Rooftop Unit Repair or Replace? A Guide for Twin Cities Businesses

If you own or manage a commercial building in the Twin Cities, there’s a good chance your heating and cooling lives on the roof. Rooftop units heat and cool everything from strip-mall storefronts and office suites to restaurants, churches, and light industrial spaces. They’re out of sight right up until one stops working — usually on the hottest afternoon in July or during a January cold snap when the store is full of customers or the office is full of staff.

When a technician tells you a unit has a major problem, you’re suddenly facing a real decision: fix it again, or replace it? There isn’t a single rule that answers that for every building, but there is a consistent set of factors we look at. Here’s how we think it through with the business owners and property managers we work with.

What a rooftop unit is (and why it matters for the decision)

A rooftop unit, or RTU, is a packaged HVAC system — everything in one cabinet. Most units in our area include a compressor and condenser coil for cooling, an evaporator coil, a supply fan, filters, controls, and a gas-fired heating section with burners and a heat exchanger. Some newer units are heat pumps or have electric heat. Many also include an economizer, a set of dampers that can bring in cool outdoor air for “free cooling” when the weather allows, instead of running the compressor.

The unit sits on a roof curb — a raised, insulated frame fastened and flashed into the roof — with supply and return ductwork dropping down through the curb into the building. That curb, the roof around it, and the crane needed to lift a unit up there all come into play when you’re deciding whether to replace. Our rooftop units page gives an overview of what we service and install.

How long rooftop units typically last

ASHRAE’s equipment service-life data lists a median life of around 15 years for rooftop units, and in practice we generally see well-maintained units lasting somewhere in the 15-to-20-year range. Units that were poorly maintained, undersized, or run hard in demanding applications like restaurant kitchens can wear out sooner. Units with consistent maintenance and a light duty cycle sometimes go longer.

Age alone doesn’t decide anything, but it sets the context. A major failure on a five-year-old unit is almost always a repair. The same failure on an 18-year-old unit is a very different conversation.

The big failures that force the question

Most RTU service calls are for things like failed motors, capacitors, contactors, igniters, belts, sensors, or control boards. Those are normal repairs on any unit, and at almost any age they’re worth doing. The repair-or-replace question usually comes up with one of a handful of expensive failures.

A failed compressor is the most common one. It’s the most expensive single component in the cooling section, and the repair involves recovering refrigerant, replacing the compressor, and often a filter-drier and other parts. On an older unit, you also have to ask whether a new compressor is being bolted onto coils and controls that are near the end of their own lives.

A cracked or failed heat exchanger in a gas-fired RTU is the other big one, and in Minnesota it’s more common than people expect because these units run hard for so much of the year. The heat exchanger keeps combustion gases separated from the air that goes into your building. A crack is a safety issue, not just a comfort issue, and a unit with a failed heat exchanger should not be run for heat. Replacement heat exchangers aren’t always available for older models, and when they are, the labor to install one on a rooftop can make replacement the better value.

Other expensive failures include badly corroded or leaking coils, a failed supply fan motor on a direct-drive or variable-speed unit, and control failures on older units where the original parts are no longer made.

Refrigerant, efficiency, and parts availability

Refrigerant type matters more now than it did a few years ago. Units old enough to use R-22 rely on refrigerant that’s no longer produced, so a leak or compressor failure on an R-22 unit is usually the point to replace. Units using R-410A can still be serviced, but under the EPA’s refrigerant transition, new packaged equipment has moved to lower-GWP refrigerants, and R-410A supply is being stepped down over time. That makes large refrigerant repairs on older R-410A units a less attractive long-term bet. (For the homeowner side of this change, see our post on the new AC refrigerant.)

Efficiency is the other half of the equation. A new unit will almost always use less energy than a unit from 15 or 20 years ago, and features like multi-stage or variable-speed compressors and fans, better controls, and properly working economizers can make a real difference in operating costs. The savings rarely justify replacing a healthy unit on their own, but they absolutely belong in the math when you’re considering a big repair on an old one.

Parts availability is the quiet factor. On older units, a failed control board or proprietary component can mean long lead times or a used part — and days of downtime while you wait.

What replacement really involves: curbs, cranes, and downtime

Replacing an RTU isn’t just a swap. Each of these needs to be planned before you commit.

