Here's the short version before I get into the scar tissue: Heat pump water heaters beat tankless units for most small commercial buildings. A portable Midea dehumidifier is a temporary fix for a real HVAC problem. And if you're ordering a McQuay fan coil unit or McQuay thermostat without verifying the exact control protocol, you're about to waste money. My own mistakes in these categories cost roughly $38,000 over a decade. Keep reading to avoid the same autopsy.
I'm a facilities manager for a 40,000-square-foot mixed-use building on the East Coast. I've been ordering HVAC service and replacements for about 14 years — 13 if I don't count the year I just followed my boss's guesses. I've personally made and documented 23 significant mistakes. One of them earned a permanent spot in our annual training deck. Now I maintain a checklist that starts with 'call the person who actually knows.' This article is basically that checklist, minus the embarrassing photos.
The McQuay Fan Coil Unit Trap
In 2021, I ordered 14 replacement thermostats for McQuay fan coil units. I had the McQuay model numbers. I had the old thermostat part numbers. And I still got it wrong. The units were using a 0-10V proportional signal from the thermostat; I ordered 24V floating control models. They arrived, snapped into the same backplate, and did absolutely nothing except blink. That cost $1,600 in parts, one week of wall repair, and a very red face in the morning staff meeting.
Here's something vendors won't tell you: 'McQuay thermostat' isn't one fixed product. McQuay, now part of Daikin Applied, has manufactured fan coil units with multiple control schemes over the years. Some use simple line-voltage thermostats. Others use a factory controller and a remote sensor panel. A universal thermostat marketed as compatible with McQuay may work with one generation and not the next.
Before you buy anything, collect four things: the exact fan coil unit model number, the controller generation (for example, MicroTech or the older analog controls), the control signal type, and the piping configuration (2-pipe or 4-pipe). Snap a photo of the nameplate. Don't trust the building drawings; in this industry, drawings are fiction half the time. (I really should have learned that by 2021.)
The same rule applies to valves and actuators. A McQuay fan coil unit from 2008 can use a different valve linkage than a 2015 unit. I found out on a $3,200 order of zone valves. That one also ended with 'my fault' on a work order.
One more historical note: the idea that all McQuay thermostat parts are interchangeable goes back to a simpler era with fewer factory options. That era is gone.
Mr. Heater and Midea Dehumidifier Are Band-Aids, Not Solutions
After the thermostat disaster, I became more careful. But not careful enough to stop buying band-aids. Our loading dock corridor gets clammy every summer, and the nearby FCU condensate line had a persistent blockage that we kept 'watching.' I bought a Midea dehumidifier rated for 1,500 square feet and pointed it at the hallway. It pulled water. It also filled up every four hours, and the room still stayed humid enough that the floor tile adhesive puckered.
The dehumidifier wasn't the answer; it was a clue. When we finally cleared the condensate line and re-leveled the FCU, the hallway dried out without the Midea unit running past the first week.
Same story with cold drafts in the entry vestibule. I grabbed a Mr. Heater propane radiant heater as a stopgap. It did exactly what a propane heater should do: warm, loud, and perfect for a garage. In a commercial building, the portable option brings ventilation concerns, fuel storage, and eventually a $450 compliance citation I still think about at night. The real fix was a small electric unit heater, mounted properly with a thermostat. The Mr. Heater went home with a coworker.
Here's what I'd say if you're feeling the same impulse: use these products for what they are — temporary tools. Midea makes reasonable consumer dehumidifiers. Mr. Heater makes capable portable heaters. But neither belongs in a commercial 'set it and forget it' system. When a portable appliance seems like the solution to a building problem, treat it as a diagnostic signal.
Heat Pump Water Heater vs Tankless: What I'd Pick Now
Now the decision you probably searched for: heat pump water heater vs tankless. I went back and forth for two weeks. Heat pump water heater had lower annual operating cost. Tankless had unlimited hot water and took less floor space. Our building has a small office bathroom and a break room, so peak hot water demand is modest. I chose a heat pump water heater, and I'd make the same choice today for this building. For most small commercial buildings, heat pump beats tankless when you can spare the floor space.
Tankless wasn't a bad product; it was the wrong fit. The tankless gas model we considered had a high firing rate, which meant a bigger gas line from the main supply. That change plus the venting retrofit added $1,200 to the job. The heat pump model fit in the existing mechanical closet, had access to enough air volume, had a condensate drain nearby, and we found a $600 utility rebate as of December 2024. The projected payback came in around 2.3 years.
According to ENERGY STAR's product comparison (accessed January 2025), heat pump water heaters are about three times as efficient as standard electric resistance models. For a low-draw commercial space, that efficiency outweighs the tankless benefit of endless hot water. But that's not a universal answer. If you're designing for a 200-seat restaurant, tankless or a commercial condensing water heater will probably serve you better. If you don't have 700 cubic feet of air space or a floor drain, a heat pump model may not work even if the math looks good. Local codes and venting requirements will have the final word.
What I Won't Touch (and You Sometimes Shouldn't Either)
After 14 years, I'm not the person to design a chiller plant retrofit or certify indoor air quality. I know enough about McQuay fan coil units to order parts without causing a schedule delay, but if you're doing a controls overhaul, hire a controls engineer. That's not modesty; it's the difference between a $38,000 mistake and a $380,000 mistake.
A vendor who says 'this isn't my specialty, here's who does it better' is a vendor I trust for everything else. The same principle goes for your internal decisions. Know where your expertise ends.
When should you ignore my advice? If your building has unusual code constraints, high peak hot water demand, or a heating system that predates your own job title, bring in someone who has worked on that specific setup. If your McQuay thermostat wiring is older than the technician, call the manufacturer rep and an electrician before ordering anything. If you're in a cold climate with cheap natural gas, the tankless math changes. For a large warehouse, portable equipment isn't even a short-term answer.
But for the most common scenario — an older commercial building with a few McQuay fan coil units, a damp corner, and a water heater at the end of its life — the answer is usually simple: verify compatibility, fix the root cause, and choose the heat pump water heater if you have the space. The $38,000 in mistakes I made to learn that will have to be worth something.
