Ducts | Boilers | Distribution
Pipes | Radiators | AFUE
| Types of High Efficiency Heating Systems | Care
of Your Heating System | Using Energy Wisely
| Safety | Common Terms
Your heating system is usually the largest energy-user
in your home, so choosing a new energy-efficient unit is
especially important. When shopping for a new gas heating
system its important to compare efficiencies and
installation costs of various models.
Look for models Design Certified by the American Gas
Association to ensure safety, reliability and efficiency.
Most homes have central heating systems which generate
heat at a central point and distribute it by air, water
or steam to each room in the house. The appliance that
supplies heat to an air transfer system is a
"furnace"; the appliance used to heat water or
furnish steam is a "boiler."
Warm Air Heating Systems (Furnaces)
- Gravity - Heated air rises from the
furnace through large supply ducts. Cool air
returns to the furnace through cold air return
ducts. The weight difference between warm and
cool air keeps the air circulating.
- Forced Air - Warm air is forced through
supply ducts by a blower; it enters a room
through registers or diffusers, then returns via
a cold air duct to the furnace where it is
filtered of dust and dirt particles, reheated and
|Warm air ducts and cold air returns that pass through
cold areas (such as an unheated basement, crawl space,
garage or areas of your home that you do not wish to
heat) should be insulated. Before you insulate ducts, use
mastic tape to repair any holes or cracks in seams.
- Gravity - Operates on the principle that
warm water rises. Hot water circulates from the
boiler through large supply pipes, to the
radiators. Cool water returns to the boiler due
to the weight difference between warm and cool
water. The lowest radiator must be located above
the top of the boiler.
- Forced - Hot water is distributed by a
pump. Pipes that carry the water to the boiler
can be located above or below the boiler.
Hot water heating systems include an expansion tank to
provide a cushion of air for heated water to expand
against so pressure doesnt become excessive in the
Distribution pipes carry hot water from the boiler to
radiators throughout the house, and back to the boiler.
Pipes should be insulated if they pass through unheated
areas such as an unheated basement, crawl space or
Radiators should be full of water for maximum heat
output; air in a radiator obstructs the water flow. 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,
there may be air in the radiator. Keep radiators free of
air by bleeding them when needed and adding water as
required, according to manufacturers instructions.
If manufacturers instructions for bleeding
radiators are not available, open the bleed valve to
allow air to escape; 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 the
The Federal Energy Agency requires all furnaces and
boilers be given operating efficiency ratings -- the
annual fuel utilization efficiency (AFUE). The AFUE tells
how much heat the system extracts from the fuel it burns
during a single heating season. The higher the AFUE, the
more efficient the equipment. The minimum efficiency
standard for new furnaces is 78% AFUE.
A high efficiency furnace or boiler has special
efficiency features which raise the AFUE. These features
may include electronic ignition, power draft system,
improved burner, vent damper, high efficiency heat
exchangers, and secondary heat exchangers in the highest
- Condensing Furnaces In a condensing furnace or
boiler, an enlarged heat exchanger surface lowers the temperature
of the exhaust gases, making the furnace more efficient. The exhaust
gas temperature drops to the dew point of the water vapor in the gas,
causing the vapor to condense to water and give up 970 Btus for every
pound of water condensed. Natural gas can yield more than 1 gallon
(8 lbs) of water per 100,000 Btus (one therm) burned, giving up about
7,760 Btus. Condensing furnaces achieve AFUEs up to 94 percent.
- Heat Transfer Module Boiler/Warm Air System
(HTM) The heat transfer module system uses a
glycol/water solution that is heated and passed
through a blower/coil unit which distributes
heated air throughout your home. It does not
require a conventional chimney, can be located
outside, and can achieve an AFUE of 90 to 95
- Recuperative or Partially Condensing
Furnace/Boiler A recuperative heat exchanger
section is added to the conventional heat
exchanger and the exhaust gases are vented to the
atmosphere by a small fan. A conventional chimney
is not necessary; flue gases can be vented
directly outside. Some units require a vertical
vent; others can be vented through a side wall.
