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Installation considerations: If you choose to replace your heating system, your research will help you in choosing and negotiating with heating contractors. Don't assume that most heating contractors are the same or that most will do a good job. You may get a variety of bid prices and specifications. And the bids may or may not include some very important tasks. Ask the contractors bidding on your heating system to include the following tasks:

  • Calculate the heat load of your home, and size the heating system correctly. Newly installed heating systems are often twice or more the required size.

  • Repair or replace existing chimneys as needed. Many existing chimneys are too large for a modern energy efficient furnace or boiler that is sized to fit the smaller needs of a more energy efficient home. Many older chimneys are unlined or the liner is deteriorated.

  • Seal existing ductwork, if necessary, during furnace replacement. Existing ducts are often leaky, and this leakage is an energy problem if the ducts are located in crawl spaces, attics, or attached garages. All duct joints, located in these unheated areas, should be sealed with duct mastic-a sticky substance superior to tape. Duct tape often fails, and loose duct tape should be replaced by mastic.

  • Install supply-duct insulation in crawl spaces, attics, or attached garages during furnace retrofits.

  • Install supply-pipe insulation in crawl spaces, attics, or attached garages during boiler retrofits.

Consider upgrading boiler supply piping strategies. There are many modern ways to run piping for a boiler that offer advantages to older piping systems. For example, a new piping system could divide the system into zones, each controlled by its own thermostat. Or zones could deliver different water temperatures, depending on the type of heat emitters used (radiators, fan coils, radiant floors). Ensure proper installation by checking that the above tasks are completed before issuing final payment.

If you select the lowest bidding contractor without researching your options, you could get a poor installation that might not provide the energy savings and comfort improvement you were expecting. New heating-system installations are often underbid by 10 to 30 percent, compared to high quality installations. Choose the best contractor based on quality of installation and reputation. And always check references. Don't forget to establish a maintenance schedule for the new furnace or boiler, and stick to it.

Indoor Air Quality: Any time you maintain, retrofit, or replace a gas heating system you also need to be concerned with air quality. Combustion air is needed by all gas heating systems to support the combustion process. This air is provided in some homes by unintentional air leaks, or by air ducts that connect to the outdoors. The combustion process creates several byproducts that are potentially hazardous to human health and can cause deterioration in your home. You can protect yourself from these hazards, as well as maintain energy efficiency, by ensuring that your chimney system functions properly and that your gas heating system is properly ventilated. In some cases, installing a sealed-combustion furnace or boiler can help too.

Chimneys: Properly functioning chimney systems will carry combustion byproducts out of the home. Therefore, chimney problems put you at risk of having these byproducts, such as carbon monoxide, spill into your home. Most older gas furnaces and boilers have naturally drafting chimneys. The combustion gases exit the home through the chimney using only their buoyancy combined with the chimney's height. Naturally drafting chimneys often have problems exhausting the combustion gases because of chimney blockage, wind or pressures inside the home that overcome the buoyancy of the gases.

Atmospheric, open-combustion furnaces and boilers, as well as fan-assisted furnaces and boilers, should be vented into masonry chimneys, metal double-wall chimneys, or another type of manufactured chimney. Masonry chimneys should have a fireclay, masonry liner or a retrofitted metal flue liner.

Many older chimneys have deteriorated liners or no liners at all and must be relined during furnace or boiler replacement. A chimney should be relined when any of the following changes are made to the combustion heating system:

When you replace an older furnace or boiler with a newer one that has an AFUE of 80 percent or more. These mid-efficiency appliances have a greater risk of depositing acidic condensation droplets in chimneys, and the chimneys must be prepared to handle this corrosive threat. The new chimney liner should be sized to accommodate both the new heating appliance and the combustion water heater by the installer.

When you replace an older furnace or boiler with a new 90+ AFUE appliance or a heat pump. In this case, the heating appliance will no longer vent into the old chimney, and the combustion water heater will now vent through an oversized chimney. This oversized chimney can lead to condensation and inadequate draft. The new chimney liner should be sized for the water heater alone, or the water heater in some cases can be vented directly through the wall.

Ventilation: Some fan-assisted, noncondensing furnaces and boilers, installed between 1987 and 1993, may be vented horizontally through high-temperature plastic vent pipe (not PVC pipe, which is safely used in condensing furnaces). This type of venting has been recalled and should be replaced by stainless steel vent pipe. If horizontal venting was used, an additional draft-inducing fan may be needed near the vent outlet to create adequate draft. Floor furnaces may have special venting problems because their vent connector exits the furnace close to the floor and may travel 10 to 30 feet before reaching a chimney. Check to see if this type of venting or the floor furnace itself needs replacement. If you smell gases, you have a venting problem that could affect your health. Contact your local utility or heating contractor to have this venting problem repaired immediately.

Sealed-combustion appliances: Some older gas heating systems rely exclusively upon room air and air leaks for combustion air, while some modern sealed-combustion heating systems have dedicated outdoor air supplies directly to the burner. Sealed combustion furnaces, boilers, and water heaters draw combustion air from outdoors and vent combustion byproducts to the outdoors. Sealed combustion appliances aren't affected by house pressures and are safer than the more common open-combustion appliances, which include most 80+ AFUE furnaces and boilers.

Homes, even new ones, vary in their air tightness quite a bit-some are very tight and some are very leaky. When a home is very airtight, the combustion appliances may malfunction due to a lack of air. The most common malfunctions are combustion-gas spillage and carbon monoxide formation. For this reason, sealed-combustion appliances are the best option for homes that are airtight or depressurized by an exhaust ventilation system. However, any newer furnace should have an induced draft fan that forces flue gases into the vent, unlike older furnaces that have draft diverters, which can allow spillage of flue gases into the home when back draft conditions are present.

  • Summary: Simple Steps to Reduce Heating Costs:

  • Weatherize your home. Insulation and air-sealing improvements to the shell of your home will always improve your comfort, regardless of the size and type of heating system installed. Weatherization may also allow the installation of a smaller, more economical heating system.

  • Use a programmable thermostat. This simple, inexpensive device may provide better savings than any other efficiency measure.

  • Maintain your system periodically to yield immediate energy savings, improved comfort, and a longer trouble-free service for any system. This includes duct repair and replacement.

  • Hire a professional technician to service your heating equipment. Qualified technicians can often identify safety and efficiency issues that aren't immediately apparent. A professional can also teach you about the operation of your heating system and the role you can play in performing minor service tasks.

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