What Empty Hotel Rooms Cost You in HVAC Waste | ES Global

What Is HVAC Waste in Empty Hotel Rooms Actually Costing Your Property?

Ask a hotel General Manager how much energy their property wastes on empty rooms, and most will say some version of "a lot." Ask them for a number, and the conversation usually stops. Not because the waste isn't real — it's because nobody ever built the number. The monthly utility bill shows one total. It doesn't break out what portion of that total came from an air conditioner running at full comfort in a room nobody has slept in for six hours.

That gap between "a lot" and an actual dollar figure is where energy-saving projects get stuck. A general sense of waste doesn't get budget approved. A specific number does. This article walks through exactly how to build that number for your own property — and what hotels that have already done the math are finding when they act on it.

Why Your Utility Bill Won't Tell You This Number

A property-wide electricity bill answers one question: how much energy did the whole hotel use? It can't answer the more useful question: how much of that was spent conditioning rooms with no one in them? That distinction is exactly what hotel energy monitoring systems are built to solve — breaking a single total into guestroom, HVAC-plant, kitchen, and common-area layers so the waste stops hiding inside one large number.

Without that breakdown, most hotels are left estimating. The good news is that a reasonably accurate estimate doesn't require new hardware — it requires a formula and a few numbers you likely already have.

It also doesn't require a facilities engineer. A General Manager, an owner, or an asset manager preparing a capital-planning conversation can run this calculation from a spreadsheet in under fifteen minutes, using numbers already sitting in the property's utility statements and PMS occupancy reports.

The Simple Formula for Estimating Empty-Room HVAC Waste

At its simplest, the cost of conditioning an empty room comes down to four inputs:

1. Average HVAC draw per room, in kilowatts (kW) — varies by equipment type: PTAC, split system, VRF, or chiller-fed fan coil
2. Your electricity rate, in dollars per kilowatt-hour (US$/kWh)
3. Average vacant hours per room, per day — time between checkout and next check-in, or simply hours a booked room sits empty while the guest is out
4. Number of rooms typically affected across the property

Put together, the formula looks like this:

Estimated daily waste ($) = HVAC draw (kW) × electricity rate (US$/kWh) × vacant hours per room × number of affected rooms

Multiply the daily figure by 365 and you have a rough annual number. It won't be perfectly precise — actual HVAC draw varies by outdoor temperature, equipment condition and room size — but it's accurate enough to turn "a lot" into a figure a General Manager can put in front of ownership.

Research aggregated by the U.S. Department of Energy on occupancy-based hotel controls has found average savings in the range of 10-30% of HVAC energy specifically, once a hotel starts controlling for occupancy instead of conditioning every room continuously — a range worth sanity-checking your own estimate against.

Which HVAC Systems Waste the Most When Rooms Sit Empty

The formula above works for any equipment type, but the size of the number depends heavily on what's actually installed in your guestrooms:

1. PTAC units are the most common source of empty-room waste. They're simple, all-or-nothing systems with no native occupancy awareness, so unless something external controls them, they run at whatever setting the last guest — or housekeeping — left them at.
2. Split systems behave similarly to PTACs in terms of waste potential, though they're often quieter and slightly more efficient per hour of runtime, which can make the waste less obvious on a walkthrough even when the dollar cost is comparable.
3. VRF (variable refrigerant flow) systems are more efficient at the equipment level, but a centralized VRF plant conditioning dozens of rooms simultaneously means a handful of empty, still-conditioned rooms are easy to lose inside a much larger total — exactly the visibility problem a room-level breakdown solves.
4. Chiller-fed fan coils tend to have longer thermal lag, so an empty room can stay conditioned for hours after the system should have backed off, compounding the waste during low-occupancy periods.

This is worth knowing before you run the formula: if your property mixes equipment types, it's more accurate to run the calculation per HVAC type and add the results together, rather than applying one blended draw figure across every room.

