I've handled HVAC service orders for ten years. In that time, I've personally made (and documented) six significant mistakes—totaling roughly $40,000 in wasted budget. These days I maintain our team's checklist so other people don't repeat my errors.
The question I get most often is simple: old McQuay water source heat pump just failed—repair or replace? Everyone focuses on the repair quote and the replacement quote. Almost nobody talks about total cost of ownership.
So here's a comparison based on the mistakes I've made, the manuals I've used, and the two times I wish I had planned better.
What I'm Comparing: Total Cost, Not Sticker Price
The price on the invoice is just the beginning. What I mean is: total cost of ownership includes the upfront quote, plus downtime, risk, energy, maintenance, and the chance of doing it twice.
When I compare keeping an old McQuay water source heat pump versus replacing it, I look at four dimensions:
- Upfront cost
- Reliability and risk
- Energy and operating cost
- Maintenance and the "while you're in there" work
If a vendor wants to talk only about the purchase price, that's a red flag.
Dimension 1: Upfront Cost
Repair with an old manual can look almost embarrassingly cheap. In May 2024, I helped a building owner fix a 20-year-old McQuay WSHP for $240—$40 for a 24V solenoid valve and $200 labor. The old McQuay water source heat pump manual made it a 40-minute diagnosis.
But in 2023, I saw the same type of repair turn into $2,800 because nobody had the manual. No manual means the technician traces wiring, guesses at labels, and orders parts by trial and error. That's the "cheap repair" that quietly eats the replacement budget.
Replacement quote? For a similar size heat pump, plan on five figures by the time you add crane, refrigerant, piping, controls, and disposal of the old unit. I want to say $12,000–$18,000 as of early 2025, but don't quote me on that—prices vary by region, and you should get current quotes.
So on sticker price, repair with a good manual usually wins. But the next three dimensions are where the decision can flip.
Dimension 2: Reliability and Risk
Here's what surprised me when I started actually tracking failures: a repaired old unit can be more reliable than a rushed new installation. In 2022, I watched a brand-new heat pump fail within three months because the installers didn't purge the lines properly. The old McQuay unit it replaced had never leaked a drop of refrigerant.
But the risk also goes the other way. If the compressor is already weak, or the water coil is corroded, no manual is going to save you. You're betting against the unit's age.
I remember a 30-ton McQuay centrifugal chiller in a medical office building. We found what looked like the original manual, but the chiller had been retrofitted with a VFD and a new control panel that weren't in the book. If I hadn't verified the actual wiring before ordering parts, we would have spent about $1,400 on the wrong contactors. I learned to treat every old manual as "accurate until proven otherwise."
Conclusion: old and new carry different risk profiles. New equipment has a warranty; old equipment has history. Both can fail in surprising ways, so the answer depends on the actual unit and the actual install crew.
Dimension 3: Energy and Operating Cost
Yes, newer equipment is generally more efficient. But "generally" is doing a lot of work. If a heat pump runs 3,000 hours a year, even a 10% efficiency difference can change the TCO by thousands. If it runs 200 hours a year as backup, you'll never make back the replacement cost.
Before swapping anything, look at the actual run hours and the meter. ASHRAE Guideline 14 (ashrae.org) explains why savings need to be measured, not promised. AHRI's directory (ahridirectory.org) is where you can check a new unit's certified performance numbers.
I'm not saying old units are efficient. I'm saying don't replace for efficiency alone unless the run hours justify it. The cheapest decision is the one that matches actual use.
Conclusion: don't let an efficiency claim push you into a replacement unless you've done the math.
Dimension 4: Maintenance and Condenser Coils
This is where a lot of repair-vs-replace decisions actually get made. Maintenance is the largest hidden line item in the TCO.
One of the cheapest things you can do on either old or new equipment is clean the condenser coils. It sounds too simple to matter. It isn't. Dirty coils make the compressor work harder and turn a minor issue into a $100 part plus an $800 service call.
How to Clean Condenser Coils Without Learning the Hard Way
I learned this one the embarrassing way. In 2017, I skipped coil cleaning on a rooftop unit before a big seminar because I thought, "what are the odds?" The odds caught up with me. High-pressure trip shut down the AC at 10 a.m. Rentals cost $400, and the emergency service call added another $400.
Here's the routine I use now for any water source heat pump or chiller:
- Disconnect power and lockout/tagout.
- Remove access panels and tape off the fan motor if needed.
- Spray a pH-neutral coil cleaner on the coil.
- Rinse from the inside out—that's where the fins collect the most junk.
- Straighten bent fins with a fin comb.
- Let everything dry completely before restarting.
If you have the old McQuay water source heat pump manual, check the maintenance schedule. I've found original manuals list fan motor lubrication, water flow checks, and other small tasks that today's "check-and-change" mindset skips.
Conclusion: clean the coils before you make any major decision. It's cheap, it's fast, and it might buy you another season.
Wait—But What About Outdoor Heaters and Tankless Hot Water Heaters?
I get this question after people hear "heat pump." They immediately start thinking about every other heating device. That's valid, but it's also a TCO trap.
An outdoor heater is for a specific use: spot heating outside or in uninsulated spaces like loading docks, patios, or garage entrances. It's not a replacement for a 5-ton water source heat pump heating a whole office. I've seen a team try to "replace" a heat pump with a row of patio heaters. The energy bill went up, and the conference room stayed cold.
A tankless hot water heater is great for domestic hot water. It's not a space heating solution. If someone tries to size a tankless unit for baseboard heat or radiant slab heat, the math gets messy fast.
The TCO lesson: compare options that actually serve the same load. If you're heating a loading dock, an outdoor heater makes sense. If you're heating a conference room, you're still in heat pump or chiller territory. For a large chilled water system, the relevant comparison probably involves a McQuay centrifugal chiller, not a water heater.
Conclusion: use the right tool for the right load, or you'll pay twice.
So, Repair or Replace?
Here's my decision guide, after more mistakes than I'd like to admit.
Keep the old McQuay and repair it if:
- You have the old McQuay water source heat pump manual—and the wiring matches.
- The compressor and water coil are healthy.
- Parts are available (or you know what can be substituted safely).
- The repair cost is less than roughly half the cost of a replacement, and you don't plan to stay in the building more than five years.
Replace it if:
- The manual is missing or contradicts what you see in the panel. That's a red flag, not a challenge.
- The compressor is shot or the coil is leaking.
- You're adding significant load, and the old unit is already near capacity.
- You need a warranty for regulatory or financing reasons.
And before any of that, go clean the condenser coils. Put that on the checklist first. If I'd done it in 2017, I could have saved $800 and the privilege of being the guy who shut down the seminar.
If you're on the fence between repair and replacement, calculate the total cost of ownership over your expected time in the building. Get actual run hours, get part quotes, and get a commissioning quote for the new unit. The lowest sticker price is rarely the lowest TCO. That's the lesson I keep having to re-learn, and I'm putting it in writing so maybe you won't have to.
