Window Replacement vs Storm Windows Calculator — Rex's Toolbox

Rex says

Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.

Try a scenario

Click to load — tweak from there.

Inputs

Number of windows

Full replacement cost per window($)

Storm window cost per window($)

Annual energy savings, full replacement($)

Annual energy savings, storm windows($)

Comparison horizon(yrs)

Result

Better net savings option

Storm Windows

Full replacement payback

22.3

Storm windows payback

10.0

Net savings difference over horizon

$3,450

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How to use this

1Enter number of windows.
2Enter full replacement cost per window ($).
3Enter storm window cost per window ($).
4Enter annual energy savings, full replacement ($).
5Enter annual energy savings, storm windows ($).
6Enter comparison horizon (yrs).
7Read your better net savings option on the right — it updates as you type.
8Hit Share to keep the scenario or send it to someone.

About this calculator

Full window replacement is expensive but delivers the biggest efficiency and comfort gain plus resale value. Adding storm windows over your existing windows costs a fraction as much and can capture a meaningful chunk of the energy savings. This calculator compares upfront cost against annual energy savings for each option to find which one pays back faster and saves more over your horizon.

FormulaPayback = Upfront Cost ÷ Annual Energy Savings. Net Savings = (Annual Savings × Horizon) − Upfront Cost.

Worked example

Using the values the calculator loads with:

Inputs

Number of windows: 12
Full replacement cost per window: 650 $
Storm window cost per window: 150 $
Annual energy savings, full replacement: 350 $
Annual energy savings, storm windows: 180 $
Comparison horizon: 15 yrs

Results

Better net savings option: Storm Windows
Full replacement payback: 22.3
Storm windows payback: 10
Net savings difference over horizon: $3,450

What each field means

Inputs

Number of windows: The number of windows used in the calculation. Starts at 12 so you have a working example on load.
Full replacement cost per window ($): The full replacement cost per window used in the calculation, measured in $. Starts at 650 $ so you have a working example on load.
Storm window cost per window ($): The storm window cost per window used in the calculation, measured in $. Starts at 150 $ so you have a working example on load.
Annual energy savings, full replacement ($): The annual energy savings, full replacement used in the calculation, measured in $. Starts at 350 $ so you have a working example on load.
Annual energy savings, storm windows ($): The annual energy savings, storm windows used in the calculation, measured in $. Starts at 180 $ so you have a working example on load.
Comparison horizon (yrs): The comparison horizon used in the calculation, measured in yrs. Starts at 15 yrs so you have a working example on load. Accepted range: 1–40 yrs.

Results

Better net savings option: Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Full replacement payback: Returned as a length of time. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Storm windows payback: Returned as a length of time. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Net savings difference over horizon: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Do storm windows really save meaningful energy?

Good storm windows can cut air leakage significantly and capture roughly half the efficiency gain of full replacement at a fraction of the cost, which is why they often win on payback speed.

Does full replacement add more resale value?

Yes — new energy-efficient windows are consistently one of the higher ROI home improvements at resale, an advantage storm windows don't provide since old windows remain underneath.

Can I do storm windows now and replace later?

Yes, many homeowners use storm windows as a bridge to stop the bleeding on energy costs, then budget for full replacement in a later renovation cycle.

Accuracy and limitations

Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.

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Cite this calculator

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APA

RevenueLab. (2026). Window Replacement vs Storm Windows Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/window-replacement-vs-storm-windows

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/window-replacement-vs-storm-windows" target="_blank" rel="noopener">Window Replacement vs Storm Windows Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Window Replacement vs Storm Windows Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/window-replacement-vs-storm-windows) (2026).