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Smart Building ROI Calculator

Building IoT system payback from energy and maintenance savings.

About this calculator

This calculator splits a building's energy bill into an HVAC share and a lighting share, applies separate expected savings percentages to each, and adds a flat 15% reduction on top of your existing maintenance budget for predictive fault detection — that maintenance figure is hard-coded in the engine, not an input you can tune, so it applies uniformly regardless of building type. The combined energy and maintenance savings are then compared against total implementation cost (a simple $/sq ft figure covering sensors, network, and building-management-system upgrades) to produce a simple payback period, a five-year ROI, and an overall energy-reduction percentage. Simple payback here means implementation cost divided by first-year savings, with no discounting or escalation of energy prices over time, so it will understate long-run returns if utility rates rise, and it will overstate them if savings decay as sensors drift out of calibration or building operations staff stop acting on the alerts.

The 15-30% HVAC and 30-50% lighting savings ranges built into the default values reflect typical outcomes for occupancy-based control and daylight harvesting, but real results depend heavily on how outdated the existing controls are — a building already on a modern BMS will see far less upside than one still running static schedules. A payback of -1 signals the inputs produced zero or negative savings, meaning the case doesn't pencil out as configured. Because HVAC and lighting percentages of total energy are inputs rather than measured values, garbage-in-garbage-out risk is real: pulling these from an actual utility bill breakdown or ASHRAE Level 1 audit will give a far more defensible number than guessing.

Inputs

sq ft
%
%
%
%

Results

Annual savings ($)

$40,563.00

Implementation cost ($)$250,000.00
Payback period (years)6.2
5-year ROI (%)-19
Energy reduction (%)16.8
Energy savings ($/yr)$29,313.00
How to Use This Calculator
  1. Enter building size in sq ft and current annual energy cost per sq ft.
  2. Set HVAC and lighting energy shares as percentages of total energy.
  3. Enter implementation cost per sq ft and expected HVAC and lighting savings percentages.
  4. Input annual maintenance cost to capture O&M savings.
  5. Review Annual savings ($), Payback period (years), and 5-year ROI (%) to evaluate the upgrade.

How the result changes with Building size (sq ft)

Building size (sq ft)Annual savings ($)
25,000$25,906.00
37,500$33,234.00
75,000$55,219.00
125,000$84,531.00

What each input means

Building size (sq ft)
Total conditioned floor area in square feet.
Energy cost ($/sq ft/yr)
Annual energy cost per square foot. US avg office: $2.50-$4.50/sq ft.
HVAC energy share (%)
HVAC as percentage of total energy. Offices: 35-45%, warehouses: 15-25%.
Lighting energy share (%)
Lighting as percentage of total energy. Offices: 20-30%.
Annual maintenance ($)
Total annual building maintenance budget.
Implementation ($/sq ft)
Smart building upgrade cost per sq ft. Retrofit: $3-8, new construction: $1-5.
HVAC savings (%)
Expected HVAC energy reduction. Typical: 15-30% with occupancy + weather optimization.
Lighting savings (%)
Expected lighting energy reduction. Typical: 30-50% with occupancy + daylight harvesting.

What each result means

Annual savings ($)
Total annual savings from energy + maintenance reductions.
Implementation cost ($)
Total one-time cost for smart building upgrade.
Payback period (years)
Simple payback period. -1 = no payback.
5-year ROI (%)
Return on investment over a 5-year period.
Energy reduction (%)
Overall energy cost reduction percentage.
Energy savings ($/yr)
Annual energy cost savings from HVAC + lighting optimization.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Building size (sq ft) = 50000, Energy cost ($/sq ft/yr) = 3.5, HVAC energy share (%) = 40, Lighting energy share (%) = 25 = 8 input(s) provided
  2. Calculate Annual savings
    Annual savings = totalEnergySavings + maintenanceSavings
    40563 = $40,563
  3. Calculate Implementation cost
    Implementation cost = buildingSqFt * implementationCostPerSqFt
    250000 = $250,000
  4. Calculate Payback period
    6.2 = 6.2

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why is the maintenance savings always exactly 15%, regardless of my other inputs?

The engine hard-codes maintenanceSavingsPct at 15 and applies it directly to whatever annual maintenance cost you enter — it isn't derived from HVAC share, lighting share, or building size the way the energy savings are. This reflects a single industry-typical figure for predictive fault detection and automated diagnostics, so if your facility's real maintenance-savings potential is meaningfully higher or lower than 15%, you'll need to adjust the annual maintenance cost input itself to compensate, since the percentage can't be changed directly.

What does a payback period of -1 mean?

The calculator returns -1 instead of a normal year figure whenever totalAnnualSavings comes out to zero or negative — for example, if you set both HVAC and lighting savings percentages to zero. It's a sentinel value meaning the project doesn't produce enough savings to ever pay back the implementation cost as configured, not a literal negative payback year.

Why do I enter HVAC and lighting savings as percentages of my total energy share, rather than directly as dollar savings?

The calculator first splits your total annual energy cost into an HVAC dollar amount and a lighting dollar amount using the energy-share percentages you provide, then applies the expected-savings percentages to each of those dollar amounts separately. Structuring it this way lets the same tool handle buildings with very different HVAC/lighting mixes — a warehouse with a small HVAC share and a hospital with a large one — using the same two-step formula rather than requiring you to pre-calculate dollar savings yourself.

How does the five-year ROI differ from the payback period?

Payback period is simply implementation cost divided by first-year savings, telling you how many years until the upgrade breaks even. Five-year ROI instead projects five years of savings at the same annual rate, subtracts the implementation cost, and expresses the net gain as a percentage of that implementation cost — so it captures the return you get after the payback point, not just when you reach it. Both figures use undiscounted, non-escalating savings, so neither accounts for utility rate inflation or sensor performance drift over time.

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