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.

The Great Escape

by Shana Fong on July 19, 2010
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The gaps you can find around the windows and doors of the average American house add up to the equivalent of a hole in the wall that measures 10 inches by 10 inches.

Your house has more leaks than the CIA. There are cracks all over the place. Your doors and windows don’t quite meet their frames; there are tiny spaces where the walls almost join the floor; there are open areas around your electrical and plumbing outlets. And these little gaps eat energy. In fact, an amazing amount of heat in the winter – or cool air in the summer – escapes through them. But you have two simple weapons to fight with: caulking and weatherstripping.

Energy Facts

  • Caulking and weatherstripping an electrically heated home can keep some 1,000 pounds of CO2 out of the air. So if 1,000 of these homes were weatherized, over a million pounds of CO2 would be saved.
  • Believe it or not, stopping air infiltration can reduce your home’s heating and cooling bills by up to 40%.
  • People are concerned that although weatherstripping may save energy, it will keep fresh air out of their homes. While it’s true that some ventilation is necessary, it’s really not much of a problem – a typical house may get twice as much fresh air as it needs. In other words, the air is probably flying out of your house as quickly as you’re heating or cooling it.

Caulking vs. Weatherstripping

  • Cracks without any moving parts – like the places where a wall in your house meets the outside edge of a window frame, or two other dissimilar materials come together – can be sealed with caulk.
  • The places where doors and windows close into their frames can be sealed with weatherstripping – cleverly designed strips of felt, rubber, metal, or plastic that fill the spaces around doors and windows, and compress when you shut them.
  • Weatherstripping materials come in many styles. Some are self-sticking, so you don’t even need a hammer to install them. Others must be nailed on. Still others are crafted so pieces on the frame and the door lock together when the door closes.
  • One of the trickiest places to weatherstrip is where the door meets the threshold. Special “shoes” and “sweeps” are available to stop these air leaks.
  • Besides saving energy, weatherstripping and caulking have an additional benefit: By stopping drafts, they’ll make your home more comfortable.

Leak Patrol

  • Some evening, when your house is at least 20°F warmer than the outdoors, hold your hand up to various places around windows and door frames. If you feel any drafts, the windows and door frames need weatherstripping.
  • You can also use a smoking incense stick to look for drafts. Hold the stick near places you think might have cracks; if the smoke dances or gets sucked in, you’ve found a place to seal.
  • Many of the biggest air sealing opportunities are up in the attic and below your floors. For these harder-to-reach leaks, it’s a good idea to call in a trained professional such as Recurve to quickly identify and remedy your home’s major leakage areas.

Excerpted from 30 Simple Energy Things You Can Do To Save The Earth, by The EarthWorks Group.

Dialing for Dollars

by Shana Fong on July 16, 2010
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Is your thermostat accurate? If not, chances are that the temperature sensor is being affected by cold air coming through the opening where the thermostat is mounted.

Keeping control of your thermostat is one of the simplest ways you can save a great deal of energy – and money – all year round.

Energy Facts

  • During the winter, you can save as much as 2%-3% of the energy your furnace uses simply by lowering your thermostat 1°F (if it’s set between 65°F and 72°F).
  • In the summer, the process is reversed. You save 3%-5% of the energy used by your air conditioner for every degree you raise the thermostat setting (if it’s set between 70°F and 82°F).
  • Do you chronically forget to turn down the heat? There are low-priced, easy-to-install thermostats that adjust the temperature automatically. The simplest have built-in clocks; the more advanced models are computerized. An advanced model will, for example, turn your furnace on 30 minutes before you wake up, turn it off when you leave for work, turn it on just before you return home, and then set it for 55°F when you go to bed. Some also have a “minimum energy use” setting that monitors temperatures when you go on vacation.

Simple Ways to Save Energy

  • Keep the thermostat under control. Recommended winter settings for heaters: 68°F in the daytime, 55°F at night. In the summer, turn the air conditioner’s thermostat to 78°F.
  • Check the temperature. Using an accurate thermometer, make sure that the temperature near your thermostat is representative of the rest of the house. If it’s located in a drafty or sunny spot, you may be getting false readings and wasting energy.
  • Plug the hole in the wall behind the thermostat with a piece of fiberglass insulation.

Excerpted from 30 Simple Energy Things You Can Do To Save The Earth, by The EarthWorks Group.

Helpful Seasonal Home Maintenance Calendar

by Shana Fong on January 20, 2010
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Here’s a helpful checklist of things to do around the house, according to season:

JANUARY/FEBRUARY

  • Clean or replace furnace filter
  • Check/clean heat recovery ventilator; wash or replace filter
  • Clean humidifier
  • Clean range hood filter
  • Check basement floor drain

MARCH/APRIL

  • Clean or replace furnace filter
  • Check/clean heat recovery ventilator; wash or replace filter
  • Clean humidifier
  • Check sump pump
  • Check gutters and downspouts and clean if needed
  • Inspect air conditioning; service as needed (usually every two or three years)
  • Inspect basement or crawl space for signs of seepage/leakage
  • Ensure that ground slopes away from foundation wall

MAY/JUNE

  • Clean windows, screens and hardware; install screens
  • Check that air intake and exhausts are clear of debris, nests, etc.
  • Clean range hood filter
  • Undertake spring landscape maintenance; fertilize young trees

JULY/AUGUST

  • Air out damp basements on dry days or use dehumidifier
  • For central air conditioning, clean filter in air handling unit
  • Check exterior finishes
  • Check exterior wood for deterioration
  • Check caulking and weatherstripping, including around entry door from garage and house
  • Check basement floor drain trap; replenish if needed
  • Have furnace/heating system serviced (every two years for an electric furnace)

SEPTEMBER/OCTOBER

  • Check fireplace and chimney; service or clean if needed
  • Clean range hood filter
  • Clean leaves out of eavestroughs
  • Check roofing and flashing for signs of wear or damage
  • Close windows, skylights
  • Winterize landscaping

NOVEMBER/DECEMBER

  • Clean or replace furnace filter
  • Check or clean heat recovery ventilator; wash or replace filter
  • Clean humidifier
  • Check exhaust fans