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Boilers use oil, natural gas, propane or electricity to heat water which is then distributed throughout the home by means of a water pump.  Once the heated water reaches the living area, hot water heat is circulated through radiators, baseboard convectors, radiant floors, and heating coils in air handling units to provide central heat.


Boilers use oil, natural gas, propane or electricity to heat water which is then distributed throughout the home by means of a water pump. Once the heated water reaches the living area, hot water heat is circulated through radiators, baseboard convectors, radiant floors, and heating coils in air handling units to provide central heat. 

Whether investing in a new boiler or improving the performance of an existing one, reducing the amount of energy you use to heat your home will save you money and conserve natural resources.

Quick Links:
What are my options?
How to buy?
Energy-Saving Tips
How much can I save?

What Are My Options?

Condensing Boilers. These units cool the combustion gases that are normally released into the atmosphere. Water condenses from those combustion byproducts, which releases additional heat and raises the overall efficiency of the system.  Because of this additional cooling and condensing, these models can have AFUE’s up to 98%.

ENERGY STAR qualified boilers have an AFUE rating of 85% or higher. Their features include:

Electric ignition, eliminating the need to have the pilot light burning all the time.
Modern combustion technologies that extract more heat from the same amount of fuel.
Some units have sealed combustion, bringing outside air into the burner rather than using already heated indoor air for combustion. This feature improves the safety and comfort of your home and eliminates the possibility of back drafting through chimneys.

Indirect Water Heater. New boilers that are well insulated and have a low thermal mass can be utilized as efficient water heaters. If you are installing a new boiler, think about replacing your existing storage water heater with a well-insulated indirect tank that connects to the boiler with an external loop.  This combination will save energy because heat losses through the water heater flue will be eliminated.

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How To Buy?

Sizing a Boiler. Boiler systems should be sized to meet the maximum household demand during the normal heating season.  Boilers that are too small will not provide sufficient heat and boilers that are too large will cost more and be less efficient.

A correctly sized boiler will reduce maintenance costs by starting and stopping less often, and reducing the amount of heat lost up the flue during the off cycle.

When you are selecting a contractor, ask that they use a sizing tool like ACCA Manual J to take into account factors including:

Size, shape and orientation of the house.
Local climate.
Insulation levels.
Type of construction.
Window area, location, and type.
Air infiltration rates.
Your family’s particular heating needs.
The most common sizing mistake is buying an oversized unit.  This can result in large – and uncomfortable - temperature swings – higher installation cost, shorter system life and higher energy costs.

Boiler Efficiency. The efficiency of a boiler is indicated by its Annual Fuel Utilization Efficiency (AFUE).  This is the ratio of heat output compared with the total amount of energy consumed. Although this rating does not account for some heat loss in the ducts, new boilers today are typically between 78% AFUE and 98% AFUE.

Below summarizes the general ranges of heating systems in relation to their efficiencies:

Old, low-efficiency gas heating systems:
Natural draft that creates a flow of combustion gases
Continuous pilot light
Heavy heat exchanger
68%–78% AFUE

Mid-efficiency gas heating systems:
Exhaust fan controls the flow of combustion air
Electronic ignition (no pilot light)
Compact in size and weight to reduce cycling losses
Small-diameter flue pipe
80%–87% AFUE

High-efficiency gas heating systems:
Condensing flue gases in a second heat exchanger for extra efficiency
Sealed combustion
90%–98% AFUE

Besides using less energy, investing in an efficient boiler will improve the comfort and air quality of your home.  Efficient boilers cycle on and off less often and have more advanced controls to provide the desired temperatures throughout your home. Some boilers operate as sealed combustion units that draw air for combustion from the outdoors rather than from inside your home.

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Energy-Saving Tips

Retrofitting a Boiler. By adding certain devices to your existing system, you can increase the efficiency and save money on your energy bill.

Addition of a vent or flue damper:
Prevents chimney losses.
Closes off the vent when the boiler is not firing.

Intermittent ignition devices:
Applies to older gas systems that are equipped with a continuous pilot light
Are difficult to install – hire a professional to do this.
Cost about $250 and typically have a payback period of less than 10 years.
Save money in fuel costs, but are not always cost effective for aging equipment.

Derating Gas Burners:
This applies to oversized systems in many homes.
Reduces the heating capacity of your gas boiler to make it operate more efficiently.
Reduces the size of the gas burner orifice, and possibly also the baffles.
Should only be done by a qualified technician.
Should cost less than $100 and can save up to 15% of your fuel costs.

Modulating Aquastats:
An aquastat monitors the temperature of the water in the boiler, but a modulating aquastat, or “outdoor reset” control senses outdoor conditions and changes the hot water temperature in the boiler in relation to outdoor temperature.   The units cost several hundred dollars, and can save up to 10% of fuel costs.

Time-Delay Relay:
A time delay relay is a way to squeeze more heat out of your system. When the thermostat clicks on, the relay causes the boiler to circulate residual hot water through the system without firing the boiler. The boiler will fire up only after a set time.

