ACHR News recently ran an interview piece, Electrification Changes Heat Pump Design and Specification for MEP Engineers, built around IES Vice President Matthew Duffy. Per the outlet's summary, "heat pump specification is becoming more complex," and the challenges it names are sizing, electrical capacity, and commissioning. The story is aimed at MEP engineers, the people who design mechanical, electrical, and plumbing systems for larger buildings. I am not going to claim what Duffy said beyond that summary. But those three words make a useful frame for a homeowner holding a heat pump quote, because every one of them can go wrong in a house, too.
What follows is my own translation to the residential side, not a description of the article's contents.
Sizing: ask to see the math
A quote that says "3 ton" or "4 ton" with no supporting numbers is a guess wearing a model number. The industry-standard way to size equipment for a house is a room-by-room load calculation, commonly called Manual J. The equipment selection step that follows is called Manual S, and the duct design step is Manual D. You do not need to run these yourself. You need to ask whether one was done for your house, and ask for a copy.
Then check the inputs against reality. Does the report list the right square footage, the right number of windows, the right insulation levels? If your attic was reinsulated or your windows were replaced, did the calculation know? A load calculation built on a stale assumption produces a confident wrong answer. Also ask what the contractor sized to: heating load, cooling load, or whichever was bigger. A heat pump has to do both jobs, and in a cold-winter climate the two numbers can be far apart.
Existing ductwork is part of sizing, too. If the old system had marginal airflow, a new outdoor unit will inherit that problem. Ask whether the duct system was evaluated or simply assumed adequate.
Electrical capacity: read the nameplate, then look at the panel
This is where a multimeter earns its keep, within limits. Start with paperwork rather than live work. Every outdoor unit carries a nameplate listing minimum circuit ampacity and maximum overcurrent protection. Ask the contractor for those figures from the model they are quoting, then compare them to what your home has.
Look at the main breaker rating on your panel label and at the breakers already installed. Note whether there is open space for a new double-pole breaker. Count the big loads you already own: electric range, dryer, water heater, EV charger, well pump. Ask the contractor whether a load calculation was done for the service, or whether they simply looked for a free slot. A free slot in the panel is not the same thing as spare capacity in the service.
Do not open the panel cover unless you know how and are comfortable with it. The meter is better used for things like confirming that the disconnect near the outdoor unit is live or dead when it should be, and for checking supply voltage at an outlet to get a sense of how your service behaves under load. If the quote involves a panel upgrade or service change, that is real money and often a permit and utility coordination matter. Ask for it as its own line item so it is not buried.
Commissioning: the step that never shows up on the box
Commissioning means proving the installed system actually performs as designed. A unit can be physically bolted down, wired, and running, and still be set up poorly. Ask the contractor what they measure at startup and whether they will leave you the numbers. Reasonable items to request:
- Refrigerant charge verification method, and the readings recorded.
- Measured airflow or static pressure across the indoor unit, not just "the fan runs."
- Temperature split between supply and return air once the system settles.
- Confirmation of condensate drain operation and a float switch where one is called for.
- Thermostat and controls setup, including any settings the installer changed from defaults.
Then do your own pass. Put a simple probe thermometer at a supply register and the return grille, note the readings in your own log, and repeat on a different day. You are not replacing the contractor's instruments. You are building a baseline so that next winter, if comfort drifts, you have something to compare against.
How to use this before signing
Put the three topics in an email to every bidder: please send the load calculation, the nameplate electrical data for the quoted model along with your assessment of my panel, and a description of your startup and commissioning checklist. The answers sort bidders quickly. A contractor who responds with documents is telling you how the job will go. One who responds with "we always put in a 4 ton" is telling you something as well.
None of this makes a heat pump a bad purchase. It makes the purchase a specified system rather than a swapped box. If the trade press is right that specification is getting harder, then homeowners are the last people who should treat the quote as simple.