Your project
Most Longmont homes run 1,200-2,500 sq ft. Conditioned-area square footage is fine if you don't know exact attic footprint.
How it works
How does this calculator work?
This calculator does not compute a dollar cost range. This site has no single sourced per-square-foot install rate for the Longmont market — actual price depends on the contractor, the material, and site conditions in ways a generic figure can't honestly capture. What reliably raises cost: targeting R-60, the high end of ENERGY STAR's Climate Zone 5 range, over R-49 at the low end; removing existing material before install (pre-1990 builds, contamination, settled cellulose); and pairing air sealing with insulation. The free in-home estimate turns those specifics into an actual number.
Rebates are not part of that either. This calculator does not compute a rebate amount. Xcel Energy publishes its own attic insulation rebate terms, open to Longmont addresses regardless of electric utility; Efficiency Works publishes its own, open only to Longmont Power & Communications electric customers — the Colorado Geospatial Portal's own utility-territory data puts that at roughly 61% of the city. Ask your contractor to confirm which program applies to your address and what it pays.
For current Xcel rebate amounts and program rules, see the Xcel Energy insulation and air-sealing rebates page. For Efficiency Works eligibility and current incentive values, see Efficiency Works home rebates. Eligibility may depend on which electric utility serves your address, program funding levels, and qualifying product specifications.
According to Efficiency Works (Platte River Power Authority program, for Longmont Power & Communications electric customers), Efficiency Works pays a per-square-foot incentive for most insulation measures (conditioned crawl space, basement wall, cantilever floor, exterior wall, cathedral ceiling, conditioned attic) and a separate per-square-foot rate for flat-ceiling attic insulation, available only to residential electric customers of Longmont Power & Communications, with the current rates published on its own incentive sheet.
According to Xcel Energy, its Insulation and Air Sealing product write-up requires a pre-improvement blower door test in CFM 50 — cubic feet per minute at 50 pascals — on any project that has not already had a recent home energy audit that included one; unless that test finds the home already tight enough by Xcel Energy's own measure, air sealing is required and a post-improvement test must show at least a 20% reduction in air leakage before attic or wall insulation can qualify for a rebate, and the insulation measures carry R-value conditions of their own beyond the blower-door result.
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Tell Us About Your Home
30 seconds to fill out. Free quote, no high-pressure follow-up.
We've Got It. Here's What Happens Next.
We've got your info and are routing it to a local pro. When they call, here's what to look for in the quote you receive: (1) R-value target — ask what R-value your contractor is quoting to, in writing, and confirm the figure your permit is reviewed against with the City of Longmont's building department. (2) Air sealing scope — insulation alone does nothing if air leaks aren't sealed first, and Xcel requires a blower door test to rebate it. (3) Rebate handling — ask which programs your specific address qualifies for. Xcel and Efficiency Works are separate programs with separate paperwork, and not every address qualifies for both. (The federal IRA Section 25C tax credit ended December 31, 2025 — no federal insulation credit applies to 2026 work. Xcel Energy's insulation and air-sealing rebate remains active for its gas and electric customers. Longmont Power & Communications electric customers may separately qualify for an Efficiency Works rebate — check your bill to see which utility serves your address. Boulder County EnergySmart pays a third, income-qualified-only rebate as of January 1, 2026.) (4) Removal scope — older homes often need old insulation removed before new install. If a quote skips all four, get another quote.
Frequently asked
Frequently asked about insulation cost calculator
Why doesn't this calculator show one combined rebate-adjusted price?
Because the only published combined figure is an illustration this site doesn't adopt. Efficiency Works' incentive sheet lists an Xcel figure beside its own and totals the two for one example attic project — so Efficiency Works does publish an illustrative combined total — but Xcel's own rebate sheet is silent on the combination, the Xcel figure in that table doesn't match any Xcel per-measure cap this site has independently verified, and the two programs are structured completely differently (a percentage-of-cost cap vs. a flat per-square-foot rate). Adopting Efficiency Works' total would be a claim this site can't back up. This calculator doesn't show a rebate-adjusted price at all — it scopes your project and leaves each program's figure to the program.
I'm not sure if I have LPC electric — what should I do?
Check your electric bill — the utility name is printed on it. If it's not Longmont Power & Communications, the Efficiency Works rebate does not apply to your address at all; Xcel's rebate applies regardless of which electric utility you have.
Does this tool cover asbestos or vermiculite testing?
No — if your attic has silvery-gray, pebble-shaped insulation (possible vermiculite), that's a separate testing and, if needed, professional-removal scope. See the vermiculite and asbestos insulation removal page — Xcel also bars blower door testing (needed for its rebate) on affected homes until that material is professionally removed.
Why doesn't this calculator show a dollar cost estimate?
Because no single per-square-foot install rate is sourced for the Longmont market — pricing depends on the contractor, the material, and site conditions enough that stating one number here would be a guess, not a fact. This tool scopes your project instead; the free in-home estimate turns that scope into an actual price based on what a contractor sees in your attic.
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