Do You Own an Inefficient Furnace?

You are reading this article because your wondering how old, or how inefficient your old furnace/heater is, and whether or not it has a big carbon footprint. I will specifically talk about natural and propane gas fired furnaces and heaters. Some people call them a furnace, some call them a heater, if they don't have the word condensing in front of them I call them inefficient. If your furnace does not make water when it operates, then it is inefficient.

In California and according to PG&E: (Pacific Gas & Electric) Company

Burning one Cubic foot of natural gas will produce 13.446 lbs of carbon dioxide. All furnaces will produce carbon dioxide because it is a byproduct of burning natural gas. Go out side and clock your PG&E meter while the furnace or heater is on for a full minute then multiply that figure by 60 minutes to get your total cubic feet per hour. Multiply that number by 13.446 and you can see how much carbon dioxide that your furnace produces in one hour.

If your furnace does not remove 90% or more of the heat from the total number of cubic feet of natural gas burned before the gas is vented out of the furnace, then it is absolutely inefficient!

You ask "how can I tell if it's removing at least 90% of the heat" from the burned gas that is vented out of the furnace?

This is the easy part. Simply look at the furnace exhaust pipe - if it is metal, about 4-5" in diameter and it gets really hot, hot enough to burn your hand after its been operating for a while, the furnace is inefficient. It's a gas hog, a gross polluter in my book. In comparison to a 98% efficient furnace. Your old furnace is like a car that gets 14 miles to the gallon when it could get 30. Some condensing furnaces have a rating of 98% AFUE (look it up) which means it removes 98% of the heating value from the burned fuel before it is vented out of the furnace.

In terms of the amount of useless carbon dioxide the 80% furnace produces, a furnace that has an AFUE of 98% delivers almost 100% of the heat value of the fuel into your home as a result of producing that 13.446 lbs co2 per cubic feet consumed. Its wasted co2 production factor is only about .446 lbs per cubic foot consumed because it only has one heat exchanger, condensing furnaces have two..

In contrast an 80% AFUE furnace with a metal vent pipe is not only inefficient in terms of heat value delivered to your home, but it is extremely inefficient in terms of producing heat as a result of producing carbon dioxide or Co2. You can do the math your self and see that for every cubic foot of natural gas your old furnace consumes. You are producing more wasted carbon dioxide than a condensing furnace would at a rate of about 3lbs per cubic foot of natural gas consumed. More Co2 than a condensing furnace would, that gives you no direct benefit, and which costs you money while contributing to global warming.

Your furnace uses fuel at a much higher rate than it should and it produces wasted carbon dioxide at a much higher rate than it should. Your furnace has to have a metal vent pipe because of the temperature of the exhaust gases. A condensing furnaces exhaust gas is cooled so much that the vent pipe has to be made of PVC because they make water when they run.

In the old days a furnace with an 80% AFUE rating was considered to be high efficiency and many of them came with a sticker that said high efficiency on them. But once the first Condensing Furnace came out and natural gas consumption started to soar - the 80% furnace with a single pass heat exchanger became inferior in terms of energy efficiency.

If your using an old furnace with a metal vent pipe, then you are behind the times. It is sort of like driving one of those great big long American made cars of the late 70's with an enormous engine, during the gas shortages. A condensing furnace is like driving one of today’s hybrids. Extremely energy efficient, saves gas and low pollution.

A condensing furnace is safer too, in that most condensing furnaces have totally enclosed combustion chambers which protects from total flame roll out in the case of a failed induced draft blower motor. I am 100% sold on condensing furnace technology, so much that I don't provide 80% low efficiency furnaces as one of the products we carry, you won't find any links to low efficiency equipment on our website. As a result our customers get longer heat exchanger warranties, limited lifetime warranties on a condensing furnace vs. 20 year limited warranty on an 80% furnace.

Take a look at your utility bill and see how many therms of natural gas you consumed last month, how many therms were in the base line usage and how many were in the over base line category. If you’re over base line usage is higher or close to your base line usage, it's time to change that old gas furnace out to something more modern.

The best way to understand the waste your old furnace produces, is to imagine that you run your furnace for one hour this morning trying to heat your home. For the first twelve minutes of that hour your system does not blow any of its heat into your home, but blows it to the outside and you do not feel any of the warmth that you are spending money on. That’s essentially what you are doing by utilizing an inefficient furnace. By tomorrow that 12 minutes will be 24 minutes of two hours, 36 minutes of three hours and so on. At some point the money you waste in using that old furnace will pay for most, if not all of a new condensing furnace.