A time delay relay costs about $100, but can cut your fuel costs by up to 10% and makes use of all of the energy you pay for.  If you are retrofitting your existing system, have the technician perform a combustion-efficiency test, and adjust the burner for peak efficiency.

Conservation and Efficiency Tips. The easiest way to lower your energy bill is to conserve the generation of heat.

Thermostats. At night, turn down the thermostat when you are away from home.  You can save about 1% of your heating bill for every degree that you lower the thermostat for at least 8 hours each day. Turning down the thermostat from 70°F to 60°F overnight saves about 10% ($100 saved per $1,000 of heating cost).

Programmable Digital Thermostats. Allow you to adjust the times you turn on your furnace according to a pre-set schedule. This way, the unit does not operate as much when you are asleep or when the house is not occupied.

Manually Adjusting Your Aquastat. The aquastat controls the temperature of the water in a boiler, which is typically kept at 160-180°F.  During warmer seasons, water that hot is not needed to heat your home, and therefore it is a waste of energy to maintain this temperature.

An easy way to conserve energy and save money is to manually change the setting of the aquastat. The aquastat control is usually located in a metal box connected to the boiler.  In warmer seasons, this device should be set manually to 140ºF (120ºF with condensing boilers), reducing fuel consumption by 5-10%.

Control Options. Some boilers are available with integrated controls that include the outdoor temperature reset controls described above to reduce the amount of heat lost during off-cycle periods or on warmer days.   Other types of controls that help reduce losses can be retrofitted to existing boilers

Typically, the controls that reduce off-cycle losses function best with condensing boilers.  But any boiler can benefit by being wired for “cold” starts, where no heat is maintained in the boiler unless there is a need for heat in the house. Ask an installer or technician about these options.

Zone Control. To get the most use out of the energy you pay for, controlling the heat distribution is key. You can retrofit your system and create different “heating zones” within your home.  Zone control is generally most effective for specific rooms or areas of the house that are not used frequently or are used at different times from other parts of the home.

A professional can install automatic valves on the hot-water radiators, which are controlled by thermostats in the separate zones of the house. Programmable thermostats will also allow you to heat specific parts of your home on a schedule you select.

Where Zone Controls Works Best. Some homes, of course, are specifically designed to utilize this feature. It will not work well in homes with no distinct room separations. When the colder sections of the home can be isolated from the others by doors or walls, zone control works best.  Cooler parts of the home should be kept at least 50°F in order to keep water pipes from freezing.  Remember to never shut off the heat entirely in an unused part of your home.

Maintenance Tips. When properly maintained, your heating system will not only perform better, but also last longer.

Observe the state of the vent connection pipe and chimney.   Parts of the venting system may have deteriorated over time. Chimney problems can be expensive to repair; instead you may consider purchasing a new heating system that does not need a chimney.

Check the condition of the heat exchanger. If you suspect a leak, have the boiler examined by a trained professional.

Water temperature settings. Adjust the controls on your boiler to provide the most appropriate water temperature settings for both efficiency and comfort. Test the relief valve and high-limit control.

Trapped Air. Bleed trapped air from hot water radiators and follow prescribed maintenance for steam heat systems, such as maintaining water level, removing sediment, and making sure air vents are working. Check with your heating system technician for specifics on these measures and use caution: Steam boilers produce high-temperature steam under pressure.

Tune up the heating system. Oil-fired systems should be tuned up and cleaned every year, gas-fired systems every two years, and heat pumps every two or three years.  Regular tune-ups not only cut heating costs, they increase the lifetime of the system, reduce breakdowns and repair costs, and cut the amount of carbon monoxide, smoke, and other pollutants pumped into the atmosphere.  Inspect the pressure tank to make sure it is filled with air and not water.  Clean the heat exchanger.

Benefits to You and Your Community. Boilers use fossil fuels to heat your home, and emit exhaust gases out the stack into your neighborhood.  By maintaining combustion efficiency, conserving energy with a programmable thermostat and boiler controls, and purchasing a high efficiency boiler, you will save money, reduce your energy use, reduce the need for utility capacity increases and improve the air quality in your neighborhood and world.

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How much can I save?

Boiler Operation and Maintenance Costs. Select a system based on the operation and maintenance costs of the complete system and not just the initial cost of a boiler.  The evaluation should consider costs for venting, makeup air, pumping arrangements, and controls.  The more efficient models cost more to purchase, but will save you money in energy costs in the long-term.

Replacing an existing boiler is about $2,500 -$4,000 for a mid-efficiency system and $5,000 -$9,000 or more for a high-efficiency version.
If you are replacing an old boiler with a more efficient model, installing a chimney liner may be needed. This can cost about $300 -$700 for a gas model and $700 -$1,800 for a fuel oil appliance.

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Keystone Energy Efficiency Alliance
1501 Cherry St.
Philadelphia, PA 19102

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