Archive for the ‘Gas Heating’ Category

Gas Furnace Or Tiger By The Tail?

Monday, May 8th, 2017

Gas furnaces are among the safest HVAC equipment in use anywhere, if all conditions are right.

Because of widespread and common use, building owners take for granted reliable and safe operation.

Let’s compare an electric furnace to its gas-fired counterpart.

Electric Furnaces

Electric furnace safety devices typically include circuit breakers to prevent fires due to short-circuit faults. An air flow switch prevents electric furnace operation when air flow through the furnace heating elements is insufficient. A simple high-temperature cutout serves to kill control power to power contactors if for whatever reason the air flow switch fails or has been tampered with.

The operation of electric heat is simple. Need heat? Turn it on. Don’t need heat? Turn it off.

Gas Furnaces

Gas furnaces feature sophisticated gas valves, combustion air blowers, igniters, flame detectors, high-temperature cutout sensors, complex flame safeguard electronics, a flame rollout sensor, and two air pressure sensors.

tiger by the tailIf all equipment and controls are in proper working order and you need heat, then a complex purge-ignition-combustion sequence starts up. If there are no spider webs, no cracks in the heat exchanger, flue vent is clear, gas pressure regulation is right, then the heat comes to the conditioned space.

What can go wrong? Plenty. There is a good reason for the sophisticated electronics and safety devices. These devices and electronics are in place to protect persons and property from fire, explosions, and carbon-dioxide poisoning of persons within the conditioned spaces.

Leaking heat exchangers can introduce carbon monoxide (CO) into the airstream. CO is a colorless, odorless, deadly gas known as the silent killer. According to the American Council on Science and Health, carbon monoxide kills more Americans than mass shootings.

As though there is nothing more to worry about, think again, this time on the issue of flame rollout. The Fire Science Training Institute wants building owners and consumers to know the danger of flame rollout.

Flame rollout is the term commonly used to describe a fuel gas combustion process occurring outside the normal combustion area of a gas appliance. Any gas combustion not properly confined to the appropriate area could obviously have serious consequences. Electrical wiring, gas valves, and combustible materials located near appliances may be compromised by flame rollout. Flame rollout can cause gas control valves, usually made of metal alloys with relatively low melting points, to fail structurally. Such a failure can be responsible for the release of a devastating volume of gas with a ready source of ignition. – Fire Science Training Institute: Understanding Flame Rollout In Gas Appliances


If the HVAC unit in question has direct-expansion refrigeration, then the electrical service to that unit (typically a rooftop unit) will be adequate to power an electric heater.

In the case of chilled-water systems, electrical service to the air handling unit is only adequate for the fan motor(s) and controls. One solution: Replace a gas furnace with a heating-water coil fed by a standalone gas-fired heating water boiler.

Wish to discuss any of the above issues? Contact us anytime for an appointment.

John White

Rockwall Controls Company, Inc.

(972) 771-3514