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?
The cost math: base install runs $1.50–$3.00 per square foot. Targeting R-60 (the retrofit recommendation) adds about 15% over the R-49 minimum. Removal of existing material adds $1.50–$3.50 per square foot. Air sealing adds $300–$1,200 fixed.
The rebate math is deliberately shown as TWO separate figures, never one. Xcel's rebate is 30% of your computed project cost, capped at $500 for attic insulation — this calculator applies the cap but does not attempt to compute the exact dollar effect of Xcel's 1.5x gas-heat multiplier, since its precise mechanics (whether it multiplies the percentage or the cap) aren't specified precisely enough in this site's verified program facts. Efficiency Works' rebate is $0.77 per square foot for flat-ceiling attic insulation, capped at 100% of project cost, and applies ONLY to Longmont Power & Communications electric customers — roughly 61% of the city. Nothing published by either program states they combine, so this calculator never adds them.
According to Xcel Energy, “Xcel's insulation and air sealing rebates pay 30% of project cost for gas-heat customers, up to $500 for attic insulation, $350 for wall insulation, and $400 for air sealing, with a 1.5x multiplier for customers whose heating fuel is Xcel gas.”
According to Efficiency Works (Platte River Power Authority program, for Longmont Power & Communications electric customers), “Efficiency Works pays $1.16 per square foot for most insulation measures (conditioned crawl space, basement wall, cantilever floor, exterior wall, cathedral ceiling, conditioned attic) and $0.77 per square foot for flat-ceiling attic insulation, available only to residential electric customers of Longmont Power & Communications.”
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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 — the model energy code for Climate Zone 5 calls for R-49 to R-60 attic insulation; ask what your contractor is quoting to. (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 nothing published by Xcel or Efficiency Works states that a single project can claim both, and they're structured completely differently (a percentage-of-cost cap vs. a flat per-square-foot rate). Adding them together would be a claim this site can't back up. You get two honest, separate figures instead.
Why doesn't the calculator compute the exact dollar amount for Xcel's 1.5x gas-heat multiplier?
Because Xcel's published rebate summary states the 1.5x multiplier as a rule but doesn't specify precisely enough for this calculator to compute an exact adjusted dollar figure without guessing at the mechanics. The base 30%-of-cost-capped-at-$500 figure is computed directly; ask your contractor to confirm the exact gas-heat-adjusted number for your project.
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 figure shown here does not apply to your address; Xcel's rebate applies regardless of which electric utility you have.
Does this estimate include 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.
How accurate is this estimate?
It's a planning-stage range built from typical Longmont-area pricing patterns, not a quote. The free in-home estimate gives exact numbers based on what a contractor actually sees in your attic.
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