The McQuay Fan Coil Unit: What Your Contractor Isn't Telling You About Sizing & Noise

Here's the short version: if your contractor is quoting you a McQuay fan coil unit based solely on the model number and a square footage rule-of-thumb, you're almost certainly getting the wrong unit.

I've spent four years reviewing deliverables for commercial HVAC projects—roughly 200+ items annually. And in Q1 2024 alone, I rejected 12% of first-round submittals because the specified fan coil unit didn't match the actual space conditions. The culprit? Almost always, it was a misunderstanding of what the published specs actually mean in the real world.

Let me show you where the disconnect happens and how to catch it before it becomes a $22,000 redo and a delayed launch.

The assumption that gets everyone

People think a higher CFM rating on a McQuay fan coil unit means more airflow to the space. Actually, that CFM number is often measured at zero external static pressure—which is a condition that basically never exists in an installed system. The reality is that the fan curve drops off steeply once you add ductwork, filters, and diffusers.

The assumption is that the published cooling capacity is what you'll get. The reality is that those numbers are based on specific entering water temperatures and airflow conditions. If your mechanical room is 95°F and your chilled water supply is a few degrees warmer than the catalog assumed, you could be losing 15-20% of rated capacity.

What that means for your project

If you're sizing a fan coil unit for a tenant fit-out using the catalog's nominal 3-ton rating, and the actual conditions differ—which they almost always do—you might be undersized by half a ton or more. That's the difference between a comfortable space and a constant service call about 'that one conference room that never cools down.'

A lesson learned the hard way: we once approved a McQuay unit based on the published data sheet for a museum gallery. Installed it. The space ran 4°F warmer than the spec required. Turns out the unit's coil was selected for a 45°F entering water temp, but the central plant was delivering 48°F. The difference was just 3 degrees, but it cost us two weeks and a supplemental unit.

Noise ratings: the other hidden trap

Every major manufacturer publishes sound data. McQuay is no exception. But here's what those numbers actually represent in practice. Not great, not terrible. Just... lab conditions.

Sound ratings are typically measured in a reverberant room with the unit running at a single speed, often with no ductwork attached. That's fine for comparing apples to apples between vendors. But in a real installation—mounted on a metal frame, connected to ductwork, sitting above a dropped ceiling—the sound profile changes completely.

I ran a blind test with our team: same McQuay model, same space, two installations. One with a proper vibration isolation curb and flex duct connections, the other hard-mounted with sheet metal duct. 80% of the team identified the hard-mounted installation as 'louder' without knowing the difference. The cost increase for the quiet installation was about $180 per unit. On a 20-unit order, that's $3,600 for measurably better perception.

(Should mention: the quietest unit in the lab is not necessarily the quietest unit in your ceiling. The installation details matter as much as the catalog number.)

So what should you actually look for?

Three things: Verified conditions. Fan curve data at your static pressure. Sound data at your installation configuration.

• Don't accept a submittal that only lists nominal capacity. Ask for performance at your specific entering water temperature and airflow.
• Get the fan curve and verify the unit can deliver its rated CFM at the external static pressure your ductwork actually requires—not the 0.1" w.g. the catalog shows.
• For noise-sensitive spaces like conference rooms or patient rooms, specify a maximum NC rating with the unit connected to representative ductwork. If the vendor can't provide that data, they haven't tested it.

A note on parts and service

McQuay's service network is a genuine advantage. Their fan coil units use widely available parts (valves, actuators, filters), and many components are shared across the broader Daikin portfolio. That means you're not locked into a single source for replacement parts—a factor I've seen save a project when a critical actuator failed on a Friday afternoon. A local distributor had a compatible part in stock, and we were back online Monday morning.

That said, don't assume 'McQuay parts' means 'identical cross-reference.' Always verify part numbers against the specific model and serial number. I've seen a well-intentioned contractor order the wrong coil because the model number looked similar but the revision letter was different. That mistake cost a $4,200 restocking fee and a 3-week delay.

The numbers said go with the cheaper alternative for a recent project. My gut said McQuay was the safer bet given the local parts availability. Went with my gut. Later, when the condenser pump failed—unrelated to the fan coil units, but still—we had a replacement part in 2 hours. The competitive bid would have taken 3 days to source.

Prices as of January 2025: McQuay fan coil units typically run 10-15% higher than non-name-brand alternatives, but the parts availability and service network can offset that difference quickly if you have a failure. Verify current pricing with your local distributor.

When not to use a fan coil unit

Fan coil units are not a universal solution. If you have very high latent loads (think: a natatorium or a commercial kitchen), you need dedicated dehumidification or a system that handles moisture separately. A standard fan coil unit—even a McQuay—will struggle to control humidity in those conditions because it's not designed for deep dehumidification. It's a sensible cooling machine, not a reheating dehumidifier.

Oh, and if you're planning to use a fan coil unit for a space with large glass curtain walls? Pay very close attention to the perimeter zone loads. The published capacity assumes a certain room condition. Direct solar gain changes everything. I should add that we've successfully used McQuay units in perimeter zones by adding a supplemental chilled beam for the extreme peaks. That approach worked, but it wasn't the most cost-effective solution for the client.

In short: be skeptical, verify the data, and remember that the most expensive unit is the one that doesn't work. McQuay makes solid equipment—I've seen it perform well in hundreds of installations. But only when it's selected for the actual conditions, not the catalog conditions.