Frequently Asked Questions

High Demand Heating likes to keep our customers in the know. That’s why we’ve put together some of our most frequently asked questions.


There are several sources of information you can check: the documentation that came with your furnace; the HVAC contractor that installed or services your furnace; your furnace manufacturer; or a furnace filter vendor.
Check the documentation that came with your furnace. Recommendations vary based on a number of factors: the type of filter that you use, how many pets you have, whether anyone in your home has allergies, etc. If you use disposable fiberglass panel or electrostatic panel filters, you should change them anywhere from once a month to once every three months. Pleated filters generally last from 3 months to a year.
Furnace manufacturers put inexpensive fiberglass filters into their furnaces to remove airborne particles that might damage the fan and the heating coil. Particle buildup can also decrease the efficiency of your furnace, as the furnace has to work harder to pull air through the intake. More expensive filters can also improve the air quality in your house by removing pollen, bacteria and mold spores from the air. This is especially important if you or someone in your family suffers from allergies.
You have two choices – you can replace your furnace before it breaks down, or wait till after it breaks down. If you replace it before it breaks down, you can take time to shop for the best deal, and install it on your own timetable. If you wait till after its breaks down (probably on the coldest day in the winter) you are usually in an emergency situation and need to replace it immediately. You may not be able to get the best deal and may have to settle for the first furnace you can get. Therefore, you may want to consider replacing your old furnace before it breaks down.

The average 80% standard oil or gas furnace lasts 18 years. Most high efficiency 90%+ furnaces only last 12 years due to their longer run times and design characteristics. It makes sense to have your furnace checked by an HVAC professional every few years. This is especially true for older units. Once you get past the life expectancy of the unit consider planning for a replacement unit. These symptoms can indicate a furnace should be replaced

  • Frequent pilot light outages
  • Delayed ignition
  • Yellow flame or wavering flame
  • Excessive soot or corrosion
  • Too much or too little heat
  • The smell of sulfur or burnt eggs
Your forced-air heating system can perform more efficiently if you…

  • Inspect filters once a month and replace as needed during heating season
  • Inspect fan belts for cracks
  • Make sure vents and air return vents are clear of obstruction
  • Check chimney and venting systems once a year for secure fittings, leaks, and no corrosion or damage
  • Keep area around furnace clean and clutter-free
  • Do not block the source of furnace combustion air by enclosing furnace is a small closet or by making the room it is located in too air tight
Proper sizing is the most important thing in replacing a furnace. Bigger isn’t better. Smaller isn’t cheaper. The best comfort and efficiency is through a properly sized furnace. If the furnace is too small it won’t keep the house at the desired temperature when it is cold outside. If the furnace is too big it heats the house too quickly and than shuts off. This results in hot and cold swings in temperature in the house.

To properly determine the correct size for a furnace, the dealer should do a heat loss calculation. This is sometimes called a Manual J calculation. If the dealers will not do this calculation, you may want to consider a different dealer for your furnace.

Furnaces prior to 1990 were 55% to 65% efficient. The standard furnaces today are 80% efficient. High efficiency furnaces can be up to 97% efficient. A high efficiency furnace will generally cost more to install, but will save about 15% of the heating bill as compared to a standard unit. Have your furnace dealer show you a comparison of the differences in purchase cost and operating cost before making a purchase decision. If your furnace is more than 15 years old, a new furnace will probably be more efficient and save money.
There have been a number of improvements in furnace technology:

  • Two stage or multi speed burners that provide more comfort and efficiency than single stage burners
  • Hot surface or spark ignition – eliminates pilot light
  • Electroic blower control reduces cold drafts at start up
  • Electronic thermostats are more accurate then mercury bulb thermostats
  • Direct drive motors for dependable air flow
  • Multi-speed direct drive motors work in conjunction with multi-stage burners to improve air distribution temperature
  • Zoned heating increases the comfort level and increases the energy efficiency of the house
  • Direct venting through low-temperature piping allows elimination of chimney

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