Mean time to failure
Mean time to failure (MTTF) is the average amount of time a piece of equipment runs before it fails, calculated by dividing total operating hours across a fleet or asset class by the number of failures recorded in that period.
The inputs.
- Total operating hoursRun hours (or run-days) across the fleet or asset class for the period — the denominator that turns failures into a rate.
- Number of failuresFailures recorded in the same period. Requires a consistent definition of what counts as a failure versus routine wear.
- Applies toAssets you replace rather than repair down to the component level. For units you rebuild and return to service, mean time to repair is the closer-fitting number.
How to read MTTF.
How to calculate mean time to failure
MTTF equals total operating hours (or run-days) for a group of assets divided by the number of failures those assets recorded over the same period. It applies to assets you replace rather than repair down to the component level; for equipment you rebuild and return to service, mean time between failures (MTBF) is the closer-fitting number. Either way, the calculation is only as good as the underlying data — you need reliable install dates, run hours or service dates, and a consistent definition of what counts as a failure versus routine wear.
Why MTTF matters for commercial contractors
On a 10-to-200-tech commercial or mechanical book of business, MTTF turns anecdote into a plannable number: which rooftop units, chillers, or compressor classes are approaching end of reliable life, and which customer sites carry the highest failure risk. That feeds two decisions directly — when to recommend replacement instead of another repair, and how to price or renew a service agreement on aging equipment before it becomes a loss leader.
What's a good MTTF benchmark
There isn't a single defensible number — MTTF varies by equipment class, age, run hours, duty cycle, and climate, so treat any published figure as general guidance rather than a target to hit. What matters more than the absolute value is the trend: is MTTF for a given equipment class or manufacturer shrinking site over site, or holding steady against your PM cadence.
How Thermal tracks MTTF automatically
Because equipment is a first-class record in Thermal — not a free-text field on a work order — every install date, repair, and failure against a given unit rolls up automatically into its service history. MTTF calculates directly from that timeline instead of a spreadsheet someone has to maintain, and it stays current as new work orders close, independent of accounting-system sync status. QuickBooks Online sync is in early access; the Sage Intacct and Business Central adapters are on the roadmap.
Questions attached to this term.
What's the difference between MTTF and MTBF?
MTTF (mean time to failure) is for non-repairable assets you replace outright. MTBF (mean time between failures) is for repairable assets you fix and return to service, measuring the interval between successive failures on the same unit.
Does MTTF apply to HVAC and mechanical equipment?
Yes. It's commonly tracked at the component level — compressors, motors, control boards — as well as at the whole-unit level for rooftop units, chillers, and boilers, especially across multi-site commercial accounts.
How much service history do I need before MTTF is meaningful?
A handful of failures per equipment class gives a rough signal; the number gets more reliable as your equipment database and service history grow, which is why contractors coming off spreadsheets or a legacy system often see MTTF sharpen over the first few quarters on a new platform.
Can MTTF replace a preventive maintenance schedule?
No — MTTF informs replacement and pricing decisions, but PM schedules and compliance tracking are still what prevents the failure in the first place. The two are complementary, not substitutes.
These numbers, on your own book.
If you want to see them calculated from real work orders and agreements rather than a spreadsheet, that's a demo.