Find out which air path was changed

“Combustion-air duct” can mean an outdoor opening serving the equipment room or a pipe connected directly to a furnace. Those are different arrangements. The technician needs to identify the installed furnace, its approved air source, other fuel-burning appliances nearby, and the change made during the repair.

Ask for a plain explanation: “Where should this furnace get its air now, and what confirms that this setup meets its instructions?” Do not accept “it stopped freezing” as the entire answer. That describes a result, but leaves the safety and installation questions open.

We recommend addressing the original freeze problem and the altered air supply together. Otherwise, one visit may restore the opening while another repeats the same workaround the next cold night.

What the follow-up should establish

Ask the technician to explain whether the freezing involved the intake, exhaust, condensate drain, or something else. Request the model instructions that apply, the inspection and operating findings, and the correction that addresses the cause.

Useful questions include whether the installation matches an approved direct-vent or room-air arrangement, whether the equipment room has the required air supply, and whether nearby exhaust fans affect that assessment. These are questions for professional evaluation, not instructions to test the furnace with doors open or fans switched on.

If the change was made by the original installer, give that company a chance to explain its documented basis. If the explanation remains unclear, an independent qualified assessment is reasonable. Do not infer workmanship or warranty responsibility from an online description.

While this is being resolved

If the home cannot stay warm enough without this furnace, ask about the repair timing and arrange a suitable place for the household to stay if needed. Do not trade an unverified combustion setup for overnight heat.

Your next action is to request a qualified follow-up specifically covering both the closed air opening and the freezing that led to it.