Your Place | Use of programmable thermostats, heat pumps

Posted: October 26, 2007

Question: Our daughter has a heat pump and air-conditioning unit in her house. She has been given two different comments regarding installing a programmable thermostat. One service person has told her she cannot use a programmable thermostat with a heat pump. Yesterday, the serviceman told her she could.

What is the correct answer: Can a programmable thermostat be used with a heat pump/air conditioner combination?

Answer: Good question. According to the Department of Energy, programmable thermostats are generally not recommended for heat pumps. In its cooling mode, a heat pump operates like an air conditioner, so turning up the thermostat (either manually or with a programmable thermostat) will save energy and money. But when a heat pump is in its heating mode, setting back its thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice.

Recently, however, some companies have begun selling specially designed programmable thermostats for heat pumps, which make setting back the thermostat cost-effective. These thermostats typically use special algorithms to minimize the use of backup electric-resistance heat systems. They are probably very expensive, and if they've just come out, they probably aren't ready for prime time.

So I'd accept no as the answer for the present, and have your daughter keep her eye open to any change a year or so down the road.

Q: I'm thinking of pricing a metal farmhouse-type roof for my home. Can you tell me if noise from rain is a real concern, and whether the roof adds more heat to an attic than a traditional shingle roof?

A: First, you'll find that modern metal roofing is much more expensive than many other types of roofs, especially asphalt shingles. I've seen prices of $150 to $600 a square foot installed, which is several times that of fiberglass asphalt shingles.

On the other hand, if you are planning to live in the house for many years, it is highly unlikely your roof will ever need replacing.

Unlike the old metal roofs, new ones are made to last. They are fire-resistant, and, properly installed, they should keep out the elements and resist mildew, rot and bugs. Some come with warranties as long as 50 years. They also are lightweight and installed easily - although metal-shingle installation can be labor-intensive and, therefore, more expensive.

Metal reflects the sun's radiant heat, so the heat at midday is reduced. Still, a metal roof is not an insulator. Instead, a dead-air space is installed between the metal and the decking to make the roof more energy-efficient. Proper insulation and ventilation in your attic will increase efficiency, too.

Is a metal roof noisier than one made of other materials? There's no question that the sound of rain on a metal roof is amplified, and if your bedroom is on the top floor and you're a light sleeper, you'll be awakened by a heavy rain in the middle of the night. Hail or sleet bouncing off a metal roof will be cacophonous, to say the least.

But if the roof deck is solid plywood and if you install sound-deadening insulation beneath the decking, the noise can be effectively reduced.

Remember that golfball-sized hail and heavy objects can dent metal roofs, so check your warranty and homeowner's insurance before too long.


Have questions for Alan J. Heavens? E-mail him at aheavens@phillynews.com or write him at The Inquirer, Box 8263, Philadelphia 19101.

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