While furnaces heat and distribute air,  boilers
heat and distribute water. One of the advantages of an oil-fired
boiler is that it can heat a home’s domestic hot water as well as
heat the home. A separate water heating unit is not needed. Another
advantage of a boiler is that it heats a home very evenly. What’s
more, because of new technology, such as small, flexible air ducts,
homeowners with boilers can now install a central air conditioning
system more easily than in the past.
Additionally, boilers can be used in homes that have duct systems
by means of a hydro-air system. In a hydro-air system, heated water
is sent to an air handler to warm the house. The concept is much
like that of a central cooling system where refrigerant is sent
to an air handler to cool the house. The hot water in the hydro-air
system warms the air in the air handler and the heated air blows
through the ducts to warm the home.
Hot Water Boilers
In a hot water (hydronic) boiler system, heated water from the boiler
is pumped by circulator through radiators, radiant tubing or baseboards.
With hot water heating, dividing the system into separate heating
areas of the home is easily accomplished. Zoning provides efficient,
comfortable, inexpensive heating. Radiant heating, one of the oldest
forms of hot water heating, has made a comeback in recent years
due to its warmth and efficiency. Advances in technology have made
radiant piping more durable and affordable.
Hydronic boiler systems can distribute hot
water through:
* Radiators
* Baseboards
* Convectors
* Vents (hydro-air systems)
Steam Boilers
In a steam system, water heated in the boiler turns to steam, and
the steam moves through radiators to heat the home.
While there are many similarities
between a steam boiler and a hot water boiler, there are a few differences,
including devices found in a steam boiler system that may be unfamiliar.
A Steam Boiler includes:
* Steam valves: Located on the radiators, these valves vent the
air in the pipes to make room for the steam. If you notice white
calcium buildup around a steam valve, it means steam is escaping.
* Gauge glass: This shows the water level in the boiler. The normal
level is usually in the center of the glass. The water level in
the glass will fluctuate slightly when the burner runs.
* Low-water cutoff: Required by code, this device shuts off the
burner if the water level in the boiler falls too low.
* Automatic water feeder: This optional device, which is sometimes
found on steam systems, automatically adds water to the boiler if
the level gets too low. Even if a system has an automatic water
feed, the homeowner should still check the boiler’s water level
on a regular basis.
* Pressure relief valve. The pressure relief valve is a safety device
to prevent the system from over-pressurizing.
* Steam limit control: Sometimes called a pressuretrol, the steam
limit control turns off the burner when sufficient steam pressure
is achieved.
The Condensing Boiler
One of the newer technologies in Oilheat is the condensing, oil-fired
warm air boiler, which features two heat exchangers. Efficiency
ratings of 92% have been achieved, so operating costs can be much
lower. The ultra-high efficiency of the condensing boiler is achieved
by lowering the stack temperature to the point where the steam in
the flue gases turns back into water.
Boiler Designs
Some older oil boilers you may see have been converted from coal.
Due to antiquated designs, these systems are plagued by high draft
loss and poor heat transfer. Newer oil-fired boilers are more efficient,
in part because of low-mass construction and reduced water storage.
This results in less heat loss.
The most common design for steel boilers uses fire tubes. Combustion
gases flow into these long tubes, which are surrounded by water.
The oil burner fires into the combustion chamber, which has a dry
base design.
A dry base design means there is no water surrounding the firebox.
All the water is contained in the upper section of the boiler. Other
steel boilers have a wet base design in which water surrounds the
combustion chamber. This design is more efficient because the hot
gases pass through the fire tubes twice before they are vented.
The wet base design is also called a two-pass system. Like steel
boilers, cast-iron boilers also have dry base and wet base designs.
In a cast-iron boiler, the hot gases rising out of the firebox pass
over the outside of each of the boiler’s cast sections through flue
channels which are located between the cast sections. The gases
are then vented through the flue pipe to the chimney.
All boilers have internal passages for the combustion gases. If
the passages are too wide, the heat transfer rate will be low. Combustion
gas passages that are too wide are often a problem in boilers converted
from coal to oil.
Efficiency Ratings
Cast-iron and steel boilers are tested to verify their heating capacity
and efficiency. Boiler ratings are published by The Hydronics Institute.
Rating indicators for each boiler model include hot water output
in Btus per hour and the Annual Fuel Utilization Efficiency (AFUE)
ratio. AFUE is determined by a testing procedure specified by the
U.S. Department of Energy. All heating equipment manufactured after
1980 is required to have a label indicating its AFUE. The AFUE ratio
is a measurement of a heating system’s seasonal efficiency, taking
into account how well the system performs over an entire season
of starts and stops. AFUE should not be confused with combustion
efficiency, which indicates how well the burner converts oil into
heat.
In many oil-heated homes, there are tags attached to the equipment
that may indicate combustion efficiency. If the combustion efficiency
is below 78, you may want to consult with an Oilheat professional.
While the unit doesn’t have to be replaced if its combustion efficiency
is less than 78, a careful analysis may indicate that you could
save energy and money by upgrading the burner, furnace or boiler.
Such an assessment would require a review of your household’s heating
oil bills, and the cost of new equipment, including installation,
to determine if upgrading to new equipment is justified.
The age of your boiler may determine its efficiency. On average,
efficiency ratings for conventional boilers 30 years old or older,
are in the mid-60% range. However, new boilers have efficiency ratings
from 81% - 92%. |
