Feb 9, 2015 3:06:25 PM
Jan 26, 2015 12:52:41 PM
AT THE HEART of most home heating systems is a furnace, a boiler or a heat pump. A furnace burns fossil fuel to heat air that’s forced by a blower fan through a series of ducts to the living spaces; a boiler heats water that’s then pumped to a hydronic, or water-based, distribution system. Most heat pumps run on electricity. They don’t create heat, but rather extract it from the air or the ground. Heat pumps are available for use with forced-air and hydronic distribution systems. If you want to minimize your fuel bill, an Energy Star rating is a minimum standard for these appliances.
A modulating gas furnace is the most technologically advanced fossil fuel-burning furnace you can get, with efficiencies as high as 97percent (that’s the percentage of the fuel’s potential energy delivered as heat). It achieves this feat with a series of technical innovations. Gas is not as clean as we once believed, however, now that dirty methods of “fracking” are used in some extraction. The pollution may simply be happening at the front end of the process. No fossil fuel gets an environmental free ride. It’s a finite resource, not a renewable one.
One way that new technology squeezes more heating power from gas is with an exhaust heat exchanger. This exchanger steals back heat from the furnace’s waste byproducts. Another feature, flame modulation, adjusts the flame size, based on demand. These furnaces include variable-speed blower fans with high-efficiency electric motors. The ability to vary airflow and flame intensity also allows for nearly constant room temperatures and better air circulation.
A boiler burns oil, natural gas or propane to heat water. That heated water is then pumped through a system of pipes to radiators, baseboard heaters or a radiant floor.
A good boiler will offer efficiencies of 90 to 95 percent and will include many of the same technologies as a high-efficiency furnace. These include a modulating burner that matches the heat output to whatever the thermostat is calling for at the moment, advanced heat exchangers to extract more heat from the same amount of fuel, and the ability to recover heat from the exhaust gas by condensing it. The resulting exhaust is cool enough to be vented out of a plastic pipe. In the best cases, this condensing process can squeeze 10 to 12 percent more usable energy out of the fuel.
Air-Source Heat Pump
A heat pump is basically an air conditioner that works in reverse to provide heat. The heat pump captures and concentrates heat from one area, then releases it to another.
In heating mode the heat pump takes heat from the outdoor air and delivers it to the home’s distribution system. In cooling mode, it reverses direction to work like an air conditioner, extracting heat from inside the house and blowing it outside. In cooling mode, this waste heat can also be used for water heating. The most common type is the split system, which uses separate indoor and outdoor units, but you can also get packaged systems that place everything in a self-contained outdoor unit. While air-source heat pumps can offer efficiencies of 200 to 300 percent, they’re most efficient in the southern part of the country. A backup electric or gas heater may be needed when the outside air drops below a certain temperature. Although different versions are made for forced-air and hydronic distribution, the forced-air type is the most common. Heat pumps don’t get air as hot as a furnace or boiler, so may require more airflow to maintain the same temperature.
A geothermal heat pump (GHP) uses refrigerant-filled underground piping loops, installed horizontally or vertically, to exchange heat with the earth. These systems work well in both warm and cold climates. A good GHP is able to move three to five times more energy than it consumes. Models are available for use with forced-air or hydronic distribution systems. While the hydronic models don’t get water as hot as a conventional boiler (122 °F, compared to 150 °F or more) their low temperature output is a perfect match for radiant floor heat.
Jan 26, 2015 11:44:26 AM
SIDING CHOICES ABOUND FOR TODAY'S HOMES. Aesthetics are important when choosing one option over another, and when you take the environment into account, some choices just look a whole lot better than others. According to research from the Freedonia Group, fiber cement, stucco and brick siding will see rapid advances through 2014. Vinyl siding will remain the largest segment. Although long lasting, it’s a controversial material made with polyvinyl chloride (PVC), a plastic that until recently has had a poor recycling record. At least one company (CertainTeed) has now begun to recycle vinyl, and the industry is beginning to look more closely at vinyl’s life-cycle impacts. We haven’t included it here as a “green” option, but we will continue to monitor the industry’s efforts to move in that direction.
Jan 21, 2015 2:33:40 PM
Know the Lingo
R-Value: A measure of how effectively a material resists heat flow. Thus, higher numbers are better.
Batt: A length of insulation that is precut to fit certain wall cavity dimensions. Typically sold in a pre-cut roll.
Unfaced/Faced Insulation: Faced insulation (typically a fiberglass batt) includes a vapor retarder on the interior face that restricts movement of moist air into wall cavities. Unfaced is simply a batt without a vapor retarder.
Ridge Vent: An opening covered by a rainproof vent that follows the peak of the roof, typically required by code. Some insulating methods, however, negate the need for a ridge vent. Clear it with your local code official first.
Blow-In: Method of introducing loose fiberglass, cellulose or mineral wool to framing cavities or attic space, typically using a machine with an attached hose.
Blower Door: Equipment used to test the effectiveness of a home’s insulation and air sealing systems.
Stud Cavity: The space between the vertical members of a conventionally framed wood or lightweight steel home. Common stud spacings include 16” and 24” on center (of stud).
IF YOU'VE EVER opened up the wall of a home built before about 1950, you’ve probably been shocked to find little or no insulation—or at best some crumpled newspapers. And even the earliest serious attempts at insulation with fiberglass look quaint now. Cavities were often only partially filled. Water from outside often leaked in around windows and doors and damaged the insulation. Of course, homes were so leaky prior to the 1960s that walls dried out quickly, so mold wasn’t a big problem.
Jan 21, 2015 10:47:13 AM
This chart shows the approximate R-value per inch of various insulation products. Note, however, that not all product brands have exactly the same performance. More importantly, however, many methods of insulating lean heavily on what goes into the rest of the wall system to achieve good results. For example, blown-in fiberglass or cellulose can provide great results at a very reasonable cost, as long as plumbing and other penetrations are properly sealed, windows are caulked and sealed, and overall air infiltration is minimized with building wrap or (in the case of some types of rigid foam) carefully taped seams.