Climate ToolsetHome Energy Audit Calculator
Estimate your annual energy costs and see how much you could save with upgrades.
Annual Energy Summary
Annual Energy Cost
$2,760
Cost Per Sq Ft
$1.38
Estimated Savings by Upgrade
Insulation Upgrade
15% reduction
$414/yr
Energy-Efficient Windows
10% reduction
$276/yr
HVAC System Upgrade
20% reduction
$552/yr
LED Lighting
5% reduction
$138/yr
Total Potential Savings (all upgrades)
$1,380/yr
Savings stack on the same starting bill, so the "all upgrades" total is an optimistic ceiling, not a promise. Real bundled retrofits usually land below the sum of their parts — see the accuracy notes below.
When You'd Actually Use This
Dana owns a 1978 ranch house in Ohio: 1,850 sq ft, $165/month electric, $95/month gas. That's $3,120 a year, or $1.69 per square foot. Her neighbor's comparable house runs about $1.05/sq ft. A contractor quotes $9,400 for attic and rim-joist insulation. Before she signs anything, she wants a number: at a 15% reduction, insulation would return roughly $468/year, which is a 20-year simple payback — too slow on its own, but far better if she bundles it with the HVAC replacement she already needs.
That is the job this calculator does. It converts your bills into an annual figure, normalizes it per square foot so you can compare against benchmarks, and puts a rough dollar value on each upgrade so you can rank them before spending money on a professional audit or a contractor bid. It is a triage tool, not a substitute for a blower-door test.
Typical users: homeowners deciding which retrofit to do first, buyers estimating carrying costs on a listing, renters checking whether a bill is abnormal, and landlords comparing units in the same building.
Understanding Energy Use Intensity and Savings Percentages
Every number here comes from three steps. First, annual cost: (electricity + gas) × 12. Second, cost intensity: annual cost ÷ square footage. Third, each upgrade's savings: annual cost × reduction %.
The notation you'll see elsewhere
Professional auditors report EUI (Energy Use Intensity) in kBtu/sq ft/yr— energy, not dollars. Utilities bill electricity in kWh (kilowatt-hours) and gas in therms or CCF(hundred cubic feet). The conversions worth memorizing: 1 kWh = 3.412 kBtu, 1 therm = 100 kBtu, and 1 CCF of natural gas ≈ 1.03 therms. This tool deliberately works in dollars per square footinstead, because that is the unit that actually changes your decision — and because a dollar figure needs no rate lookup.
The trade-off: dollars per square foot moves when your utility raises rates, even if your house did not change. Energy intensity (kBtu/sq ft) is rate-independent. If you want to track whether your house improved rather than whether your rates did, record kWh and therms from the bill alongside the dollars.
The five mistakes people make
- Using one month's bill as the average.A January gas bill in Minnesota can be 6× the July bill. Multiplying a peak month by 12 can overstate annual cost by 40% or more. Use a 12-month average.
- Counting unconditioned square footage. An unfinished basement or detached garage inflates the denominator and makes an inefficient house look efficient. Count conditioned (heated/cooled) floor area only.
- Adding every upgrade percentage together.Savings interact. Once new insulation cuts the heat load, the high-efficiency furnace has less load to save on. Bundled retrofits routinely deliver 60–80% of the arithmetic sum, not 100%.
- Applying a whole-bill percentage to the wrong end use.Insulation and windows affect heating and cooling, not the refrigerator or the dryer. If HVAC is only 40% of your load, a "15% insulation savings" on the total bill is optimistic for a mild climate.
- Ignoring fixed charges.Most bills carry a $10–$25/month service or delivery charge that no retrofit removes. On a $95 bill, that is 10–25% of the total that is simply not addressable.
Benchmarks, Upgrade Costs, and Realistic Paybacks
Compare your cost per sq ftagainst these ranges. They are rough US single-family figures, meant for ranking decisions — not for a rebate application.
Annual energy cost per square foot
| $/sq ft/yr | Reading | What it usually means |
|---|---|---|
| Under $0.75 | Efficient | Tight envelope, modern HVAC, or a mild climate. Chase appliances and behavior, not the shell. |
| $0.75 – $1.25 | Typical | Most post-1990 US homes. Targeted air sealing and a smart thermostat are the cheap wins. |
| $1.25 – $2.00 | High | Common in older homes or cold/hot climates. Envelope work usually pays. Get a blower-door test. |
| Over $2.00 | Investigate | Suspect a failing system, electric resistance heat, a leaky duct run, or a wrong square-footage entry. |
Upgrade costs and where the percentages come from
| Upgrade | Modeled cut | Typical installed cost | Realistic range | Simple payback |
|---|---|---|---|---|
| Insulation + air sealing | 15% | $2,500 – $10,000 | 5% – 20% | 7 – 20 yrs |
| Energy-efficient windows | 10% | $8,000 – $25,000 | 4% – 12% | 20 – 40+ yrs |
| HVAC upgrade / heat pump | 20% | $6,000 – $20,000 | 10% – 30% | 8 – 25 yrs |
| LED lighting | 5% | $100 – $600 | 2% – 8% | Under 2 yrs |
The pattern worth noticing:LED lighting has the smallest savings and by far the best payback. Windows have the second-largest headline savings and the worst payback of the four. Ranking upgrades by the dollar figures above alone will point you at the wrong project — always divide savings into cost.
Pre-Flight Checklist: Getting the Inputs Right
Work through these before you trust the output, and again before you show a contractor any number from this page.
