An old wall furnace safety check before Pasadena's first cold nights

Walk through enough older homes in Pasadena, Altadena, South Pasadena or Alhambra and you will see the same thing in the hallway: a gas wall furnace with a metal grille, sometimes original to the house. Many date from the 1940s through the 1970s, and some are older. They are simple heaters that can run for decades, but they burn gas inside a wall cavity, and age brings real risks.

Fall is the time to check one, before the first night in the 30s or 40s when you turn it on after months of sitting idle. Here is what a homeowner can safely look at, what a technician checks on a service visit, and how to tell when an old wall furnace has reached the end of its useful life.

A wall furnace burns gas in a small combustion chamber behind the front panel. Room air passes over the outside of a heat exchanger and comes back out the grille warm, either by natural convection or with a small fan. The combustion gases stay inside the heat exchanger and rise through a vent pipe that runs up inside the wall to a cap on the roof. Many older models use a standing pilot light that burns all the time.

The key safety idea is that combustion gases and room air never mix. When the heat exchanger cracks, the vent pipe separates, or the vent cap is blocked, combustion gases including carbon monoxide can spill into the room. That is why a wall furnace needs more attention than its simple design suggests. Older units also lack many of the safety controls found on modern furnaces, such as sensors that shut the burner down when venting fails, so a yearly inspection does more of the work that newer controls handle automatically.

Some signs mean the furnace should stay off until a technician sees it. A yellow, lazy or flickering flame instead of a steady blue one can mean poor combustion. Soot around the burner area or on the grille is another warning. A strong gas smell means leave the house and call SoCalGas from outside. Headaches, dizziness or nausea that ease when you leave the house can be a sign of carbon monoxide, and a CO alarm going off always means get out first and call for help.

Other symptoms are less urgent but still need attention: a pilot that keeps going out, a burner that lights with a loud whoosh or bang, or a fan that squeals. These usually point to a dirty pilot assembly, a failing thermocouple, a gas valve problem or worn motor bearings. A delayed, loud ignition in particular can stress the heat exchanger over time, so it is worth having it looked at before the coldest weeks of the year rather than living with it all winter.

A wall furnace with a cracked heat exchanger is not a candidate for repair. Neither is one with a badly corroded vent that cannot be safely reconnected. Parts for some older models are also getting hard to find. In those cases, replacement is the safe answer. Smaller fixes such as a new thermocouple, a pilot cleaning or a fan motor are often worth doing on a unit that is otherwise sound.

When replacement comes up, you have options. A new direct vent wall furnace vents through the outside wall and draws combustion air from outside, which keeps combustion separate from the room. A ductless heat pump mini-split can replace the wall furnace and add cooling at the same time, which many Pasadena homeowners appreciate during summer heat waves. We handle the permit where the city requires one.