Gravity system
A gravity system operates on the principle that warm water or steam rises. Hot water or steam circulates from the boiler through supply pipes to the home's radiators. Cooled water returns to the boiler due to the weight difference between warm and cool water. The lowest radiator must be above the top of the boiler.

Forced or pumped system
Hot water is distributed via a supply pipe powered by a pump. Cooled water returns to the boiler via a return pipe. Radiators can be above or below the boiler.

In either system, the radiator is generally built into the floor (typically found in new construction), a tube and fin system of baseboard radiators, or in older homes, cast iron radiators are commonly found.

High-efficiency systems
There are now very high-efficiency boilers available that have AFUE ratings of over 95 percent, some hang on the wall, taking up no floor-space at all. Click here for rebate information

Hot water for your shower, too
Boilers are often combined with a water storage tank, called an indirect or side-arm system, to efficiently provide abundant hot water for showers, tubs, dishwashing and more.

• Be sure nothing is obstructing the air flow around your radiators. Drapes, furniture, layers of paint and high-pile carpet can all reduce a radiator's performance.
• Inspect the "cold-end' of the flue for ice build-up that could restrict the exhaust.
• Ensure that the fresh-air intake is free of debris, snow, ice, etc.
• Distribution pipes carry hot water from the boiler to radiators throughout the house, and back to the boiler. Supply pipes should be insulated up to the radiator. Supply and return pipes should be insulated if they pass through unheated areas.
• Radiators should be full of water for maximum heat output; air in a radiator obstructs the heat transfer. If the radiator is warm at the bottom and cool at the top, or warm at the inlet side and cool at the outlet side, or "hammers", there may be air in the radiator. Keep radiators free of air by bleeding them and adding water when needed, according to manufacturer's instructions. If manufacturer's instructions for bleeding radiators are not available, here are general instructions: Open the bleed valve to allow air to escape - this requires a "key", available at most hardware stores. Close the valve when water begins to flow from it. Start with the radiator located at the highest level in the house and repeat on all the radiators, ending with the one at the lowest level. You may need to add water to the system after bleeding. If you are not comfortable doing this maintenance, hire a qualified professional. See illustration below.

• Odors and/or irritation to your nose or eyes.
• If you smell gas, leave the area immediately. Do not use your phone, electric switches, your computer, or anything that could cause a spark. Go directly to a safe location, and then call CenterPoint Energy and 911.
• 24-hour gas leak hotline
  Minneapolis/St. Paul Area: 612-372-5050
  Toll-free: 800-296-9815

• Soot and carbon deposits on the burner, in the combustion chamber, on the floor near the furnace/boiler or below the draft hood opening buildup of dust, dirt or scale on burners and/or burner components
• A yellow flame rather than a blue flame
• Flame backing up and burning outside the combustion chamber
• Excessive humidity or frost on windows or walls

• Any repairs or adjustments to the valves, burners, pilot safety and limit controls should only be done by a qualified professional.
• If the pilot goes out, look for relighting instructions printed on the furnace. If it goes out repeatedly or you are not comfortable relighting the pilot, call a qualified heating contractor.
• A professional service technician should replace chimney and vent connectors (the pipe between the furnace and the chimney) if there are rust holes or corrosion.

Gas verse electric - operating cost and environmental impact

Choosing a dealer

Get two or three estimates

Replace your water heater and heating system at the same time

• Programmable thermostats save energy by automatically turning the thermostat down and up on a schedule you can easily program.
• In recent years, a number of "energy saving" retro-fit devices have been developed for home heating systems. The cost effectiveness or value of a retrofit device may or may not be worth the investment. Generally, older systems have fewer operating years remaining, so retrofit devices will be less cost-effective. With a newer system, an energy saving retro-fit device may be counter-productive, and may void the warranty. Be an informed buyer. Before considering any retrofit device, check with your local building inspector to see if it complies with code. It should be approved by CSA America or Underwriters Laboratories.

• Check the chimney and vent connector (the pipe between the boiler and the chimney). A professional service technician should replace them if there are rust holes or corrosion.
• Inspect the "cold-end' of the flue for ice build-up that could restrict exhaust.
• Ensure that the fresh-air intake is free of debris, snow, ice, etc.
• Have your boiler checked by a professional licensed service technician once a year to be sure it is performing properly and that it has sufficient air for proper combustion and to exhaust flue products.