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A/C: Bigger is NOT Better

July 15, 2009

Part of the continuing myth-busting series.

Energy Myth:  For Air-conditioning, a larger unit is better.

Reality:  Bigger simply is NOT better.  In fact, too big is much worse than the “right size”, and often worse than a little bit too small would be.

Unfortunately, because it allows them to take short cuts on determining the right size, and not worry about duct leakage or poor insulation, many contractors fudge it, and install a ton or more of extra capacity.   Don’t fall into this trap.  The benefits of a properly sized air conditioner are huge. 

A sad thing is that an oversized A/C costs you on the front end and throughout its life.  A bigger unit costs more.  And thus you lose right out of the gate.

Oversized units “short-cycle”.  That is they turn off quickly.  Air conditioners don’t gain their full efficiency for several minutes after start up.  If you’re A/C shuts off before that, it’s not operating at peak efficiency, and you can pay up to 10-20% more.

But it’s worse than that.  Air-conditioners remove less humidity from the air at the beginning of their cycle.  And longer run times help pull more moisture from the air.  So an oversized unit, which runs less, will leave a house feeling clammy even as the air temperature is dropped.

Bigger capacity also means a bigger fan (assuming the contractor even looked at air-flow).  And all else equal, a high air-flow means more noise—really high air-flow can create downright annoying noise issues.  And the short run times don’t allow the air time to mix—you get blasts of cold air.

In short…

A too-big A/C costs more up front, costs more to run, won’t remove humidity as well, can be noisier, and less comfortable.

A right-sized A/C costs less than an oversized unit, is less expensive to run, does a better job removing humidity, can be quieter, and with longer run times does a better job mixing the air and delivering consistent comfort.

Don’t let your contractor talk you into something bigger than you need!  And ask to see the sizing calculations, generally the “Manual J” sizing.  [Even better, ask how you can tighten ducts, increase insulation, and reduce heat gains, to get an even smaller unit.]

Stay cool,
Mike

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Posted in Air Conditioning, Consumer Protection, Heating & Cooling Tips, Uncategorized | 1 Comment »

Insulate to Stay Cool

June 18, 2009

Let’s talk about staying cool this summer.   I’ll run through a variety of cooling tips later.  Today, though, I want to discuss insulation.   Not that exciting, perhaps, unless some of the itchy stuff get down your shirt!  But important.

Many people think insulation only helps you stay warm in the winter.  It also helps you stay cool in the summer.   Anybody who has ever been in an attic in the summer knows how hot it can get.  140 degrees or even higher.  That might be 70 degrees warmer than you want it!  Well, that heat conducts and radiates down into your home and bakes you.  And simply stated, insulation stops the flow of heat.  So by increasing your attic insulation levels you block that tremendous heat in your attic and you stay cooler in the summer.

Of course, the insulation works in the other direction in the winter, keeping heat in the house—so you save twice.   You stay cooler in the summer, warmer in the winter, and you save energy and spend less on utility bills year round.

As I’ve discussed before, insulation really only works if you air-seal first.  A good contractor will carefully air seal any leaks between the attic and the area below before installing insulation, leaks such as around recessed lights, attic access doors, and exhaust fans.  In fact, the U.S. DOE found that air infiltration can account for 30% or more of a home’s heating and cooling costs and contribute to problems with moisture.  Air sealing saves you money and keeps the cool air inside during the summer—and the warm air inside during the winter.  While the contractor is in the attic, he should make sure that any ductwork up there is sealed and well-insulated.  Increasing attic ventilation can also help, but that can increase winter heating bills if air-sealing isn’t done, too.

Even if you have air-conditioning, be sure to upgrade your attic insulation.  You’ll use the AC less, and if you’re getting a new air-conditioner, you’ll be able to downsize a smaller, less expensive system (with AC, bigger isn’t better!), and you’ll save twice, first on the cost of the smaller unit and then on the cost to run it.

I’ll get into some other cooling tips later.  Meanwhile, insulate and stay cool.  And check out the tax credits available to help make that happen. 

Thanks,
Mike

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Posted in Air Conditioning, Heating & Cooling Tips, Insulation, Uncategorized | 2 Comments »

Is It Time to Replace That Air-Conditioner?

August 4, 2008

With the high temperatures (and soggy humidity in the Northeast), here’s a question we’ve gotten a lot likely.  How do you know when it’s time to replace your air-conditioner?  There are several warning signs.  First, any air-conditioner that is more the 10 years old is a candidate for replacement. Energy efficiencies have improved dramatically, and top contractors like GreenHomes can install this new equipment so that you can get the most out of it.  Age of the equipment alone, though, isn’t the only sign that you may be ready. ENERGY STAR offers some guidelines for homeowners that make a lot of sense.  It’s time to call for help if any of the following apply.

