - Balancing Comfort, Efficiency, Auxiliary Heat, and Real-World Constraints
[01:17:05] - There Is No Perfect Heat Pump: Making the Best Choice
[01:19:37] - Closing Remarks
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