Repair or replace is one of the most expensive questions a facility team answers, and it is still often settled with a rule of thumb such as the 50% rule. That shortcut ignores timing, energy use, failure risk and the value of what a new asset keeps delivering after the comparison period ends. Net present value analysis puts every cost and benefit on the same time footing, so a chiller, boiler or air handler can be judged on its full financial effect. The model below shows the formula, how to pick a discount rate, and a worked facility example, using records from a CMMS as inputs.
Equipment Net Present Value (NPV) Decision Model
Compare repair and replacement on equal terms. Discount future costs to today, include energy and failure risk, and let the numbers show which path costs less over the horizon you choose.
Why the 50% Rule Falls Short for Facility Assets
The 50% rule says to replace an asset when a repair costs more than half the price of a new one. It is quick, but it looks at one repair in isolation and ignores everything that happens after it.
| Question | 50% Rule | NPV Model |
|---|---|---|
| Does it include timing of cash flows? | No, all dollars are treated as equal | Yes, future costs are discounted to present value |
| Does it count energy and operating cost? | No | Yes, as annual cash flows on each path |
| Does it reflect rising failure cost? | Only the current repair quote | Yes, projected corrective cost by year |
| Does it value remaining life after replacement? | No | Yes, through residual value or a longer horizon |
| Does it handle downtime and risk? | No | Yes, as expected cost of failure and disruption |
| Can finance audit it? | Hard to defend the threshold | Yes, every input is visible and testable |
The NPV Formula in Plain Terms
NPV adds up all the cash flows for an option, each reduced by how far in the future it falls. For a repair or replace decision you usually compare the present value of costs, so the lower figure wins.
Cash Flow Inputs: What to Include and What Gets Missed
A model is only as good as its inputs. Most distorted decisions leave out the same few items, so check the three lists below before running any numbers.
Outflows on both paths
- Repair quote or replacement installed cost
- Planned maintenance labor and parts
- Corrective maintenance by year
- Energy and utility cost
- Controls and integration work
Inflows and avoided costs
- Energy savings from higher efficiency
- Avoided emergency call-outs
- Incentives or rebates where available
- Avoided refrigerant or compliance cost
- Salvage or trade-in value
Frequently missed
- Expected cost of failure and downtime
- Temporary cooling or heating during outages
- Disposal and removal cost
- Staff time for project management
- Remaining life after the horizon ends
Choosing a Discount Rate for Facility Decisions
The discount rate is the most debated input, and it matters. Use one rate consistently across options, state it openly, and test the result at a higher and a lower rate.
| Rate Basis | Typical Use | Strength | Caution |
|---|---|---|---|
| Organization hurdle rate | Corporate owners and REITs with a set capital approval rate | Matches how other capital projects are judged | May be too high for low-risk building systems |
| Weighted cost of capital | Owners who finance through a mix of debt and equity | Reflects the real cost of funding | Needs finance input to calculate correctly |
| Cost of borrowing | Projects funded by a loan or bond | Simple and easy to verify | Ignores equity cost and project risk |
| Prescribed public rate | Government and institutional owners | Consistent and defensible in reviews | May not reflect current market conditions |
| Real rate with constant dollars | Long-life assets when inflation is uncertain | Avoids forecasting inflation on every input | All cash flows must be in constant dollars |
Worked Example: A Chiller Repair Versus Replacement
All figures are illustrative assumptions for demonstration, not benchmarks. The comparison uses a five-year horizon and an 8% discount rate. Annual repair-path costs combine maintenance, energy and expected failure cost.
