GeneratorSizer

5-year ownership cost

Updated October 3, 2026.

Built by Jeremy Panasuk.

Use this when you already know a running load and you want five-year cash, not a watt class. The classes themselves are on portable vs standby. Every dollar field on this form is an input you type. The defaults are not a price index.

What the button adds

GS.tco in assets/lab.js always uses 5 years. It does not read a years field.

EIA lists 120,214 Btu per gallon of motor gasoline. That heat content is not a price, and it is not the ÷ 7,000 rule. Kilowatt-hours, which are a different unit, are on the kW to kWh calculator.

Worked clicks

The form opens at 2,210 running watts, 18 outage hours per year, $3.40 per gallon, a $1,400 portable, a $12,500 standby install, and $280 a year of service. The oil schedule is Honda EU2200i. The oil-cost box is blank. 2,210 W is the sequencer’s stored well-ranch always-on running sum, described on the sequencer page. The dollar figures are whatever is in the boxes.

Type 12 in “Your cost per oil change” and leave the other boxes, including Honda. That 12 is a cost you typed. It is not a quoted oil price. Ten changes × $12 = $120. Portable = 1,400 + (2,210 / 7,000 × 18 × 3.40 × 5) + 120 = $1,616.61, shown as $1,617. Standby stays $13,900. Break-even stays 10,341.

Second click: with 12 still in the oil-cost box and Honda still selected, change only the outage hours to 120. Annual fuel becomes 2,210 / 7,000 × 120 × 3.40 = $128.81, shown as $129. Five-year engine hours = 600, which is 10 hours per month. The first month still comes before 20 hours, and 6 months (60 hours) still comes before 100 hours, so Honda still counts 10 changes and $120 of oil. Portable = 1,400 + (2,210 / 7,000 × 120 × 3.40 × 5) + 120 = $2,164.06, shown as $2,164. Standby stays $13,900. Break-even stays 10,341 hours, because that line does not use the 120. Six hundred hours is still far under 10,341. The runbook is where those 120 hours become cans.

Third click: set the outage hours back to 18, leave 12 in the oil-cost box, and switch the schedule to Generac GP6500 / GP8000E. The first change is hour 30, which is month 20 at 1.5 hours per month. After that, 12 months (18 hours) comes before 100 hours, so the changes are months 20, 32, 44, and 56. That is 4 changes × $12 = $48. Portable = 1,400 + (2,210 / 7,000 × 18 × 3.40 × 5) + 48 = $1,544.61, shown as $1,545. At 120 hours per year on the same Generac schedule the first change is month 3, and then every 100 hours (10 months) comes before 12 months: hours 30, 130, 230, 330, 430, and 530, which is 6 changes × $12 = $72. Portable = 1,400 + (2,210 / 7,000 × 120 × 3.40 × 5) + 72 = $2,116.06, shown as $2,116. Set the outage hours to 0 with 12 still in the oil-cost box. Generac counts 0 changes, because the first change is the 30-hour mark and the yearly clock starts after it, so oil dollars are $0 and the portable total is the $1,400 purchase. Honda at zero engine hours still counts 10, because the first month and every 6 months still arrive: $120 of oil, portable total $1,520. Annual fuel on that click is $0. Break-even stays 10,341.

Limits and a common mistake

Reading 10,341 as “hours per year” makes a standby look cheaper than this arithmetic says. The 10,341 is total portable runtime. The outage-hours box scales fuel, and it moves the oil count only when an hour limit arrives before the calendar limit. The oil-cost box is the only oil price.

The comparison leaves out labor, noise, and standby fuel. A heavier open-frame and a neighbor’s window are the lot-line question, not a dollar in this total. A load that needs a larger machine changes the purchase prices you type; the script does not look up either price. Permanent installation of a standby takes a licensed electrician and a permit where local code requires one.

Compiled with AI assistance from the sources below. Spot an error? Email [email protected].

Sources