Fiberglass Insulation Savings Calculator

Why insulation savings vary

Insulation savings are driven by climate, existing performance, and energy pricing. A cold area with 4,500 heating degree days can deliver 30% more heating-load reduction than a 3,500 degree-day area. Upgrading from R-11 to R-30 reduces conductive heat loss by about 63% because loss scales with 1/R.

Inputs that move results

Area matters linearly. If you insulate 1,200 ft2 instead of 900 ft2, the modeled load change increases by about 33%. System efficiency also matters: a 90% heater uses less input fuel than a 75% unit for the same delivered heat, so the same insulation upgrade can show lower dollar savings with higher efficiency. Cooling savings depend on CDD and COP.

Reading payback, NPV, and IRR

Simple payback is net cost divided by first-year savings, useful for quick screening. NPV discounts future savings; using a 6% discount rate and 3% energy escalation can materially change the investment picture over 10 years. IRR is shown as an approximate rate that makes discounted savings equal the upfront cost. When savings are very small, IRR may return as N/A.

Interpreting energy and carbon outputs

The calculator converts heating load to kWh, therms, or gallons depending on the selected fuel, and includes cooling impacts using COP. If electricity is $0.18/kWh and you save 900 kWh per year, that is $162 annually. Carbon estimates use user-provided factors, letting you match local grid intensity. For mixed systems, treat the CO2 figure as directional and adjust factors to fit.

Practical retrofit planning

Use the example table to sanity-check ranges, then replace with your site-specific values. Consider air sealing as a companion measure, because infiltration losses can be comparable to conductive losses. Document rebates, confirm thickness and installation details, and use the downloads to keep a project record for bids and approvals. If you are comparing contractors, keep inputs consistent and run multiple scenarios for material and labor costs.

FAQs

How accurate are the savings estimates?

They are planning-level estimates using a conduction-focused model. Real savings can be higher or lower based on air leakage, thermostat settings, duct losses, shading, moisture, and installation quality.

What R-values should I enter?

Use your best estimate of current average R-value and your planned target. If insulation varies across areas, choose a weighted average or run multiple scenarios and compare outputs.

Should I include cooling savings?

Include cooling when your home uses air conditioning for a significant season. Enter CDD and a reasonable COP; the calculator will convert the reduced cooling load into electricity savings.

Why does higher efficiency reduce savings?

A more efficient heater needs less fuel to deliver the same heat. Insulation still reduces the heat demand, but the dollar savings can be smaller because each unit of heat already costs less to produce.

What discount rate should I use for NPV?

Use a rate that reflects your opportunity cost and risk, often 3% to 10% for household projects. Higher discount rates place less value on future savings and lower NPV.

Can rebates make payback much faster?

Yes. Rebates reduce net cost immediately, which can shorten simple payback and improve NPV. Enter incentives conservatively and keep documentation for your installer and program requirements.