If you’ve been researching Xcel Energy’s insulation rebate program in Colorado, you’ve probably come across the phrase “blower door test” or seen the acronym CFM50 buried in the program requirements. These aren’t bureaucratic obstacles — they’re the technical backbone that determines whether your air sealing work qualifies for a rebate at all. Understanding what these tests measure and why they matter can mean the difference between a rebate check in the mail and a rejected application.
At Insulation Nation, we work with Denver Metro homeowners and Colorado Front Range customers every week who want to take advantage of Xcel Energy’s air sealing and insulation rebates. We find that the homeowners who understand the blower door process upfront tend to have smoother rebate experiences. This guide breaks down the science in plain language and explains exactly how the CFM50 threshold connects to your rebate eligibility.
What Is a Blower Door Test?
A blower door test is a diagnostic procedure used to measure how airtight your home is. A certified technician temporarily mounts a powerful, calibrated fan into the frame of an exterior doorway. The fan depressurizes the house — pulling air out and lowering the indoor air pressure — so that outside air rushes in through every unsealed gap, crack, and penetration in your building envelope.
While the fan is running, your technician can walk through the home with an infrared camera or a smoke pencil to locate exactly where air is sneaking in: around recessed lights, through attic bypasses, along rim joists, and at plumbing and electrical penetrations. According to the U.S. Department of Energy, calibrated blower doors measure airflow in cubic feet per minute at a standardized 50-pascal pressure difference — which is why the reading is expressed as CFM50.
The test is conducted both before and after air sealing work is performed. The pre-test establishes your baseline; the post-test verifies how much leakage was actually reduced. That improvement ratio is what Xcel Energy uses to determine your rebate eligibility.
What Does CFM50 Actually Measure?
CFM50 stands for cubic feet per minute at 50 pascals. It represents the volume of air flowing through the blower door fan when your home is depressurized to 50 pascals — roughly equivalent to a 20-mph wind pressing on all sides of your house simultaneously. The higher the CFM50 number, the more air your home is losing through gaps and cracks.
To put this in perspective: a very leaky older Colorado home might test at 3,500 CFM50 or higher, while a well-sealed modern home might come in under 800 CFM50. CFM50 alone doesn’t define “good” or “bad” — the number must be interpreted in context of the home’s volume and surface area — but as a before-and-after comparison metric for rebate purposes, it’s precise and consistent.
A related metric you may encounter is ACH50 (air changes per hour at 50 pascals), which factors in your home’s volume. Xcel Energy’s program uses the NACH (natural air changes per hour) threshold of 0.50 as a baseline: if your home is already at or below 0.50 NACH, it is considered sufficiently airtight and air sealing is not required before insulation work can qualify for a rebate.
Xcel Energy’s CFM50 Reduction Requirement for the Air Sealing Rebate
According to the Xcel Energy 2024 Rebate Summary, the qualifying minimum standard for the air sealing rebate is a 20% reduction in CFM50 from the pre-improvement blower door test to the post-improvement test. If your home started at 2,000 CFM50, your post-work test needs to show a reading no higher than 1,600 CFM50 for the work to qualify.
As of the 2024 rebate summary, the maximum air sealing rebate for customers who heat with Xcel Energy natural gas or electricity is up to $200, capped at 30% of the project cost. For customers with Xcel electric service only (but a non-Xcel heating fuel), the maximum is $15. These figures are subject to change, and program rules may be updated — always verify current eligibility requirements directly with Xcel Energy before scheduling work.
| Customer Type | Minimum Standard | Maximum Rebate |
|---|---|---|
| Xcel natural gas or electric heat customers | 20% reduction in CFM50 | Up to $200 (30% of cost) |
| Xcel electric service only (non-Xcel heating fuel) | 20% reduction in CFM50 | Up to $15 (30% of cost) |
Air Sealing Rebate Readiness Checklist
Before a Colorado homeowner starts air sealing work, the safest move is to confirm that the project can be documented the way Xcel Energy expects. The checklist below is not a substitute for current program rules, but it gives you a practical way to spot problems before the install begins.
| Checkpoint | Why it matters for the rebate | What to verify before work starts |
|---|---|---|
| Participating contractor | Xcel states that insulation and air sealing upgrades must be completed by a participating contractor. | Confirm the contractor is currently eligible for the Colorado program before signing. |
| Pre-work blower door result | The air leakage baseline is needed to show the reduction after air sealing. | Make sure the test is performed and recorded before sealing work begins. |
| Scope tied to leakage reduction | General caulking is not the same as a measured air sealing project. | Ask which bypasses, attic penetrations, rim areas, or envelope leaks are included. |
| Post-work blower door result | The project needs measurable improvement, not just a visual inspection. | Confirm a post-improvement test will be completed and documented. |
| Invoice detail | Rebate review can fail when the paperwork does not separate eligible work clearly. | Require line items for air sealing, insulation, test dates, address, and payment status. |
The air sealing rebate can also stack with the insulation rebates and the Whole Home Efficiency 25% bonus rebate if you complete three or more qualifying measures within a two-year period. A separate $600 bonus rebate is available when air sealing and insulation are completed within six months of a qualifying space-heating heat pump installation.
