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Gas Furnace

A Gas Furnace Only Provides Heat. You Will Also Need a Heat Pump or AC.

York Gas FurnaceThis means that a complete system including gas heat is going to consist of three major components: the furnace which is usually located in the attic, crawlspace, basement, or occasionally in a closet in the house; an outdoor unit which will be an air conditioner or heat pump; and a coil which is usually a box attached to the furnace so it all looks like one piece. There are variations, but most gas heating and cooling systems will have these three parts.

People who have been around both gas heat and a heat pump know that gas is a different kind of heat. I guess the word used most often about it is that it’s a “warmer” heat. In fact, it is warmer as it comes out of the registers. Follow me here: a gas furnace will put out heat at a high constant temperature until your house reaches the thermostat setting. That’s the nice, toasty warm feeling typically associated with a gas furnace. A heat pump, on the other hand, puts out heat that is much closer to the actual thermostat setting and depends very much on the temperature outside. If the thermostat says 70 degrees, that’s what the heat pump is trying to put into your house though it struggles when it’s really cold out. There is a system that takes advantage of the best of both worlds called “dual fuel” or a hybrid system.

Keep in mind that if you don’t already have natural gas in your neighborhood, it can cost a fortune to get it run to your house. You can use propane but the economics of heating this way will be different than with natural gas. It can still be cost effective and more comfortable so check with us if this is something you’re considering. We can run the numbers for you if you’re in the market for a new system.

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Important Things to Know About Gas Heat

    Carbon Monoxide Alarm

    Burning Gas

    Gas burns in a process known as combustion and gives off by-products including water and carbon monoxide (CO). CO is deadly and particularly dangerous because it’s colorless and odorless. You’ve read the articles and have heard the news reports about whole families that have died from carbon monoxide poisoning usually while they slept. Every year it happens when people burn fuel in a dangerous way, such as using kerosene heaters or charcoal fires indoors, or when there is something very wrong with a furnace. Luckily there are simple, inexpensive detectors for carbon monoxide. Everyone who heats anything by burning a fuel, including gas stoves or water heaters, or has an attached garage should have at least one carbon monoxide detector inside their home.

    Furnace Design

    A gas furnace is designed by engineers who live in a technical center (well, they don’t actually live there. Most of the ones I know work there and like to hang out there a lot so they may as well live there.) They take all of this into consideration when they develop a very efficient way for the furnace to deal with these by-products ASSUMING THE SYSTEM IS INSTALLED CORRECTLY BY A QUALIFIED HVAC CONTRACTOR. These systems are the chimney, or vent pipe, and the fresh air intake. They do two different jobs.
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    Vent Pipes

    A vent pipe is designed to send these by-products outside. It looks pretty simple and straight-forward – put a metal pipe on it and make sure the other end of the pipe goes outside. But it’s not that simple. There are strict rules about what the vent pipe can be made of, how long it can be, how many times it can bend, what the rise has to be, how big around it can be, how small it has to be, etc. The gasses don’t just go up the chimney or vent pipe because they want to or because they know they’re supposed to go outside. All of this is done to support the physics we’re using to get the chimney to start to draft. It’s part of our job as HVAC contractors to make sure that’s happening. If it doesn’t, those gasses roll back into your house and you run the risk of carbon monoxide poisoning.

    Fresh Air Intake

    The second system is the fresh air intake. In order to get a good clean fire burning, fuels require air and lots of it. It is critical that a gas furnace gets all the air it needs to combust cleanly and safely. Cleanly because if it isn’t burning clean it uses more fuel which drives up your gas bill and dirties the inside of your furnace which means it burns even less cleanly which means your bill goes up some more and the cycle builds. Safely because that fire is going to find air one way or another. If it doesn’t have a dedicated source of air, such as another pipe that’s bringing in fresh air from outside, it can “roll out,” or reach outside the equipment to find air. We’ve seen this many times on gas water heaters in particular. People store a bunch of stuff around it or change the door from a louvered door to a solid door because it looks better, and the water heater is no longer getting all the air it needs. The flame “rolls out” of the door at the bottom and burns the side of the water heater and potentially whatever is packed around it. The same thing can happen with a furnace.