A Worked Example

Consider a mid-size 150-room property, largely PTAC units, in a warm climate:

1. Average HVAC draw: 1.2 kW per unit while actively cooling
2. Electricity rate: $0.14/kWh
3. Average vacant-but-conditioned time: 5 hours/day per room (a conservative estimate — many properties see more)
4. Rooms affected: 150

1.2 kW × $0.14 × 5 hours × 150 rooms = $126 per day

$126 × 365 days ≈ $46,000 per year

That's before accounting for peak-season rate increases, larger suites with higher draw, or rooms that sit vacant for longer stretches between bookings. For many properties, the real number is higher. This is precisely the kind of estimate a free, property-specific Hotel Energy Loss Assessment is designed to refine — using your actual room count, HVAC type, occupancy and local electricity rate rather than the placeholder figures used above.

What the Case Studies Show in Practice

Estimates are a useful starting point, but documented, room-level results are more convincing to ownership and finance teams than any formula. A few examples from properties that have already implemented occupancy-based HVAC control:

1. Fiesta Inn recorded up to a 70%+ reduction in monitored room energy consumption — verified at the individual room level rather than estimated across the whole portfolio.
2. Westin Hotel documented 65%+ room-level savings, with zero guest-comfort complaints recorded during the monitoring period.
3. MegaStay showed measurable operational efficiency gains across a multi-property rollout, evidence that the model scales past a single building.

Results like these vary by climate, HVAC type and occupancy pattern — your own property's number will depend on its own baseline. That's exactly why the calculation above, followed by a property-specific assessment, matters more than borrowing someone else's headline percentage.

Why Generic Fixes Rarely Close This Gap

Hotels have tried several approaches to this problem over the years, with mixed results:

1. Keycard energy switches only detect whether a card is in the slot — not whether the room is actually occupied, and they break down entirely once a property moves to mobile or keyless entry.
2. Fixed HVAC schedules treat every room the same regardless of actual guest behavior, so they either waste energy on early-empty rooms or risk discomfort by cutting conditioning too aggressively.
3. Full thermostat replacement programs can address the problem, but they add equipment cost, installation labor and room downtime across every guestroom in the property — a heavier lift than many renovation budgets can absorb in one cycle.

The mechanics of a better approach — how occupancy sensors, HVAC control and temperature recovery actually work together in a guestroom — are covered in detail in our guide to occupancy-based HVAC control. Worth reading in full if you want the operational side of this problem; this article stays focused on the financial side.

Turning the Number Into a Decision

Once you have a credible waste estimate, the next question is simple: is it worth fixing? That decision usually comes down to a short checklist:

1. Does the estimated annual waste justify the cost of a room-level control system, once you weigh installation, maintenance and payback period?
2. Can the solution work with your existing HVAC — PTAC, split system, VRF or chiller — without a full equipment swap?
3. Will guests notice any difference in comfort, or does the system recover the room to full comfort before they return?
4. Can you verify the savings after installation against the baseline you calculated here, rather than taking a vendor's advertised percentage on faith?

ES Global's own positioning is built around exactly that last point: a minimum 20% reduction in per-room energy consumption is offered as a guarantee, with the investment returned if that threshold isn't met — a structure that only makes sense once you have a real baseline number to measure against.

It's also worth treating the delay itself as a cost. The math in this article doesn't reset each month — it compounds. A property sitting on a $46,000-a-year estimate that waits twelve months to act hasn't saved that money; it's simply spent it on nothing. The waste doesn't pause while a decision gets made.

Get Your Property's Exact Number

The formula above will get you a reasonable estimate in about ten minutes. For a precise, property-specific breakdown — using your actual room count, HVAC type, occupancy percentage, country and local electricity rate — the Free Hotel Energy Loss Assessment takes a similar amount of time and returns an estimated annual waste figure, a realistic recovery potential, and a benchmark against similar properties, with no cost or commitment attached.

If you'd rather understand how the underlying system works before requesting a number, start with how occupancy-based HVAC control works, or see the full breakdown of features and hardware. Either way, the goal is the same: replace "a lot" with a number your ownership group can actually evaluate.

The Bottom Line

"A lot" isn't a number ownership can act on. A formula, a worked example, and a documented case study are. Whether your property loses tens of thousands of dollars a year to empty-room HVAC waste or considerably more, the first step is the same: build the number, then decide whether it's worth fixing. Start your free assessment to get your property's exact figure.