| Year | Discount Factor | Repair Cash Outflow | Repair PV | Replace Cash Outflow | Replace PV |
|---|---|---|---|---|---|
| 0 | 1.0000 | $40,000 | $40,000 | $180,000 | $180,000 |
| 1 | 0.9259 | $45,000 | $41,667 | $14,000 | $12,963 |
| 2 | 0.8573 | $55,000 | $47,154 | $14,000 | $12,003 |
| 3 | 0.7938 | $65,000 | $51,599 | $14,000 | $11,114 |
| 4 | 0.7350 | $75,000 | $55,127 | $14,000 | $10,290 |
| 5 | 0.6806 | $85,000 | $57,849 | $14,000 | $9,528 |
| 5 residual | 0.6806 | $0 | $0 | minus $30,000 | minus $20,417 |
| Total PV of cost | $293,396 | $215,481 |
Feed the Model With Real Maintenance History
The Horizon Problem: Comparing Options With Different Lives
A repair may extend life by three years while a new unit lasts twenty. Comparing total cost over different lifespans favors the shorter option unless you correct for it.
Option 1: Common horizon
Option 2: Equivalent annual cost
Option 3: Repeat the cycle
Sensitivity Testing: Stress the Assumptions Before You Present
Decision makers trust a model that shows how it behaves under pressure. Change one input at a time and record whether the preferred option flips.
| Input to Test | Range to Try | What a Flip Would Tell You |
|---|---|---|
| Discount rate | Several points above and below the base rate | Whether the choice depends on how heavily future cost is weighted |
| Repair path cost growth | Slower and faster growth than your trend | Whether the case rests on a forecast of rising failures |
| Energy price | Lower and higher utility cost per unit | How much of the benefit comes from efficiency gains |
| Failure and downtime cost | Conservative and full disruption estimate | Whether risk exposure alone justifies the decision |
| Replacement price | Quote tolerance and scope changes | How much budget room exists before the case reverses |
| Horizon length | Shorter and longer analysis periods | Whether residual value assumptions are carrying the result |
A Six-Step Decision Workflow for Repair or Replace
Use the same sequence for every candidate asset so results are comparable across the portfolio and the capital plan stays consistent. Assign one owner to each step, keep the assumptions in a shared record, and schedule a review date so the decision is revisited if prices, energy rates or failure patterns move materially.
Turning Failure Risk Into an Annual Cash Flow
Failure risk is the input most often left as a vague worry. Convert it into expected cost by multiplying the chance of each failure type by its full consequence, then place the total on the repair path for each year.
| Failure Type | Assumed Annual Probability | Full Consequence | Expected Annual Cost |
|---|---|---|---|
| Minor failure, same-day repair | 40% | $8,000 in labor, parts and call-out | $3,200 |
| Major failure, rental and extended outage | 15% | $60,000 including rental and disruption | $9,000 |
| Total expected failure cost | $12,200 per year |
Beyond the Numbers: Factors That Sit Beside NPV
NPV answers the financial question. Some decisions also turn on constraints that a cash flow model captures poorly, so document them next to the result.
Compliance and safety
Operational continuity
Capital availability
Common NPV Mistakes in Facility Equipment Decisions
A tidy spreadsheet can still mislead. These errors appear repeatedly in repair versus replace analyses and are worth checking before any decision is presented.
Where the NPV Inputs Come From in Oxmaint
Most NPV inputs already exist in maintenance records. Oxmaint helps facility teams keep them organized so the model can be rebuilt quickly whenever a repair quote arrives. Because the records are structured by asset, a planner can refresh the cost history, update the failure counts and rerun the comparison in a single sitting instead of rebuilding a spreadsheet from scratch. That speed matters when a contractor quote has an expiry date and the capital committee meets next week.
| NPV Input | Oxmaint Capability | How It Helps |
|---|---|---|
| Cost of past repairs | Work orders and asset history | Shows corrective spend and its trend for each asset |
| Failure frequency | Corrective maintenance records | Supports a defensible failure and downtime forecast |
| Planned maintenance cost | Preventive maintenance schedules | Gives the baseline annual cost of keeping the asset running |
| Parts and consumables | Inventory | Identifies parts cost and availability risk on aging units |
| Portfolio comparison | Reporting and dashboards | Ranks assets by cost trend to prioritize NPV reviews |
Presenting an NPV Result to a Capital Committee
A correct model still needs a clear story. Structure the presentation so reviewers can follow the logic and challenge the inputs that matter most.
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