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High-Efficiency Furnace Venting: Why You May Not Need a Chimney

replace chimneyLike furnaces, chimneys do not last forever. Time, household heating, and weather all take their toll. So, it’s no surprise that by the time you’re in the market for a new furnace, you’re also looking at chimney repairs. But here’s a piece of interesting news: you may not need a chimney at all. Today’s gas furnaces operate super-efficiently, so they use an entirely different type of furnace venting system.

Here's how it works and what options you have if you choose to forego chimney repairs.

How Does Pipe Venting Work?

Less efficient gas furnaces burn “hot” — between 275 degrees Fahrenheit and 350 degrees Fahrenheit — which is why you need a metal pipe and surrounding insulation for furnace venting. On the other hand, a super-efficient furnace will burn gas at just 85 degrees Fahrenheit to 150 degrees Fahrenheit. That’s cool enough that metal is not necessary. But there’s another factor at work here: moisture. The waste produced by a super-efficient furnace, though minimal, contains a mild acid condensate, which would corrode a metal chimney.

So, the vent pipe for a new, super-efficient furnace is small and made of plastic. And because it’s small and cool, rather than aiming straight up through a traditional chimney, the vent can run horizontally through the wall. (Similar to the vent for your clothes dryer.) And it's more cost-effective.

It could actually cost you more to repair your chimney than to invest in a new medium- or super-efficient furnace. Not only that, a new super-efficient furnace could reduce your energy costs by as much as 40%.

Super-Efficient Furnace Options

Efficiency is more than a vague concept. There is an industry rating called annual fuel utilization efficiency, or AFUE, that indicates how well a given furnace uses the energy you’re paying for — probably gas. Older furnaces can be as low as 60% efficient. That means you’re wasting 40%. Ouch! These furnaces are no longer made, but there are many still in use today. Mid efficiency furnaces, 78% to 82% AFUE, are available to replace older low efficiency units, and can be used with existing metal venting but are prohibited in brand new homes. 

A new super-efficient furnace will bring that up to 90%, and some models can deliver as high as 98% efficiency. If you're in the market for a new furnace, here are your high-efficiency options.

  • Modulating gas furnace. This is considered the best style because it continuously assesses and adjusts the heat output to precisely match your home’s heating needs and maintains an exact temperature setting. You are consistently comfy.
  • Three-stage gas furnace. This style “chooses” one of three heat output levels — 40%, 65%, or 100% — to keep your interior temperature constant.
  • Two-stage gas furnace. This one has settings for high and low, which can still do a pretty good job of consistently heating your home.
  • Single-stage gas furnace. You can still get a 90% or more AFUE rating with a single-stage super-efficient furnace.
  • Quiet Efficient Comfort. All of these furnaces have options for a variable-speed blower system to aid in summer cooling, reduce electrical consumption and reduce sound levels.

Any type of multi-state furnace will run less often, for less time, because it is making only small incremental adjustments. That means it will be quieter. It also means better humidity control. (If you have an air cleaner and/or furnace-mounted humidifier, they operate only when the furnace is running.)

Who knew gas furnaces had changed so much? Now that you know, it is well worth considering a super-efficient model for your next furnace. And you won’t have to give another thought (or dime) to your chimney.

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