- Pull 12 consecutive months of bills and average them. Do not multiply a single winter or summer bill by 12.
- Enter conditioned square footage only — exclude unfinished basements, attics, garages, and porches.
- If your heat is electric (resistance or heat pump), enter $0 gas rather than guessing; a phantom gas bill inflates every savings line.
- Check whether propane, heating oil, or wood is part of your heat. This tool has no field for them, so the annual cost will read low.
- Subtract nothing for fixed delivery charges in the input, but remember they are not addressable when you judge payback.
- Get a contractor quote before you compare payback — the savings side of the ratio is the easy half.
- Rank by payback (cost ÷ annual savings), not by the size of the savings number.
- Check your utility, state, and federal rebate programs before signing; incentives can cut effective cost by 30% or more and completely reorder the ranking.
- For anything over roughly $5,000, get a professional audit with a blower-door test and, ideally, thermal imaging. A $300–$600 audit protects a five-figure decision.
Accuracy: What Is Exact and What Is an Estimate
Exact arithmetic. The annual cost, the cost per square foot, and each savings line are exact evaluations of the formulas above, to the cent, on the numbers you typed. If you enter $150 and $80 on 2,000 sq ft, $2,760/yr and $1.38/sq ft are not approximations. Every value is computed in your browser; nothing is rounded for you beyond the display.
Estimated, and only that. The four reduction percentages are planning-grade rules of thumb drawn from typical retrofit outcomes. Your actual result depends on climate zone, existing insulation R-value, air-leakage rate, duct condition, equipment age and efficiency, occupancy, and thermostat behavior. Two identical houses on the same street can differ by 30% on the same retrofit.
Not modeled at all.Rate escalation, seasonal rate tiers, time-of-use pricing, fixed service charges, propane and heating oil, solar generation or net metering, financing interest, maintenance costs, resale value, and the interaction between bundled upgrades. Rebates, tax credits, and utility incentives are also not modeled — eligibility rules change and vary by jurisdiction, so verify current terms with the program administrator or a tax professional before counting on them.
Professional judgment.These outputs are not a home energy assessment, an engineering report, tax advice, or a code-compliance determination. Combustion safety in particular — air sealing a house with an atmospherically vented furnace or water heater can create a backdrafting hazard — is a job for a certified auditor with a combustion analyzer, never a web calculator. Use this to decide what to investigate; use a professional to decide what to build.
Privacy: Your Bills Stay on Your Device
This calculator runs entirely as local processing in your browser. Your square footage and your electricity and gas amounts are held in component state, used for the arithmetic, and discarded when you close the tab. There is no server call, no account, no upload, and no storage of your figures. We do not verify, look up, or link your utility account, address, or usage history.
Utility bills are quietly sensitive: they reveal occupancy patterns, whether a home is vacant, and household size. Keep that in mind if you paste real figures into anyonline tool. It is safe to work with rounded numbers here — a bill entered as $150 instead of $147.83 changes nothing about which upgrade wins.
FAQ
Which bill numbers should I enter — last month's or an average?
Use a 12-month average. Add up a full year of electricity charges and divide by 12, then do the same for gas. Most utilities show a 12-month usage graph or a "monthly average" line on the bill itself. Entering a single January gas bill and letting the tool multiply by 12 is the single most common way to get a wildly wrong annual cost.
Can I really add all four upgrades together and save that much?
No. The "total potential savings" line applies every percentage to the same original bill, so it is an upper bound. In practice the upgrades overlap: insulation reduces the heating load that a new furnace would have saved on. Plan on roughly 60–80% of the arithmetic total when you bundle all four, and confirm with a modeled audit if the project is large.
My cost per square foot is $2.40. Is my house broken?
Maybe, but check the inputs first. The three usual explanations are electric resistance heat (baseboards or a furnace with strip heat), a square-footage entry that excluded a finished basement, or a genuine problem such as a failing heat pump or disconnected ductwork. If the inputs are right and you are above $2.00, that is exactly the case where a $300–$600 professional audit pays for itself.
Why does this show windows saving so much when everyone says windows never pay back?
Both are true. Windows can plausibly cut 10% of a bill, but at $8,000–$25,000 installed, that 10% typically needs 20 to 40 years to recover. The savings figure and the payback figure answer different questions. Always divide the contractor quote by the annual savings before ranking a project — the reference table above shows how badly the ranking flips when you do.
I heat with propane or heating oil. Where do I put that?
There is no dedicated field, so convert it: take your annual propane or oil spend, divide by 12, and enter that as the monthly gas figure alongside any actual gas service you have. The savings percentages still apply reasonably, since the upgrades reduce heating load regardless of the fuel burned.
Do rebates and tax credits change the answer?
Frequently, and sometimes completely. Utility rebates, state programs, and federal credits can cut effective project cost by 30% or more, which can turn a 20-year payback into a 12-year one and move a project up your list. This tool does not model any of them because eligibility and amounts change by year and jurisdiction. Confirm current terms with the program administrator or a tax professional.
When should I stop using this and hire a professional auditor?
When you are about to spend more than about $5,000, when your cost per square foot is above $2.00 and you cannot explain why, or any time air sealing is on the table in a house with an atmospherically vented furnace or water heater. A certified auditor runs a blower-door test, checks combustion safety, and models your specific house — things no percentage-based estimate can do.
Is my utility data sent anywhere?
No. Every calculation runs locally in your browser, and nothing you type is transmitted, stored, or associated with an account. Closing the tab discards it.