Formerly "lost" heat is captured in the
recuperative heat exchanger section. Some water
vapor in flue gases is condensed, allowing
additional heat to be released for use in your
home. The water is disposed of by a condensate
drain. Loss of heated air when the furnace is not
operating is reduced by restriction through the
forced draft fan. Achieves an AFUE of 81 to 88
- Power Draft Furnaces While a conventional
furnace draws air into the combustion chamber by
natural draft, power draft furnaces use a
motor-driven fan at the burner level to push
(forced draft) or pull (induced draft) air into
the combustion chamber. Some forced draft and
induced draft furnaces allow for a normal chimney
and can be from 80 to 83 percent efficient. (See
Standard Furnace with Vent Damper
Standard design has atmospheric gas burners and a
gravity venting system; an automatic vent damper closes
when the furnace shuts off so less heat escapes up the
- Home heating systems need periodic care. Proper
maintenance will extend the operating life, save
energy and increase efficiency. Follow
manufacturers recommendations in caring for
- Cleaning or adjusting natural gas burners should
be done bya qualified serviceperson. If your
heating system is not working properly, contact a
qualified heating contractor. The following
conditions indicate the heating system could be
operating inefficiently or unsafely:
- odors and/or irritation to your nose or
- 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 unit 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
- Vents and Chimneys - Visually inspect the chimney and the vent connector
(the pipe between the furnace or boiler and the chimney) for rust
holes or corrosion. These conditions may allow hazardous flue products
to enter your home. Replace any defective vent connector or
- Pumps, Blowers, Motors and Filters - Before
working on your heating system, TURN OFF THE
ELECTRIC POWER TO THE FURNACE OR BOILER. Most
pump and fan motors require periodic oiling.
(Some newer motors are permanently lubricated.)
Consult manufacturers instructions on
oiling. If they are unavailable, look for a tube
or hole on both ends of the motor, directly above
the motor shaft. Oil at least twice during the
heating season, using non-detergent #20 oil, two
or three drops per location. Do not
over-lubricate; too much oil will soak into the
motors insulation and shorten its life. The
blower (fan) may also be permanently lubricated.
Look for cups at each end directly above the fan
shaft. Fill oil cups with non-detergent #20 oil
twice during the heating season.
- Blower blades require occasional cleaning; dust
and dirt reduce their air capacity, causing
overheating and fuel waste. To do this, remove
the blower assembly from the furnace and use a
brush, such as an old toothbrush, to clean the
blades. Be careful not to bend the blades or
remove small clips attached to them. These clips
are balance weights installed to ensure
- Check the V-belt that connects the motor and
blower pulley and replace if worn or cracked.
- Check filters monthly and replace or clean when
dirty to prevent damage to blower or fan motor
and maintain efficiency.
- The main gas valve turns the burner on and off.
It is electrically controlled by the room
thermostat, pilot safety device and the maximum
temperature limit control.
- The maximum limit control keeps your heating unit
from overheating. On a furnace it is called a
limit control; on a boiler it is called an
- Registers - Look for and correct the following
- closed supply dampers
- drapes, furniture or carpet obstructing the supply and/or return registers or grilles
- leaks in warm air ducts and cold air
- dust plugging the supply and/or return
registers or grilles
- high pile carpet blocking baseboard
radiators at the bottom
- Lower your thermostat setting at night and when
there will be no one home for at least 4 hours; a
10° setback can give you significant savings.
Setback thermostats save energy by automatically
turning the thermostat down and up on a preset
- If you turn off the pilot during summer to save
energy, you should know how to safely relight it.
It might not be economical to hire a
serviceperson to relight the pilot.
- In recent years, a number of "energy-saving
devices" (retrofit devices) have been
developed for heating systems. The cost
effectiveness of a retrofit device depends
primarily on the age and condition of your
heating system. Generally, older systems have
fewer operating years remaining, so retrofit
devices will be less cost-effective. Before
considering any retrofit device, check with your
local building inspector to see if it complies
with code. It should also be American Gas
Association (A.G.A.) or Underwriters Laboratories
- Keep furnace area clear of flammable liquids
(gasoline, paint products, solvents or cleaners)
and all combustible materials (newspaper,
cardboard boxes or rags).
- The furnace runs longer during very cold weather
to maintain the thermostat setting, so duct and
register surfaces may be hot. Prevent children
from touching or playing near hot surfaces.
- If the pilot goes out, look for relighting
instructions printed on the furnace. If it goes
out repeatedly, call a qualified heating
- All fuel-burning appliances need sufficient air
for proper combustion. If a natural gas, oil,
coal, kerosene or wood heating appliance does not
receive adequate intake air, it will not burn the
fuel completely and may operate inefficiently.
Under certain conditions, carbon monoxide could
be produced and enter the home if the chimney or
vent connector is defective.
- Provide sufficient ventilation to your home when
using a fireplace by opening a nearby window or
adding a fresh air intake to the fireplace.
- Automatic Vent Damper - A device attached in the
venting system after the draft hood. It automatically closes the vent
when the furnace or boiler is off, restricting heated air from going
up the chimney.
- Intermittent Ignition Device (IID)/Electronic Ignition
- Uses a spark or other heat source to ignite the pilot when the thermostat
calls for heat. Replaces a continuously burning pilot flame.
- Heat Exchanger - A section of the furnace or boiler
where heat generated by the combustion process is transferred to circulating
air or water.
- Flue gases - The products of combustion (carbon
dioxide and water vapor) which are vented to the outdoors.
Call your local natural gas utility
company or the Minnesota Blue Flame Gas Association at