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FURNACE PROBLEM · DIAGNOSIS GUIDE

Furnace Making Strange Noises — Decode the Sound

Different noises point to different problems. Use this guide to figure out what's happening before you call.

Since 1999NJ Lic #19HC0010870024/7 DispatchSame-DayNewton, NJ

Some Sounds Need Immediate Action

Banging or booming at startup = delayed gas ignition, which is a safety concern. Stop using the furnace and call us same-day. Rumbling or signs of cracked heat exchanger = carbon monoxide risk. Get a working CO detector near sleeping areas if you don't have one.

Why It's Happening

Decoding the Sound

1

Banging or booming at startup

Delayed ignition — gas builds up before lighting, then ignites with a small explosion. This is a safety concern. Stop using the furnace and call us same-day.

2

Rumbling that gets louder over time

Often a dirty burner, sometimes a cracked heat exchanger. Cracked heat exchangers are a carbon-monoxide risk — get the furnace inspected immediately.

3

Clicking that won't stop

Failing ignitor or control board trying to start. The system is going through its startup sequence repeatedly without success.

4

Whistling or whining

Often a duct or return-air issue (undersized return, closed registers, partially blocked filter). Less serious than the others but worth fixing — it's costing you efficiency.

5

Squealing or grinding

Blower motor bearings are failing. Replace the motor before it seizes and damages other components. $400-$700.

6

Rattling

Loose panel or duct connection. Usually cosmetic but easy to fix.

Safety

Carbon Monoxide Risk

Banging or rumbling noises can indicate cracks in the heat exchanger, which can leak carbon monoxide. If you don't have a working CO detector near sleeping areas, install one today — this is the most important $20 you can spend on home safety.

If your CO detector goes off, leave the house and call 911. Don't try to ventilate or wait it out.

27 yrs
Since 1999 in Sussex County
24/7
Real techs answer — not voicemail
NJ Lic
HVACR #19HC00108700
$0
Diagnostic fee waived when you book repair
★★★★★

Loud banging at startup. They came out, found delayed ignition due to a dirty gas valve, cleaned it, and the noise stopped. Half what another company quoted.”

Greg P. · Stillwater, NJ

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98 Morris Turnpike, Newton NJ · NJ HVACR Lic #19HC00108700 · Since 1999

At Constant Air, we specialize in delivering high-quality heating, ventilation, and air conditioning services that keep your home and business comfortable all year round.

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