Your Contractor Sized Your AC by Eyeballing the Square Footage. The AI Used LiDAR.
A five-ton air conditioner sat in the crawlspace of a 1,400-square-foot home in Redding, California, doing almost nothing useful. Manual J load calculation for that house came back at three tons. But the contractor had sized it at 170% of actual need, which according to a Building Science Corporation study for ACEEE, was not unusual, standard practice across an entire subdivision where every house ran between 155% and 185% of calculated load.
I spent twenty-two years watching contractors size HVAC equipment. When I am being charitable, the process involves a tape measure, some mental arithmetic, and a generous safety margin that has nothing to do with safety and everything to do with avoiding a phone call from a homeowner on the hottest day of August.
A Florida Solar Energy Center survey of 489 HVAC contractors, published through ACEEE in the late 1990s, tells the story in numbers that should alarm anyone writing a check for a new system, and no comparably large survey has been published since. Only 33% of respondents used ACCA's Manual J procedure. Another 34.4% used "software," though the survey did not verify whether that software was Manual J-compliant or just a fancier version of guessing. A full 24.2% sized systems using square-footage rules of thumb, which ranged from 350 to 700 square feet per ton. Wide enough to put a two-ton unit or a four-ton unit on the same 2,000-square-foot house depending on which contractor showed up. Another 8.4% used methods the survey categorized as "other estimates."
More than a third admitted to intentionally oversizing on some jobs.
What Oversizing Actually Costs
Conventional assumption says an oversized AC wastes energy because it short-cycles: turn on, cool too fast, shut off, repeat. Wrong mechanism. When the National Renewable Energy Laboratory ran the numbers in 2014, they found that the real penalty comes from parasitic power consumption during off-cycles, the silent draw of controls, crankcase heaters, and standby electronics that keep pulling current whether the compressor is working or not, a background load that grows as a fraction of total consumption with every additional minute the system sits idle waiting for the next thermostat call. Idle costs money. Parasitic loads become a larger and larger share of total consumption as the ratio of off-time to on-time climbs, which means the further you oversize, the worse the math gets.
How much does that cost? HVAC accounts for 40% to 50% of a home's total energy use, according to the University of Maryland's Center for Environmental Energy Engineering. USA Today reported in June 2026 that central air conditioning alone costs American homeowners between $340 and $700 per year depending on climate zone. A 15% to 25% energy penalty from oversizing means $51 to $175 in annual waste that nobody notices because the house is cool and the bill arrives twelve times a year in amounts too small to trigger outrage.
But here is where project managers should sit up. Now compound that waste against equipment cost itself. Angi's 2026 data puts central air installation between $3,900 and $7,900. A right-sized three-ton system for a warm-climate 2,000-square-foot home runs roughly $3,500 installed. An oversized five-ton unit costs closer to $5,200. That is $1,700 in excess equipment cost on day one, before the first kilowatt-hour of wasted electricity.
Over the 15-year expected life of the equipment: $1,700 upfront plus $765 to $2,625 in excess energy. Between $2,465 and $4,325 per home, for a problem that starts with a contractor who did not feel like measuring windows.
Steven Winter Associates found the extreme case. In a multifamily VRF study for NREL, one building was sized at 90% of calculated peak load and another at a staggering 240%, and both sets of residents stayed comfortable through the entire summer. Six to one. That was the cooling electricity ratio per apartment between the right-sized building and the oversized one, a gap so wide that the manufacturer told researchers proper sizing would have saved 24% on equipment costs alone before operating expenses entered the picture. Oversized systems spent most of their operating hours below 33% of maximum capacity, which is the threshold where variable refrigerant flow efficiency collapses.
The LiDAR Fix
Conduit Tech built an iPad-based platform that does something most HVAC contractors have never done: a real load calculation, in the field, while the homeowner watches. A technician walks through the house with a LiDAR-equipped tablet while sensors map every room, every window, and every wall. Within minutes, the software builds a 3D model and runs ACCA-certified Manual J calculations against it. Fifteen minutes from front door to permit-ready sizing report.
