HVAC FAQ

A fix may be as simple as relighting a pilot light or changing an air filter; however, not all home heating system issues should be tackled on your own. Get answers to common heating questions and learn what’s the best next step for you.

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Heating and air conditioning manufacturers require regular maintenance as a condition of warranty.  In other words, if your furnace has a mechanical failure during the warranty period, the manufacturer can choose not to honor the warranty if you cannot prove your furnaces’ maintenance record.  The Bonney Automatic Maintenance (BAM) programautomatically keeps computerized records of the tune ups performed on your furnace in case a warranty repair is required. 

As well, annual maintenance will keep your furnace in top operating condition.  Many utility districts, including our local utilities, promote annual service for the purpose of reducing unnecessary fuel consumption.  Reduced consumption means lower energy bills and more money in your pocket.  As well, annual maintenance increases the longevity of your equipment and reduced mechanical breakdown.  Both of these mean increased comfort and cheaper operation.  Read on to see why.

The purpose of a gas furnace is to heat the air in your home by burning natural gas or propane.  The flames and hot exhaust created by the burning gas are forced through a large piece of metal, the heat exchanger.  As the flame and exhaust gases pass through the heat exchanger it gets very, very hot.  Outside of the heat exchanger, the blower motor blows air from your home past the heat exchanger and the air is warmed and returns to the home.  As the furnace heats and then cools, when it is off, the heat exchanger expands and contracts.  Eventually, the expansion and contraction of normal operation will cause the heat exchanger to crack.  The time it takes for the heat exchanger to fail depends on the quality of the furnace and the quality of the installation by the heating and air contractor.

Once a crack occurs, several negative consequences can occur.  First, the flame can be pushed backwards, out of the heat exchanger and into the furnace cavity.  This condition is called “roll out”.  Most furnaces are equipped with a safety sensor that detects roll out and turns off the gas valve stopping the flame.  However, if the safety circuit is not maintained properly it may not identify roll out which could cause a fire in the furnace and potentially spread outside the furnace; a very dangerous situation.

A second consequence of a cracked heat exchanger is that the flame will not burn properly.  A flame that does not burn properly can create soot and other harmful by-products including carbon monoxide (CO).  Carbon monoxide is an odorless, tasteless, invisible gas that reduces the lungs ability to absorb oxygen (O2).  Low levels of carbon monoxide can cause headaches, nausea and lethargy.  High levels of carbon monoxide will cause death.  Standard CO detectors will only alert at pre-set levels for the purpose of immediate evacuation to avoid death.  Standard CO detectors are not designed to detect low levels of carbon monoxide poisoning and therefore do not prevent symptoms from low level poisoning.

A third consequence of a cracked heat exchanger is the potential to introduce carbon monoxide into your home.  Every furnace has the potential to produce some level of carbon monoxide.  When the furnace operates properly, combustion gases pass through the heat exchanger and vent safely out of the house.  When a heat exchanger cracks, the venturi effect can bring some amount of exhaust gas into the home.  The amount of gas and level of carbon monoxide depends on a number of factors.  But, any level of carbon monoxide in your home can cause poisoning and possibly death.

For safety reasons, it is the standard of the heating and air conditioning industry to disable a furnace that has a clearly determined crack in the heat exchanger.  The heat exchanger or the furnace must be replaced before resuming operation.  Because of the serious consequences of a cracked heat exchanger, a quality heating and air service contractor will not tell you that your heat exchanger has a “possible” crack, but will prove it to you through one of a number of available techniques.  If a service technician has told you that you have a cracked heat exchanger, Bonney is ready and able to give you a FREE second opinion with conclusive proof.  Click here to request an appointment for a thorough evaluation of your furnace’s heat exchanger.

There are several reasons why a furnace may turn on and off repeatedly, a situation called “short cycling”.  The longer a furnace runs, the more efficient it operates, using the least amount of gas and electricity.  When it short cycles, not only do utility bills rise, but so does the possibility of mechanical breakdown.  More importantly, however, is the significant reduction in the life of the furnace.  As you can see, short cycling is an expensive problem.

Every furnace has a control system and a safety system.  The control system includes the thermostat which tells your furnace when to turn on and off.  One possible cause of short cycling would be a thermostat with a mechanical deficiency or improper settings.  This problem can be alleviated by using the correct thermostat, with the installation options and programming set correctly.

The furnace safety system is designed to stop the operation of the furnace when it operates beyond specific safety limits.  In most furnaces, many safety system components will automatically reset when the unsafe situation is relieved.  The reset allows the furnace to operate again until the safety limits are exceeded, at which point it stops the furnace.  If the problem that caused the safety system to turn the furnace off isn’t repaired, the furnace will continue to short cycle.  Other safety system components must be manually reset by a technician after the cause for failure has been corrected.  If a manual reset safety has failed, your furnace may not operate at all, or the blower motor may run continually, blowing cold air throughout the home. 

Sometimes, short cycling isn’t easily identified because the blower fan may continue to run, but the heat works intermitently.  The safety system may simply close the gas valve so that the furnace will stop heating.  Once the furnace cools, the furnace ignites and begins to heat again, all while the blower fan continues to run.  If the air temperature blowing from the registers is inconsistent, the unit is likely short cycling.

Annual furnace maintenance will identify short cycling issues and provide money saving solutions.

The filter in your heating and air system is designed to remove particles from the air traveling through the heating system and re-circulated into your home. 

The filter provides two benefits.  First, the filtered air is healthier.  Particles in the air include dead skin cells, animal dander, pollen, mold spores and bacteria.  The style and quality of your filter will determine how effectively these particulates are removed.  (Click here for more information on air filtration and purification.)  Filtered air means less allergens, less irritation, and less dusting.

Second, the filter protects the heating system.  A dirty heater is an inefficient heater.  A dust layer as little as 1/16” on the blower wheel can reduce furnace efficiency by as much as 25%; causing a significant increase to your utility bills.  Furthermore, a dirty filter, or the wrong “high efficiency” filter, reduces air flow to the heater.  Reduced air flow is a primary cause of short cycling which increases utility bills and decreases the life of your heater (see the question about short cycling above).

The frequency of filter replacement depends on how much you use your system, the presence of pets, and the style of filter.  For most people that use 1” paper filters, replacement should occur every 30 days.  Thicker filters, 2” – 4” can be replaced less frequently, every 3 – 6 months.  Some high quality, 4” – 5” filters can be replaced yearly.  Never use 1” “high efficiency” paper filters as they create substantial reduction in air flow causing short cycling.

Many customers have found that washable filters provide adequate filtration without repeated expense.   Because the lifetime of the filters is frequently over 10 years, a washable filter is a good investment.  Depending on the characteristics of your home, most filters can be washed every 30 – 60 days.  Be sure to wash your filters with light detergent spray such as 409 and a strong stream of water.