Furnace Oversizing Facts

by Trey Muffet on August 16, 2010
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Oversizing of mechanical equipment has been a standard of installation for many years, but thanks to a growing emphasis on building efficiency and home performance, oversizing is (hopefully) seeing the end of its days.

Common reasons for oversizing include failure to perform the proper load calculations; compensating for leaky ducts; or contractors protecting themselves from callbacks during extreme weather. Whatever the reason, oversizing is always a no no—even for high-efficiency equipment. But there are many misconceptions floating around about why oversizing is bad, and many people lack a clear understanding of what’s really at stake.

Recent studies show that furnaces with an Annual Fuel Utilization Efficiency (AFUE) rating above 0.75 can be sized up to five times the load without a significant drop in efficiency. (Keep in mind, however, that the average load throughout the year is much lower than peak loads calculated by Manual J.) For example, let’s look at a 95% two-stage furnace. In second stage, the 60,000 BTU/h furnace will operate at steady state 95% efficiency when loads reach as low as 12,000 BTU/h. First-stage capacity of 39,000 BTU/h can operate efficiently for loads as low as 7,800 BTU/h.

Though efficiency may not be affected by oversizing, here are a few reasons why oversizing is still an issue:

1. Furnace prices increases with size, so installing the smallest possible unit will reduce the initial cost.
2. A furnace that is too large for the home will cycle on an off frequently, making the home less comfortable than an appropriately sized furnace.
3. Temperature swings from cycling may cause the homeowner to turn up the thermostat, which will result in higher energy bills.
4. Incorrect sizing can put stress on the system and shorten equipment life.

The bottom line: Sealing leaky ducts and using load calculations to choose the smallest possible furnace will assure maximum comfort and efficiency for your customers.

A Bird in the Flue is Worth … A Stainless Steel Intake Cover

by Trey Muffet on July 19, 2010
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Simple proactive measures can prevent hours of head-scratching and time wasted trouble-shooting problems that could have been avoided in the first place. But unfortunately, we can’t always predict the scenarios might diminish the performance of installed equipment—or even render it useless, as happened to us on a retrofit job we completed last summer. In this case, we learned the hard way that putting stainless steel mesh covers on intakes is a pretty good idea.

The job in question involved installation of a 95% sealed combustion furnace as part of a performance package. After installation, the furnace was tested for combustion safety and commissioned. A few months later, when outdoor temperatures began to drop, the client turned up the heat. Nothing. The inducer motor was running, but the blower wasn’t kicking on and the furnace wasn’t firing. After much deliberation, we found that the inducer motor wasn’t creating enough pressure, so we replaced the bad inducer motor. After that the furnace worked fine.

Why would a perfectly good inducer motor that worked flawlessly upon installation fail in a matter of months, even though the furnace had been sitting idle the whole time? The answer became clear when further inspection revealed a sparrow’s nest in the intake, which was blocking the flow of air to the motor. And that’s not the only time we’ve seen evidence that intake and exhaust vents can be attractive hiding places for curious critters. A similar situation lead us to find a stash of acorns in an intake (the elusive squirrel was never found).

Now our standard practice is to install mesh covers on all external vents—a quick and affordable fix that can save us and our clients a lot of headaches in the future.

Duct Diagnostics: Locating Leaky Duct Runs Without a Duct Blaster

by Trey Muffet on July 12, 2010
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Here’s something to bear in mind the next time you reach for your duct blaster: At Recurve, we’ve found that using a duct blaster to diagnose leaks isn’t always time well spent. And we all know that in the Home Performance business, time is money.

The problem is that you can spend hours in cramped spaces sealing ducts only to find that there’s little real improvement in leakage levels, and using a duct blaster to locate leaks is a slow process. The alternative? Using a pressure pan in conjunction with a blower door can help you quickly zero in on leaky duct runs that need the most attention, so you can achieve good results in much less time.

Assuming you’re already running a blower door on most of your projects (or have one easily accessible), a pressure pan can take the place of a duct blaster for determining the highest priority areas to seal. With the house prioritized to 50 Pa by the blower door, record the pressure drop with the pressure pan when it covers the register. A large pressure drop (3-6 Pa) indicates that significant leakage is occurring close to that location. A small pressure drop will indicate there is no leakage in that duct run, or that the leakage is far away.

Don’t get us wrong—duct blasters are essential equipment in situations where you need to perform a rigorous leak test. But this quick pressure pan test can save an hour or more compared to taping off the registers and running a duct blaster test, and anything you can do to achieve the desired results in less time will benefit both you and your clients. The bottom line: Knowing where to focus your energy to save your clients’ energy can give you a real competitive advantage.

Turn More Audits into Sales: The Basics of Selling Home Performance

by Trey Muffet on July 9, 2010
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At Recurve, we’ve found that every technician who performs home energy audits is also a sales person. And the first rule of sales is, “When you’re talking, you’re not selling.” In other words, if you’re not a good listener, you won’t truly understand your customer’s needs and concerns.

When I first started at Recurve, I was so excited about building science that I couldn’t contain my enthusiasm. I found myself talking nonstop to customers about some pretty technical stuff—like the complex physics behind duct leakage, or the finer points of buoyancy forces and the stack effect. But over time, I realized that all of my lecturing about building science wasn’t motivating many customers to buy. It became clear to me that most customers buy retrofits to address specific problems they are experiencing with the comfort, energy efficiency or indoor air quality of their homes—not because they’re worried about pressure differentials in their heating ducts.

To accelerate sales, you need to do what I did: Stop talking at your customers and start asking more questions. And bear in mind that not all kinds of questions are equally effective. Asking open-ended questions (questions that can’t be answered with a simple “yes” or “no”) is the best way to gain trust.

Here’s an example of the kind of closed question we avoid asking our customers:

Q: Is your home uncomfortable in the winter? A: Yes

An open question goes more like this:

Q: How would you describe your comfort level during the winter? A: It’s terrible! We’re all bundled up half the time, and the house is very drafty, but we don’t like to run the heater too much because the heat doesn’t seem to stay inside anyway.

Notice that with the open-ended approach, you’ll end up gathering a great deal of information that can be used later to support your recommendations to the homeowner. “We’re going to seal up and insulate your attic. What that’s going to do is cut down on the drafts you told me you feel in the winter, and help your home hold the heat longer. You’ll be more comfortable, and you’ll save on your heating bills.”

The more you can get your customers to open up, the more you’ll learn about their real motivations. We’ve found that the majority of homeowners will tell us at the beginning of the process that they want to achieve X, and end up making a decision to buy because of Y and Z. The key to getting to these “real” motivating factors is to ask open-ended questions that will reveal more about what the customer is experiencing. We have found that linking one open-ended question to next in a natural, conversational tone builds trust—and trust leads to good relationships.

Are you listening yet?

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