• Curb fit. New units don’t always match the footprint of the old curb. If they don’t, a curb adapter — a fabricated transition piece — may be needed to connect the new unit to the existing curb and ductwork. Having our own sheet metal shop lets us build adapters and transitions to fit.
• Crane lift. Most RTU replacements need a crane to lift the old unit off and set the new one. That means scheduling, a clear area to stage the crane, and sometimes a street or parking-lot closure.
• Roof condition. The roof around the curb has to be sealed properly afterward. If the roof itself is near the end of its life, coordinating the RTU replacement with roofing work can save you from disturbing the same area twice.
• Structural and electrical. If the new unit is heavier, or if you’re changing capacity or type, the roof structure and the electrical service to the unit need to be confirmed. Changing capacity also affects gas piping and the building’s mechanical permit.
• Downtime. A straightforward like-for-like replacement can often be done in a day of disruption, but you’ll want to plan around your business hours and what the space can tolerate without heating or cooling.

Minnesota-specific issues on the roof

Our climate is hard on rooftop equipment. The heating section works for most of the year, and a unit that’s undersized or struggling shows it on design days when it’s well below zero. Heat exchangers go through a lot of heating and cooling cycles over a long season, which is part of why we pay close attention to them.

Snow and drifting create their own problems. Drifts can bury unit intakes, block condenser coils, and pack snow into outdoor air openings. Snow shoveled or plowed off the roof near a unit can do the same. Units should have clear access paths and room around them, and it’s worth checking after a big storm.

Freeze protection matters too. Units that bring in a lot of outdoor air, or economizers stuck open, can pull subzero air across coils and cause freeze-ups, nuisance trips, or cold drafts inside. Low-limit controls and properly working dampers and actuators prevent a lot of those calls.

Restaurants and commercial kitchens have an extra piece to consider: make-up air. Kitchen exhaust hoods pull large volumes of air out of the building, and that air has to be replaced — heated, in our winters — or the building goes negative, doors are hard to open, and hoods and appliance venting don’t perform correctly. If you’re replacing an RTU in a restaurant, it’s the right time to look at whether your make-up air and RTUs are working together.

Plan replacement before it’s an emergency

The worst time to replace a rooftop unit is after it fails at peak season. Equipment might not be in stock, crane schedules are tighter, and you’re paying for downtime while you wait. If you have units that are older, have needed major repairs, or are on R-22, it’s worth getting them assessed and budgeted before they fail.

Spring and fall are generally the easiest times to replace RTUs in Minnesota. Weather is milder, the building can tolerate some time without heating or cooling, and scheduling is more flexible. For buildings with several units, replacing them in phases over a couple of years is often easier on budgets than waiting for a cluster of failures. We can help with full retrofit planning when a building needs more than one piece of equipment updated.

After a replacement or retrofit, testing and balancing confirms that each space is getting the airflow it was designed for. It’s often overlooked, but it’s how you make sure the new equipment actually delivers what you paid for.

Utility rebates for business equipment

Both Xcel Energy and CenterPoint Energy run business energy-efficiency rebate programs in Minnesota that can cover qualifying high-efficiency HVAC equipment and related controls. Qualifying equipment, rebate amounts, and application rules change from year to year, and some programs have deadlines or require paperwork with dated invoices and proof of installation. Check current program rules before you buy, and plan the paperwork into the project.

Maintenance that extends RTU life

Most RTUs that die early do so because they were neglected. A good preventive maintenance program usually includes filter changes on a regular schedule, belt inspection and replacement, coil cleaning, checking refrigerant operating pressures, inspecting the heat exchanger and burners, verifying economizer operation, testing safety controls, and checking electrical connections. Many buildings do a cooling-focused visit in spring and a heating-focused visit in fall.

Maintenance also gives you a paper trail and early warning. When a technician can tell you a unit’s compressor is running hot or its heat exchanger is showing wear, you can plan and budget, not scramble.

Getting a clear answer for your building

If a rooftop unit at your property needs a major repair, or you’re trying to plan the next few years of equipment spending, we can inspect the units, give you straight information on condition and remaining life, and quote both the repair and a replacement so you can compare them side by side.

Heating & Cooling Two has served Twin Cities businesses since 1980, with NATE-certified technicians and our own sheet metal shop for curbs, adapters, and ductwork. Learn more about our commercial HVAC services, or call 763-428-3677 to schedule service or an estimate.