  • Your equipment needs frequent repairs and your energy bills are going up. There are a variety of problems that can creep in over time to make your cooling equipment less efficient.  Although some can be repaired, occasionally replacement can be more cost effective.
  • Some rooms in your home are too hot or too cold.  Improper equipment operation, duct problems or inadequate insulation could be the cause.
  • No one is home for long periods of the day and you do not have a programmable thermostat.  Install an ENERGY STAR qualified programmable thermostat or have a good contractor install one and instruct you on its use — to start saving energy and money while they’re away or sleeping.
  • Your home has humidity problems.  Poor equipment operation, inadequate or oversized equipment, and leaky ductwork can cause the air to be too dry in the winter or too humid in the summer. 
  • Your home has excessive dust.  Leaky ducts can pull particles and air from attics, crawl spaces and basements and distribute them throughout your house. Sealing your ducts may be a solution.
  • Your heating or cooling system is noisy.  You could have an undersized duct system or a problem with the indoor coil of your cooling equipment.  
  • Your score on the U.S. EPA’s Home Energy Yardstick is low.  The Yardstick helps you determine how your energy use compares to others in homes like yours.

If any of these apply to you should have your system evaluated.  Make sure though, that you get a comprehensive assessment of your home first.  Many problems that appear to be with your heating and cooling equipment are actually caused by poor insulation, air leaks, windows, or other issues.  Unfortunately, these problems can be found even in newly constructed homes, and regardless of when it was built your home should get a thorough evaluation.

Much of the above applies to your furnace as well.  New “ECM” furnace motors are much more efficient than standard models and can lead to huge savings your electric bill.  Because inefficient motors actually generate waste heat, equipment with these new motors saves you twice with your air conditioning!  But I’ll talk more about furnaces later.

-Mike 

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Posted in Uncategorized | 1 Comment »

8 Tips on How Not to Lose Your Cool

July 24, 2008

With much of the country sweating through the second heat wave of the summer, and the cost of energy spiraling ever upwards, homeowners are searching for ways to stay within their home cooling budget. Bumping up the thermostat, or opting for fans rather than air conditioning, are two obvious options, but there are some simple things you can do now to achieve significant savings on energy, while still keeping your family comfortable. Here are eight tips from GreenHomes America that will help you keep the bills down, and comfort up, this summer:

1.     Start by keeping cool air in, and hot air out! When the temperature drops at night, if it’s cooler outside than in, open your windows. In the morning, shut them, and keep shades down to block out direct sunlight.

2.     Focus on your attic.  In the summer, temperatures in the attic can climb to more than 150oF.  This tremendous heat can conducts down into your home in a variety of ways.  Insulating and air-sealing your attic will have a huge impact. 

·       Carefully air seal any leaks between the attic and the area below. Common air leak sources include recessed lights, gaps around chimneys, plumbing penetrations, and the attic hatch (which contractors often overlook when insulating the attic).

·       Only after you’ve done air-sealing, put an extra layer of insulation on the attic floor, on top of the insulation you currently have there.  Sixteen to 24-inches is not excessive —and will help keep you warmer in the winter, too!

3.     Use efficient lighting and appliances.  With incandescent and halogen lights, most of the electricity goes to producing heat rather than light.  Not only does this mean you’re overpaying for lighting, but you’re creating a lot of unwanted heat in the rooms you’re trying to keep cool.  Compact florescent light bulbs have improved greatly over the past several years, so there’s no need to worry about the humming, slow starts, and ghoulish colors of years past – and they’re efficient and run cooler. With lighting or appliances, look for Energy Star® qualified models. 

4.     If you have a central or window air-conditioner, keep it tuned up. Clean the filters so they’re not clogged, and vacuum the dust and cobwebs out of the condenser fins.  If it’s more than 10 years old, consider replacing with a high-efficiency unit, one that at least qualifies for Energy Star.

5.     Do you have a forced air heating or cooling system? Seal and insulate the ductwork in attics and crawl spaces.  As much as 30% of the air you cool (or heat in the winter) can escape outside through leaky ducts.

6.     Use a bath fan vented to the outside to remove the heat and humidity created by showering. If you don’t have a bath fan, install one. If you do have a bath fan, make sure it’s powerful enough to do the job (often builders skimp on this). To check, close the window, turn on the fan, and close the door to the bathroom so its open just a crack: standing on the inside, can you feel air moving through the crack? If not, consider upgrading your fan.

7.     Similarly, use a kitchen exhaust fan to remove heat and moisture created by cooking.  This has the added benefit of removing pollutants, especially if you cook with gas.

8.     Planting deciduous trees on the south side of a house can help keep your home cool in the summer.  In many parts of the country, maples, oaks, and birches are good trees to consider.  Because they drop their leaves in the fall, they let sunlight through to help warm your house in the winter.

Many of these tips are simple things you can do to start saving right away.  With some advice from your local home center, and two or three free weekends, a handy homeowner can tackle these projects. The energy savings, and effect on comfort, are cumulative, so do as many as you can. To get even deeper savings, get a comprehensive home energy assessment, and let trained and certified crews install your improvements. 

And whether you do the work yourself or you have it done by a contractor, after you make any changes to the house you should have any combustion equipment like furnaces and water heaters tested to make sure they’re running safely and efficiently.  

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Posted in Uncategorized | 4 Comments »

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