Boilers, an old standby in the Northeast, are becoming more popular around
the country with the advent of radiant, hydro-air, and hybrid systems. Instead
of heating air, a boiler heats water.
The classic boiler system uses hydronic distribution. Water is heated by
the boiler and pumped through pipes to hot water radiators or baseboard
fin-tube convectors to heat the house. Some older systems use a boiler to
make steam, which expands to fill steam radiators without the need for a
Radiant Floor Heating
In the past decade, built-in radiant floor hydronic systems
have become quite popular. Quiet and out of sight, they employ
specialized flexible tubing embedded in concrete slabs or framed
flooring systems, turning the entire floor surface into a cozy,
low-temperature radiator. When properly designed and installed,
radiant floor systems provide reliable, even heat with unsurpassed
comfort. Radiant heating is commonly touted as an energy saver,
because people are comfortable at a lower thermostat set point.
However, recent research has shown no significant difference
in thermostat settings between radiant floor houses and others,
suggesting that energy savings are largely theoretical.
Staple-up radiant floor systems, such as this
one, provide the benefits of a cozy, warm floor in wood-frame
structures. Other systems embed the tubing in a lightweight
gypsum slab poured over a framed floor or concrete slab. Radiant
floor systems must be insulated very carefully so the heat
goes only where it’s wanted.
Boiler maintenance is similar to that of a gas or oil furnace, but there
is no blower fan to clean. Oil boilers should be serviced once a year, while
gas boilers should be serviced every two to three years.
Any swishing or gurgling sounds that you hear in the radiators indicate
air trapped in the system, which reduces heat-exchange efficiency. A service
technician can bleed out the air and show you how to do it if it is needed
Occasionally, bleed valves may need to be installed or replaced. The technician
should check the hydronic system pressure and expansion tank; the smallest
leak anywhere in the system should be repaired immediately to prevent corrosion-causing
oxygen from being brought in via makeup water connections.
Gas or Oil Boiler
Boilers heat water, which is circulated throughout the house
to deliver heat. Valves or individual pumps may control the flaw
to separate zones in the building. Occasionally, Euro peon- style
hardware is used for continuous circulation and individual thermostats
mounted on each baseboard. In the popular fin-tube baseboard,
a copper pipe runs through the middle of an array of aluminum
fins; the large surface area of the fins provides heat transfer
to the air. The air moves through the baseboard by natural convection:
Cool air is drawn in from the bottom and the heated air rises and escapes from the top. Older houses may have cast-iron hot
water radiators; recently, European-style wall radiators have
become popular. All three are shown here, though they ore not
usually mixed in the same house.
Components of the above boiler: Fuel burners and heat exchanger heat water circulating through the boiler;
Fin-tube baseboard radiator heats by convection; Heated air rises
from the baseboard; Cool room air is drawn in; Pumps or zone
valves control the circulation of hot water throughout the system;
Expansion tank; Cast-iron radiator heats by convection and radiation;
Low-profile wall radiator heats by radiation and convection;
Hot water at 180°F (typical) Return water at 150°F (typical).
Boiler controls and upgrades
A typical hot water boiler operates throughout the winter with a water
temperature determined by the Aquastat, or low limit, setting (an Aquastat
is like a thermostat that senses the water temperature inside the boiler and shuts off the burner when the water is hot enough). Boiler controls
may maintain full boiler temperature throughout the year, which is very
inefficient but necessary if a tankless coil water heater heats the domestic
hoi water. In the absence of tankless coil, typical boiler controls may
be set either to maintain constant boiler temperature all winter or to shut
down and let the boiler cool off when not in use. Clearly, the latter is
more efficient and is the preferred configuration.
Electronic pilot ignition may be installed on gas boilers and furnaces.
Another improvement that can save boiler energy is installing a mechanical
vent damper. This device closes off the flue pipe after the burner shuts
off, stopping the flow of heat through the heat exchanger and up the chimney
It costs $125 to $350 installed. I don’t recommend gravity-actuated vent
dampers that depend on the heat from the burner to stay open; they are much
more likely to contribute to backdrafting. (Vent dampers are not much benefit
to a furnace; a low fan-off temperature setting allows the fan to carry
most of the residual heat into the house after the burner stops.)
A new oil boiler may have an efficiency rating of 84% or higher.
Every hydronic radiator should have a bleed valve, which can
be opened slightly with a screwdriver or a special key to let trapped air
This vent damper automatically opens when the boiler fires,
then closes when the burner shuts down, reducing the amount of heat lost
through the chimney.
PRO TIP: When air-venting doesn’t work
properly on a steam-heating system, it can lead to uneven heating,
large temperature fluctuations, and discomfort
CAUTION: common problem with team systems is too much pressure.
The boiler pressure controls should be set just high enough so
that the boiler shuts down just as each radiator fills with steam.
