Generator Buying Checklist: A Cost Controller's Guide to Total Cost of Ownership

If you are responsible for buying a backup generator—whether it is an 80 kVA Perkins generator for a facility or a whole-house unit for your own home—don't start with the price tag. Start with total cost of ownership.

I have been a procurement manager at a mid-sized equipment manufacturer for 7 years. I manage roughly $180,000 a year in emergency power spend—fuel, maintenance, and replacement equipment. I have compared 11 generator vendors, not counting the one that just mailed a brochure. This is the 7-step checklist I use.

Step 1: Define the load profile before you call anyone

Generators are rated in kVA and kW. If you are looking at an 80 kVA Perkins generator, that is about 64 kW at 0.8 power factor. Buy too close to your load and you will trip the main before the backup even proves useful.

The first thing I ask for is a breakdown of what has to run on generator power. Is it one pump, a few lights, or an entire production line? What are the starting surge loads? A motor can surge to 300% of its running power for a few seconds. That changes the size you need.

This is also where you decide between standby and prime rating. A standby-rated generator is meant to carry the load for a limited number of hours per year. A prime-rated unit can run longer, and the price difference is real.

I should add: get this in writing from whoever owns the load. The building engineer's 'probably enough' is not a specification.

Step 2: Build a TCO spreadsheet, not a quote comparison

It doesn't take a finance degree to know that a $15,000 generator with a $14,000 install costs more than an $18,000 generator with a $6,000 install. But you need to see it on paper.

My spreadsheet has line items: base unit, alternator, controls, transfer switch, fuel tank, concrete pad, exhaust, remote monitoring, freight, permits, commissioning, load bank test, first-year service. When I put two quotes for the same 80 kVA Perkins generator side by side, the lower one was missing almost all of those. It basically was a bare iron engine and a generator head.

The surprise wasn't the sticker price. It was the $4,000 in extras that the lower quote didn't include. That is the contrast that turned me into a TCO person.

The TCO table is also a negotiation tool. If a vendor says their generator is cheaper, ask them to fill in every line where their quote has a blank. That stops the 'free setup' trick.

Step 3: Size the transfer switch right

The transfer switch is probably the most under-budgeted part of any generator project. For a residential generator installation, a 200-amp automatic transfer switch can run $1,500 to $5,000 installed, depending on panel age and code requirements. In commercial work, the transfer switch often costs more than the generator.

Don't reuse an old switch that didn't pass your load calculation. In Q2 2024, we changed a 600-amp switch and it took five hours after the unit was delivered. Actually, that was a different project. The point is: plan the switch at the same time you plan the generator.

Step 4: Run the numbers on fuel

Fuel is a recurring cost that surprises people. A 100 kW diesel commercial generator burns roughly 7 or 8 gallons per hour at 75% load. If you run it for an 8-hour outage at $3.50/gal, that is close to $200 for one day. Over a winter with several outages, it adds up.

For a whole-house generator, fuel type is a total-cost decision too. Propane tanks need refilling, natural gas needs pipe capacity, and diesel needs delivery and storage. At least, that's been my experience with commercial diesel units.

Don't forget partial-load efficiency either. The best fuel economy is usually around 70-80% load. A generator idling at 20% load burns more per useful kWh.

Oh, and if the site has an existing diesel tank, test the fuel before relying on it. Old fuel is a classic generator failure mode.

Step 5: Compare service networks, not just brand names

In the residential world, people ask about Kohler vs Generac whole house generator. Honestly, both brands make good units. Generac has a wider dealer footprint, and Kohler's commercial heritage can make parts easier to source in some regions. But the brand is not the emergency plan. The question is whether someone will show up within 24 hours when it fails.

You may also see a Honeywell backup generator in your search. Private-labeling is common in this segment, so ask the dealer who actually manufactures the unit and where the closest service center is. Same idea applies on the commercial side: Perkins generator models are packaged by different manufacturers, and the local dealer's track record matters as much as the engine badge.

The brand choice is not a no-brainer. The service contract is what makes or breaks you in an outage.

Step 6: Put code, emissions, and sound into the budget

I used to think permits and sound were the electrical contractor's problem. Then we had to buy a larger muffler after the fact because the original one was too loud for a property line requirement. It wasn't huge, but it was avoidable.

For commercial systems, NFPA 110 sets testing requirements for emergency power supply systems. Level 1 systems often need monthly loaded exercises plus an annual load bank test. The annual load bank test is the step most people ignore. It is not optional in many facilities, and skipping it can void the warranty. Budget for it from day one.

For residential generator installation, local noise limits, setback rules, and fuel storage restrictions matter. A 22kW air-cooled unit is not silent. If the permit says 60 dB at the property line, you need to know that before you pour the pad.

For commercial diesel units, emissions rules like EPA Tier 4 affect engine selection. A Tier 4 compliant 80 kVA Perkins generator will cost more than a non-compliant one, but it might be the only option allowed in your county.

Cold weather matters too. In northern sites, budget for block heaters and battery warmers.

Step 7: Negotiate the full contract, not the machine

The last step is to make sure everything above appears in the purchase agreement. Commissioning, load bank test, operator training, remote send/stop, warranty labor, spare parts. If a vendor avoids including start-up and testing, that is a red flag. If they won't give a schedule for warranty responses, that is a deal-breaker for me.

Before final payment, I want to see the unit start, transfer, carry the load, and shut down in sequence. We do this with the utility and the transfer switch together. It takes four hours, but it has caught more wiring problems than I want to remember.

And one more thing: for a residential project, get at least three itemized quotes. The difference in installation costs is bigger than the difference in generator prices, and the lowest bid is rarely the lowest total cost.

Bottom line

A generator is a system, not an appliance. The engine is only the beginning. The transfer switch, fuel supply, installation, testing, and service contract are where the real cost lives.

Use this checklist for a 20kW home standby, a 100kW commercial unit, or an 80 kVA Perkins generator. The price tag is just the entry ticket; the total cost is the full bill.