(Not) A Lot of Hot Air
By Mark Clement
How many of us really think about our HVAC system and its optimum performance? I mean really think about it. Sure, we change the filters, although not as often as we should, but as long as the air comes out, we’re comfy, and the utility bill is less than outrageous, then we focus on our crown molding, decks, landscapes and cabinets. Those are the things we can see, touch, cut and care for.
But the reality is we all have to think about it at some point. Lots of people have to think about it during an “oh crap!” moment, when the weather is snowing or searing, and there is no air coming out. That happens all the time. With a system so important, panic is not the proper ingredient for making good decisions. Stuff will go wrong.
What’s more, the “oh crap!” moment is usually followed with an “it costs how much?!” moment. That’s why this isn’t one of those seasonal “save money on your energy bills” articles.
Nope. This article is a check-down of how to prevent that aforementioned—and usually unbudgeted—moment. The payoff is that in the process, you’ll be able to see the signals and plan ahead. Oh, and I love this one: You can find out how much money your old system has been burning and sending up the chimney.
The heart of the HVAC system is the furnace or air-handler which, where we live, is typically in the basement. Its burners provide the heat and its blower motor pushes and pulls the air (hot or cold) through the house’s circulatory system.
Like any person’s heart, this unit—which should be 80,000-100,000 BTUS for a typical 2,500 square foot home—has a lifespan, which is somewhere around a quarter century.
You can check, or at least try to check, the age of your system by removing the cover plate and looking at the labels. There may be an indication of an installation date or a service call that can guide you. If there’s no labeling or the ink has faded, you can probably bet that when this unit was being installed in your basement you were in high school, going on your first date, or learning to ride a bike.
One way to equip yourself with some data—labels or not—about your system is to check the heat exchanger, right above the burners. With the faceplate removed, shine a flashlight and look for rust. Rust is a sign of age and decay.
Most of the action in the heat exchanger happens right above the burner, so this is a big wear area. And since the unit can be rusting from the inside out—and the outside in—don’t be fooled by “a little rust” on a three-decade old system.
A unit that’s 20, 30, or if you’re very lucky, 40 years old was designed to deliver at best 70-percent efficiency. That means for every dollar of natural gas you purchase to power it, 30 percent goes up the chimney—under perfect conditions.
Problem is the science of air movement, never mind building codes, government regulation and developments in technology, those conditions are rarely ideal. So assuming the unit is Goldilocks-end (not too big, not too small, but just right for the house), under-sized ducting could be throwing away even more energy, taking a 70-percent efficiency unit down to 50 percent. Not only does this shorten the life span of the unit, but you’re literally burning 50 cents of every dollar you spend heating and cooling.