A calculator for the annual Local Law 97 penalty from a year of utility bills, the 2024 and 2030 limits by property type, and an honest account of what window replacement does for a building’s number — and what it cannot do on its own.
Short version. Local Law 97 puts a carbon limit on every New York building over 25,000 square feet and fines the owner $268 for every ton over it, each year. The limits roughly halve in 2030. Windows are a real part of the answer — on a pre-war co-op with single-glazed sash they can be a large part — but they are rarely the whole answer, and a board that buys windows before it understands its number is spending in the wrong order. Use the calculator, then read what windows can and cannot do for the result.
Enter the building’s gross floor area, its property type and a year of utility use (from the bills or the Portfolio Manager benchmarking report). The calculator applies the law’s coefficients and limits for 2024–2029 and 2030–2034 and shows the annual penalty at $268 per ton over the limit.
Coefficients: electricity 0.000288962 tCO₂e/kWh (2024–29) and 0.000143068 (2030–34); natural gas 0.00005311 tCO₂e/kBtu (100 kBtu per therm); No. 2 oil 0.00007421 tCO₂e/kBtu at 138.5 kBtu/gal; district steam 0.00004493 tCO₂e/kBtu at 1,194 kBtu/Mlb. Limits per the law and the Department of Buildings’ property-type tables; the DOB list has sixty types — check yours. Estimate only; the filed report must be prepared by a registered design professional.
Local Law 97 of 2019, part of the Climate Mobilization Act, covers buildings over 25,000 gross square feet, plus groups of buildings on one lot or under one condominium board that add up to 50,000. Each covered building gets an annual emissions limit: its floor area multiplied by an intensity figure for its property type. Every May the owner files a report, stamped by an engineer or architect, of the previous year’s emissions, calculated from the utility bills with fixed carbon coefficients. If the emissions exceed the limit, the penalty is $268 per ton of CO₂-equivalent over, every year it happens. The first compliance period runs 2024 through 2029; the second, 2030 through 2034, cuts most limits by about half; the law tightens again in 2035 and 2040 on the way to an 80% reduction by 2050.
Two details matter for planning. The electricity coefficient drops by about half in 2030 because the state grid is expected to be cleaner, so a building that has already moved heating from gas to electric heat pumps gets a second benefit then. The gas coefficient never changes, because a therm burned in the basement makes the same CO₂ whatever the year. That is why the law pushes fuel-burning buildings hardest, and why most pre-war residential buildings — gas or oil boilers, steam radiators, single-glazed windows — are the ones with a 2030 problem.
The limit is on carbon, and in a heated building carbon comes mostly from the boiler. Windows do not burn fuel; they decide how hard the boiler works. On a pre-war building with original single-glazed or 1980s aluminium windows, the glazing can account for a quarter to a third of the heat loss, and replacing it with thermally broken frames and low-E insulated units typically cuts heating fuel by 10–20%, sometimes more where the old windows also leaked air. On a building that already has decent double glazing, new windows do less, and the money belongs in the boiler, the controls and the roof first.
What windows uniquely do is make the other measures work. A heat pump conversion is sized to the heat loss, and a building that keeps single glazing needs a bigger, costlier system and more electricity to run it; new windows shrink the load first. That is the honest case for windows under Local Law 97: not that they clear the limit alone, but that they are the envelope step that makes the electrification step affordable. Our building energy performance page and the LL97 explainer cover the wider strategy; the insulated glass page covers what the glass itself does.
| Step | Why first | Where windows fit |
|---|---|---|
| 1. Benchmark and read the number | You cannot plan against a figure you do not have; the Portfolio Manager report and the May filing give it | Use the calculator above with last year’s bills as a first look |
| 2. Energy audit | Finds where the heat goes: distribution losses, controls, envelope, windows | The audit quantifies what the windows are costing; ask for the window line specifically |
| 3. Controls, steam balancing, insulation | Cheapest tons: a boiler that cycles less and pipes that are insulated | None yet |
| 4. Windows | The envelope step: cuts the load, stops the drafts, and is visible to shareholders | Whole-building programme or the worst elevations first; co-op standard set once for every apartment |
| 5. Heating conversion | Heat pumps sized to the reduced load; gets the 2030 electricity benefit | Windows should be in before this is sized |
For a residential board the practical questions are: does the building exceed the 2030 limit (most pre-war buildings do), what is the penalty exposure per year from 2030, and what does a window programme cost against it. A 60,000-square-foot gas-heated pre-war co-op is often 80–250 tons over its 2030 limit, which is $21,000–$67,000 a year in penalties, indefinitely. A whole-building window replacement on that building is a capital cost the board can amortise; the penalty is not. We prepare the window part of that case for boards: a survey of the existing units, the specification, a phased installation plan by elevation or by line, and the numbers the engineer needs for the audit. See window replacement in NYC and our Brooklyn co-op page for how the programme runs.
It uses the coefficients and the main property-type limits from the law and the Department of Buildings rules, with one year of utility figures you type in. The filed report uses sixty property types, exact meter data, and adjustments for things like district steam, on-site renewables and mixed-use floor areas; only an engineer’s report counts. Treat the result as a first look that tells a board whether it has a 2024 problem, a 2030 problem or neither, and how big the window question is. Penalty mitigation, good-faith adjustments and the 2024–29 rules for buildings that were close to compliance are decisions for the building’s engineer and attorney.
New York City’s building emissions law: buildings over 25,000 square feet get an annual carbon limit based on floor area and property type, report emissions every May, and pay $268 per ton over the limit. Limits roughly halve in 2030.
Annual emissions (utility use multiplied by fixed carbon coefficients) minus the building’s limit (floor area times the intensity figure for its property type), multiplied by $268 per ton of CO2-equivalent over. The calculator on this page does that sum.
Yes, in proportion to how bad the old ones are: replacing single-glazed or 1980s aluminium windows typically cuts heating fuel 10–20%, and reduces the load a heat-pump conversion has to be sized for. On a building with decent double glazing they do less, and the boiler and controls come first.
Rarely. Most pre-war gas-heated buildings need to cut fuel by 40% or more for 2030, which takes windows plus heating conversion. Windows are the envelope step that makes the conversion smaller and cheaper.
From 0.00675 to 0.00334664 tCO2e per square foot — about half. A 60,000-square-foot co-op’s limit goes from 405 tons to about 201 tons a year.
If the building is over 25,000 gross square feet, yes; smaller buildings are exempt, and some rent-regulated and affordable buildings follow a prescriptive-measures track instead of the limit. Check the DOB covered-buildings list.
Yes: a survey of the existing windows, a specification, phasing by elevation or line, and the figures the energy auditor needs for the window line. We install the programme afterwards.
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About this page. Written by Alex GC Inc. d/b/a Alex Glass Construction and reviewed before publication by Aleksandr Chernovolenko, Managing Partner, with our design and estimating lead and a field foreman. Our foremen hold the NYC DOB Site Safety Training supervisor card and our crews the 40-hour worker card; we are certified to fabricate, install and service Alutech and Everest aluminum systems. Facts are drawn from our own projects, manufacturer test data and the applicable codes; where we are giving an opinion, we say so. Last reviewed September 2026. Credentials
Send the building address, the floor area and last year’s utility totals. We will give the board the window part of the plan — survey, specification, phasing and the figures the auditor needs.
