Field note from Cainen Bedsaul, co-owner and InterNACHI® Certified Professional Inspector with TMK Inspections.
During a recent Philadelphia home inspection, a gas furnace started normally when I raised the thermostat. The burners ignited, and I continued observing the equipment until the circulating blower came on. That is when I heard an unusual noise from one of the burner chambers.
A home inspector should not label a heat exchanger as cracked without appropriate confirmation. The sound and operating behavior were concerning enough, however, that I documented what I observed and recommended evaluation by a qualified HVAC professional before the buyer moved forward.
What happened after the inspection
I shared a short video of the furnace operation with an experienced HVAC technician. He agreed that the condition warranted prompt investigation. After evaluating the furnace in person, the technician confirmed a cracked heat exchanger. He also reported that a rollout safety switch had been bypassed.
That second finding made the situation especially serious. Furnace safety controls are designed to interrupt operation when unsafe combustion conditions occur. Bypassing a safety device can allow equipment to keep running even when the system should shut down. The HVAC technician recommended replacement of the furnace rather than continued operation.
Why a cracked heat exchanger matters
The heat exchanger separates the furnace’s combustion gases from the air distributed through the home. A crack or other failure can create a pathway for combustion products to enter the air stream. Actual risk depends on the location and extent of the damage and on how the furnace is operating, which is why a qualified HVAC diagnosis is essential.
Carbon monoxide is colorless and odorless. Homeowners should maintain working carbon-monoxide alarms in the locations recommended by the manufacturer and applicable local requirements. A home inspection does not replace alarm maintenance or professional furnace service.
What a home inspection can—and cannot—determine
A standard home inspection is a visual, non-invasive evaluation of accessible systems and components. Inspectors operate installed equipment using normal controls and observe its response, but they do not dismantle sealed furnace assemblies or perform the specialized testing used by an HVAC contractor.
In this case, the value of the inspection was not an unsupported diagnosis. It was careful operation, continued observation after ignition, recognition that the sound was abnormal, clear documentation, and a recommendation for the right specialist. The subsequent HVAC evaluation supplied the confirmation.
Questions buyers can ask about an older furnace
- How old is the furnace, and is service documentation available?
- Did the inspector observe normal ignition and blower operation?
- Were any covers, switches, wiring, or safety controls visibly altered?
- Did the inspector recommend HVAC evaluation before settlement?
- Are carbon-monoxide alarms present and operating?
No single observation should be taken out of context. Rust, age, unusual sounds, flame disturbance, repeated cycling, or visible modifications may justify further evaluation, but an HVAC professional should make the final equipment diagnosis and repair recommendation.
Why careful observation matters
A furnace that produces heat is not necessarily operating safely. Major systems deserve more than a quick on-and-off check. At TMK Inspections, we take time to observe accessible equipment, explain material concerns in plain language, and provide photo-rich reporting that helps buyers and agents make informed decisions.
Learn more about our residential home inspections, review our Philadelphia-area service areas, or request an inspection. You can also call or text Cainen at (610) 620-5857, Tom at (484) 678-4464, or Chris at (215) 932-4487.
This article describes a real inspection sequence with identifying property and client information omitted. It is general information, not a diagnosis of any other furnace.