ServiceTitan, the trades-software company that went public on Nasdaq as TTAN, announced its acquisition of Conduit Tech in September 2025, with closing expected in Q3 2026. ServiceTitan plans to integrate Conduit's scan-and-calculate workflow into its existing AI automation suite, which already handles scheduling, dispatching, and invoicing for residential contractors. Their pitch is straightforward: a technician who can produce an ACCA-certified load calculation during the sales call closes more deals and installs the right equipment, with fewer callbacks, fewer warranty claims, and higher margins.
This is not the only entry in the space. CoolCalc, Wrightsoft Right-J, and Energy Diagnostics tools all produce Manual J calculations from software. What sets Conduit apart from desktop load-calculation tools is the LiDAR intake itself. Traditional load-calculation software requires someone to measure every room, count every window, assess every insulation type, and key it in manually. That process takes one to three hours for a single-family home. Most contractors skip it because the labor cost eats the margin on the install. Conduit's fifteen-minute scan eliminates the excuse that load calculations take too long to justify.
Why the Industry Resists Right-Sizing
The Florida survey is revealing for what the contractors said about each other. This is a market that has rationalized bad practice for so long that there is no consensus on what good practice looks like, a circular argument where some respondents criticized peers who sized on square footage while others called Manual J itself impractical, and a few complained about contractors who oversize while others protested that undersizing is the real problem because it happens when companies try to win the low bid.
And yet the incentives have not budged. Every incentive in residential HVAC pushes toward bigger equipment. A contractor who installs a right-sized system and gets one callback on a 100-degree day faces a furious homeowner who does not care about load calculations or energy efficiency or parasitic power draw, just that the house is not cool enough. A contractor who installs an oversized system and the homeowner's energy bill is $12 higher per month faces nothing, because nobody has ever been fired for oversizing an air conditioner.
Rewiring America ran the numbers for heat pump sizing using square-footage rules of thumb. Thirty percent of homes would receive a heat pump oversized by more than one ton. But the same methodology also undersized 32% of homes, which means uncomfortable winters or expensive backup resistance heat. Square-footage rules of thumb are not just biased toward big; they are genuinely, demonstrably random.
What to Do With This
If you are a general contractor building spec homes or production housing, the calculus is simple. A LiDAR-based load calculation costs you fifteen minutes of technician time and the price of the software license. Your alternative is a potential $1,700 per home in excess equipment cost that comes straight out of your margin, plus a lifetime of energy waste that lands on your buyer and, eventually, your reputation.
If you are a homeowner replacing your HVAC system, demand a Manual J load calculation before you sign anything. A standalone Manual J from a certified energy auditor costs $150 to $300. If your contractor cannot produce one, or tells you they sized it by "experience," you are about to pay for a machine that is too large, and you will keep paying for it every month for the next fifteen years.
If you are an HVAC contractor reading this and thinking that your customers do not care about right-sizing: you are probably correct, and that is the problem. Most homeowners do not know their system is oversized because they know it is cool inside and the waste stays invisible. Tools like Conduit Tech do not just fix the sizing; they make the calculation visible to the person writing the check. A homeowner who sees a 3D model of their house and a room-by-room load breakdown is a homeowner who understands why three tons is the right answer and five tons is a sales tactic.
Limitations
The Florida contractor survey data is from the late 1990s. No comparably large survey of HVAC contractor sizing practices has been published since, which means we are working with the best available data while acknowledging it may no longer reflect the current state of an industry that has seen tighter energy codes, local jurisdictions requiring load calculations for permits, and a new generation of contractors trained on different tools. It is also plausible that the problem has not moved at all, because the incentive structure has not changed.
NREL's parasitic-power findings are from 2014. Newer variable-speed compressors and inverter-driven systems may reduce the oversizing energy penalty because they can modulate output rather than cycling on and off, which weakens the case for retrofit right-sizing on homes that already have modern equipment installed, though it does nothing to change the upfront equipment cost argument that makes oversizing expensive from day one.
Steven Winter Associates conducted its VRF study in multifamily buildings. Single-family residential systems operate differently, and the six-times electricity difference may not translate directly. Directional conclusion holds; the magnitude is what may shift.
Conduit Tech's integration with ServiceTitan remains incomplete because the acquisition announced in September 2025 is not expected to close until Q3 2026, and until the integration ships, the two platforms operate independently.