What Happens If HVAC Work Was Done Without a Permit Before I Bought the House? (IRC 2018)

Quick Answer

Unpermitted HVAC work discovered after purchase becomes the new owner's responsibility to resolve. Under IRC 2018 M1301.1, the code obligation runs with the building, not the person who did the work. You can be required to permit, inspect, and if necessary correct or replace unpermitted mechanical systems even if you had nothing to do with the original installation.

What M1301.1 Actually Requires

IRC 2018 Section M1301.1 establishes that all mechanical systems in residential buildings must comply with the code. The section does not distinguish between work done by a previous owner and work done by the current owner — the requirement applies to the building. When a jurisdiction becomes aware of unpermitted work, the enforcement obligation typically falls on the current property owner, regardless of when the work was done or by whom.

In practice, unpermitted HVAC work is discovered in several ways: during a home inspection as part of a real estate transaction, during a permit inspection for unrelated remodeling work, through a complaint from a neighbor or tenant, or during an insurance investigation following a fire or CO event. In each case, the jurisdiction will direct the current owner — not the previous owner — to address the violation.

The specific requirement once unpermitted work is discovered depends on the jurisdiction, but most follow a standard path: the current owner must apply for a retroactive permit, schedule an inspection of the unpermitted work, and make any corrections required by the inspector to bring the work into compliance with the code in effect at the time of original installation or the current code, depending on local policy. Some jurisdictions allow minor variances for well-executed older work; others require full current-code compliance.

The inspection challenge with retroactive permits for HVAC work is that critical elements of the original installation may now be concealed behind finished surfaces. The inspector evaluating the retroactive permit cannot inspect duct joint sealing, vent connector slope and clearances, or combustion air opening sizing if those elements are behind drywall. Some jurisdictions allow the inspector to evaluate visible aspects of the work and accept an engineer's letter certifying compliance for concealed elements. Others require selective demolition to expose critical items. The cost of the retroactive permit process — including potential demolition and repairs — can far exceed the original permit cost, which is why accepting a seller credit in lieu of a closed permit is often a poor deal for the buyer.

Why This Rule Exists

The code obligation runs with the building because the safety risk runs with the building. An improperly vented furnace installed by a previous owner creates CO risk for the current occupants just as effectively as one installed by the current owner. If code obligations could be extinguished by a property transfer, the inspection system would be meaningless — anyone could do unpermitted work, sell the house, and leave the problem for the buyer. Tying the obligation to the building rather than the installer protects subsequent owners and occupants.

What the Inspector Checks at Rough and Final

When a retroactive permit is issued for previously installed work, the inspection challenge is that some work may now be concealed. The inspector will evaluate whatever is visible: the equipment listing labels, vent connector condition and routing, combustion air openings, clearances to combustibles, gas piping, and filter access. For concealed work like duct sealing, the inspector may require the owner to open walls or provide documentation (photos, receipts) to demonstrate compliance.

If the inspector cannot verify concealed work, they have two options: require that it be exposed, or require that it be replaced with new work that can be inspected. The less documentation available about the original installation, the more likely exposure or replacement becomes necessary. Inspectors in this situation are making a risk-based judgment about whether the concealed work is likely compliant enough to leave in place.

What Contractors Need to Know

Contractors hired to remediate unpermitted work should document the existing conditions thoroughly before starting any work. Photographs, notes on equipment model and condition, and observations about venting and combustion air should all be preserved. This documentation becomes the contractor's evidence if disputes arise about what was found versus what was installed.

Do not assume that retroactive permits are straightforward. Some jurisdictions have specific processes for unpermitted work that differ from standard permits — different fees, different inspection sequences, or requirements to submit an engineer's letter certifying the work meets the applicable standard. Confirm the retroactive permit process with the building department before advising a client on costs and timeline.

What Homeowners Get Wrong

Buyers frequently discover unpermitted HVAC work during the home inspection process and negotiate a price reduction or seller credit rather than requiring the seller to pull and close the permit. This is a legitimate strategy — but the buyer needs to understand that taking the credit does not resolve the permit obligation. The permit obligation transfers with the property. If the buyer takes a $3,000 credit and then cannot close the permit without a $15,000 equipment replacement, the credit was inadequate.

The safer approach is to require the seller to pull the permit and pass inspections before closing. This puts the burden and uncertainty on the seller and ensures the buyer takes title to a clean property. Real estate agents often push back on this because it introduces closing delays, but it is the buyer's best protection.

Homeowners who discover unpermitted work after the sale sometimes try to ignore it, hoping it will never be discovered. This works until the next permit is pulled — at which point the inspector may become aware of the unpermitted work and require resolution as a condition of closing the new permit.

Insurance implications of unpermitted HVAC work are significant and underappreciated. Most homeowner's insurance policies require that regulated work be performed with required permits. A fire or CO event occurring near unpermitted HVAC work gives the insurer grounds to investigate the permit history. If the work was done without a permit and the event is connected to the unpermitted installation, the claim can be denied. Buyers who accept unpermitted HVAC work are accepting insurance exposure they may not fully appreciate. Requiring the seller to close all open permits before closing is not just about code compliance — it is about maintaining full insurance coverage from the first day of ownership.

State and Local Amendments

States using IRC 2018 — including Texas, Georgia, Virginia, North Carolina, South Carolina, Tennessee, Alabama, Mississippi, Kentucky, and Missouri — generally allow retroactive permits for unpermitted work. The process, fees, and compliance standard vary by jurisdiction. Texas local jurisdictions often charge a multiple of the standard permit fee as a penalty for after-the-fact permitting. Virginia requires that retroactive work meet the code in effect at the time of original installation, not necessarily the current code, which can make compliance easier for older work.

In IRC 2021, the enforcement framework was not significantly changed. The code obligation still runs with the building, and retroactive permitting processes remain locally administered. No change in IRC 2021 created a pathway to extinguish existing permit obligations through property transfer.

When to Hire a Licensed HVAC Contractor

If you are buying a home with known or suspected unpermitted HVAC work, hire a licensed HVAC contractor to inspect the system before closing — separate from the general home inspector. A licensed HVAC contractor can identify code violations that a general home inspector might miss and provide a realistic estimate of what it will cost to bring the work into compliance. This information is essential for negotiating the purchase price or requiring remediation before closing.

When a licensed HVAC contractor inspects unpermitted work as part of a pre-purchase evaluation, ask them to provide a written report documenting all observed conditions, estimated remediation costs, and their opinion on whether the work is likely to pass a retroactive inspection. This report serves two purposes: it is a negotiating tool with the seller, and it is the basis for the retroactive permit application if you proceed with the purchase and decide to permit and inspect the work yourself. A detailed pre-purchase inspection report that identifies the specific items the inspector will evaluate makes the retroactive permitting process faster and less likely to involve unwelcome surprises.

Common Violations Found at Inspection of Unpermitted HVAC Work

• Furnace vented into an attic space rather than through the roof — never permitted or inspected
• Gas line extended with unsupported steel pipe and flexible connections in prohibited locations
• Vent connector with negative slope, causing flue gases to pool in horizontal sections
• Combustion air openings entirely absent — mechanical room is completely sealed
• Return air ducted from the garage, which is prohibited by M1602.2
• Clearances to combustibles not maintained — wood framing within the labeled clearance zone of the furnace cabinet
• Equipment installed without a listing label or with label removed — cannot verify the appliance is listed for the application
• Condensate drain from high-efficiency furnace discharging onto the ground inside the crawl space