    Evidence of a Flame Roll-Out

    Evidence of a flame roll-out. The front of the water heater is actually burned.

    All this boils down to a couple things.
    • Have at least one carbon monoxide detector, preferably one with a digital display.
    • Do not pack anything around any gas burning appliance.
    • Do not decrease the size of the room that the appliance is located in without talking to us first about whether it’s safe to do so.
    • Do not change the pipe or block it anyway, not even with an animal screen at the end if you haven’t asked us first if it’s okay.

    Gas appliances are not something for amateurs or for people who watched their cousin’s uncle’s brother-in-law put one in. It’s a wonderful source of heat but installation and maintenance must be left to the skills of a well-qualified, professional HVAC Contractor. Like us.

  • Comparing Furnaces

    Like heat pumps and air conditioners, there are things to compare on proposals you receive to replace or add a furnace.



Efficiencies for fuel burning appliances like furnaces are displayed as AFUE, or Annual Fuel Utilization Efficiency. The higher the number, the more heat the furnace is capable of pulling out of each unit of fuel that’s going in. High efficiency furnaces can have AFUEs of 97 or 98% which means almost all of the fuel going in is being converted to heat. They can also go as low as 80% which means 20% of your fuel dollars are being wasted. Think carefully about this ongoing cost when deciding on new equipment.


Size of the Unit

As with air conditioners and heat pumps, the size of the furnace needed for your house is going to depend on a lot of the physical characteristics of your home. A qualified HVAC Contractor will need to gather some information about your house such as its size, the number and type of windows it has, what the insulation level is in the attic, the floor, and the walls, what direction the house faces, etc. All of this information gets entered into a program called a Manual J, or a Load Calculation, which will tell the contractor what size the furnace needs to be to meet the heating needs of your home.

To go just a little bit deeper, a btu is a measure of how much energy you can get out of a specific quantity of a specific fuel. In regular people terms, one btu is equal to about the amount of heat you get out of burning one wooden match. Typical values for gas furnaces will run between 60,000 and 120,000 btus, or a whole pile of matches!


Qualifications of the HVAC Contractor

This is probably one of the most overlooked items and is probably more important than anything else you need to consider. You are about to replace one of the most expensive appliances in your home and it’s going to be with you for at least the next 10 years if it’s any good. You are going to depend on it to keep you warm in the dead of winter. It will cost you money every single day it’s on (a lot of money if it isn’t very efficient.) You are going to depend on the fact that it will operate safely. With all of that on the line, doesn’t it seem logical that you should take at least a little time to check the qualifications and references of the company you are trusting with this installation?

According to the NC State Board of Examiners of Plumbing, Heating, and Fire Sprinkler Contractors, there are four places you should check when you have your list of possible contractors narrowed down to just a couple: the Better Business Bureau, your city or county building inspection department, the Consumer Protection Section of the Department of Justice, and the licensing board itself. For contact information for these agencies, click here.

Most people don’t have to replace or add a system more than once or twice in their lives. It’s not something that comes up in conversation everyday so how to go about doing it to get the best system for your home is not common everyday knowledge. Take advantage of the tools and references that are available to help you with this decision. Your wallet, maybe even your life, depend on you making a well-educated choice.



Most new furnaces will come with a parts warranty from the manufacturer. It’s usually five or ten years of coverage. If something breaks in that time period, they will provide the replacement part at no cost. However, this type of warranty does not cover labor. Often it isn’t necessarily the cost of the part that creates the big repair bill but the time it takes the technician to physically get to it, take the broken part out and replace it with the new part, and then replace all the other parts he had to take out to get to it in the first place.

For most systems, there is another type of warranty you can purchase. It’s generally referred to as an Extended Warranty and can cover additional years of parts, labor or parts, and labor for your system. Considering how long you might own your furnace and that repairs tend to get more expensive as the equipment ages, buying an extended warranty is definitely something you should consider.

If you have any questions, need any more information about gas furnaces, or anything else related to heating and cooling for your home, please CONTACT US.