Why Blower Door Testing Is Required — Not Optional
Xcel Energy’s program rules require pre- and post-improvement blower door tests for all projects. This is not administrative box-checking. The tests serve three important functions:
- Baseline documentation: The pre-test confirms the home’s existing air leakage rate and whether air sealing is actually required (homes at or below 0.50 NACH are exempt from the air sealing requirement).
- Rebate verification: The post-test proves the 20% CFM50 reduction was actually achieved, not just claimed on an invoice.
- Safety screening: Homes with asbestos or vermiculite are disqualified from blower door testing — and therefore from the rebate program — until confirmed mitigation work is complete. A Combustion Appliance Zone (CAZ) test is also required to confirm that tightening the home will not create backdrafting or combustion safety hazards.
This is why only participating Xcel Energy contractors can submit rebate applications — a technician with the right BPI certification is trained to perform these tests correctly and safely. Self-installations or work done by contractors without the required certifications do not qualify for rebates.
How the Blower Door Test Connects to Your Insulation Rebate
Many Colorado homeowners are surprised to learn that the air sealing requirement isn’t just about the air sealing rebate — it can also affect whether your attic insulation and wall insulation qualify for their own rebates. Unless your home is already at or below the 0.50 NACH threshold on the pre-test, air sealing must be completed first, and the 20% CFM50 reduction must be demonstrated before the insulation measures become rebate-eligible.
In practice, most existing Colorado homes — especially those built before the 1990s — will have NACH values well above the threshold. That means a typical rebate project in the Denver Metro area involves both air sealing and insulation, with blower door tests bookending the entire project. Your contractor performs the pre-test, seals the identified leak points, verifies the improvement, then installs insulation. The post-insulation paperwork is submitted together as a bundled application.
Wondering how the math works out for your home? Use our insulation ROI calculator for a rough estimate of potential energy savings, then contact us or request a free quote to get a professional assessment.
What Happens During a Blower Door-Assisted Air Sealing Job
Here is a step-by-step overview of what a blower door-assisted air sealing project looks like when performed by a qualified Colorado contractor:
- Pre-test: The technician mounts the blower door fan in an exterior doorway, closes all windows and exterior doors, and depressurizes the home to 50 pascals. The CFM50 reading is recorded as the baseline.
- Leak detection: With the blower door running, the technician uses an infrared camera and/or smoke pencil to identify the primary air leakage points — common culprits include attic bypasses around plumbing and electrical chases, rim joists, recessed lighting canisters, and unsealed penetrations.
- Air sealing: The technician seals identified leaks using appropriate materials — typically spray foam, caulk, or weatherstripping — following industry-accepted practices for mitigating air leakage.
- Post-test: Another blower door test is performed after sealing is complete. The new CFM50 reading is compared to the baseline. A minimum 20% improvement is required for the air sealing rebate to apply.
- CAZ test: The contractor performs or acknowledges a Combustion Appliance Zone safety test to confirm that tightened air sealing has not created combustion safety issues with gas appliances.
Frequently Asked Questions About Xcel Air Sealing Rebates and Blower Door Tests in Colorado
Does every home need a blower door test to qualify for Xcel Energy insulation rebates?
Yes, with one limited exception: homes that already meet the 0.50 NACH (natural air changes per hour) threshold on a pre-improvement test may be exempt from the air sealing work and some testing requirements. However, pre-improvement blower door testing is still generally required to establish whether that exemption applies. The vast majority of existing Colorado homes, particularly older construction, will not meet this threshold and will require full pre- and post-testing.
What is a passing CFM50 number for the Xcel air sealing rebate?
There is no universal “passing” CFM50 number. The requirement is a 20% reduction from the pre-test baseline — whatever your home’s starting number happens to be. For example, a home starting at 2,500 CFM50 must reach 2,000 CFM50 or below to meet the standard. What matters is the improvement ratio, not the absolute number.
Can I perform my own air sealing and submit a rebate application?
No. The Xcel Energy air sealing and insulation rebate program requires that work be performed by a registered participating contractor who has a BPI-certified technician on staff. Rebate applications submitted by unregistered contractors or from self-installations are not accepted. This requirement exists in part because proper blower door testing requires specialized, calibrated equipment and training.
How long does it take to receive the Xcel Energy air sealing rebate after the project?
Rebate checks are typically issued within six to eight weeks after a complete application is received and reviewed. The rebate is issued directly to the customer (or an alternate recipient designated on the application). Your contractor will handle the application submission as part of the project, but Xcel Energy sends payment directly to you.
Does my home qualify for Xcel air sealing rebates if it has asbestos or vermiculite?
No. Homes with asbestos or vermiculite are disqualified from blower door testing — and therefore from the rebate program — until confirmed mitigation work has been completed to remove all hazardous materials. If your home was built before the mid-1980s and you suspect asbestos-containing materials may be present, this should be assessed before scheduling any rebate-related work.
Ready to Schedule a Blower Door Test and Air Sealing Assessment?
Insulation Nation is a participating Xcel Energy contractor serving the Denver Metro area and Colorado Front Range. Our BPI-certified technicians handle the full process — pre-test, air sealing, post-test, and rebate application paperwork — so you can focus on the savings rather than the logistics.
Call us at (720) 410-9414 to speak with a Colorado insulation specialist, or request your free quote online. You can also visit our Colorado service areas page to confirm coverage in your area, or browse our FAQ for answers to more common questions about the rebate process.