Too much steam pressure increases the boiler’s cycling losses and leads to over heating. That can particularly be a problem
if the building envelope’s efficiency is improved dramatically and /or some radiators are removed during remodeling. Timed-cycle
controllers vary the boiler cycle length to match the outdoor
temperature, further improving the system’s efficiency.
TRADE SECRET: If you have an oil-fired boiler or a furnace with
a standard, inefficient oil burner, have a technician replace
the burner with a flame-retention burner. Those units, which
cost about $400 to $500, do a better job of mixing the oil with
the combustion air, which better controls the fire. They also
reduce the amount of heat lost up the chimney, bringing the overall
Steam boilers are very different from hot water boilers. Steam systems
were popular in the early 20th century and many of them are still in service
in older homes. Instead of relying on pumps to circulate hot water, steam
boilers boil water to create steam. The steam naturally expands to fill
all the pipes and radiators in the system, distributing heat throughout
the house. Although steam-heat distribution is simple and reliable, steam
boilers have a number of unique maintenance and efficiency issues.
Most residential steam systems are one-pipe systems. When the thermostat
calls for heat, the boiler fires and steam begins expanding to fill the
system. As the steam expands, it displaces air contained in the pipes and radiators, and that air must be allowed to escape through air vents typically
located at the top of each steam radiator. Once the steam reaches the radiator,
the air vent senses the heat and closes, keeping the steam inside. As the
steam emits heat through the radiator, it condenses to water and flows back
via gravity through the same pipes to the boiler.
Both hydronic and steam-boiler systems can benefit from insulating
distribution pipes, particularly in unconditioned basements and crawl spaces. Be sure to install insulation neatly, and miter
the corners to minimize pipe exposure. Use a good-quality tape,
where necessary, to hold the insulation in place and keep the
seams closed. Wrap the tape several turns around the insulation;
don’t just run it lengthwise along the seam. and for safety’s
sake, don’t disturb any boiler piping that appears to have asbestos
insulation on it already.
Pipe insulation is inexpensive and widely available
at hardware stores and home centers. Make sure the material
used on heating pipes is rated to at least 180°F, because some
types will melt on heating pipes.
High-density fiberglass pipe insulation is
more expensive but necessary for the high temperatures found
in steam systems. Be sure to measure the pipes carefully when
ordering the insulation. Due to the large, awkward fittings,
it can be difficult to cover all the elbows and tees in a steam
system, but do as much as you can.
Duct or pipe insulation that contains asbestos
(the material on these steam pipes) can be dangerous if it’s
disturbed or falling apart. Airborne asbestos fibers can lead
to lung cancer and other diseases.
Air-venting systems that aren’t working properly can lead to uneven heating,
large temperature fluctuations, and discomfort. A tune-up can increase energy
efficiency and comfort dramatically. If the air vents are too small, if
there are not enough of them, or if they are clogged with mineral deposits,
air gets trapped in the system, and the steam can't reach its destination.
Having a professional replace malfunctioning air vents, add extra vents
to radiators, and add special high-volume air vents to large central supply
pipes can improve steam-system efficiency by quickly get ting the heat where
it is needed. Thermostatically controlled vents can reduce the rate of steam
delivery to some rooms, reducing overheating and improving overall comfort.
Two-pipe steam systems (less common in residences) have a separate condensate-return
Instead of air vents, two-pipe systems have a steam trap at each radiator.
Steam-trap maintenance is critical for proper operation, and all the steam
traps in a system should be replaced or rebuilt at the same time, not one
In addition to the standard cleaning and tuning that every boiler or furnace
requires regularly, many steam systems need periodic adjustments to the
water level, which is typically done by the homeowner. Steam boilers also
need regular water maintenance; periodically, boiler water should be drained
to remove sediment and rust. Chemically treating steam-boiler water reduces
corrosion and improves steam distribution efficiency. Steam-boiler water
maintenance should always be performed by technicians with experience in
local water conditions and steam maintenance.
TIP: If you are planning to replace
an old heating system with a new, energy-efficient one, stick with
the same fuel- and heat-distribution system
CAUTION: Atmospheric vented combustion equipment depends on
waste heat to carry combustion byproducts up the chimney. That
waste heat is one of the major sources of inefficiency in old
furnaces and boilers. New, high-efficiency equipment wastes much
less heat. Cool chimneys can condense water, potentially damaging
the structure and the equipment. Old masonry chimneys can be
retrofitted with aluminum or stainless-steel liners, which eliminate
condensation and improve draft velocity (they should be installed
by a professional). Many new furnaces and boilers can be vented
directly through a sidewall or band joist, eliminating the need
to upgrade an old chimney. Be careful if you upgrade your furnace
or boiler; an atmospheric hot water heater left alone to vent
through an old chimney may also cause problems.
Zoning Distribution Systems
Dividing a house into multiple heating zones, each with separate
thermostatic temperature control, is often considered an energy-saving,
as well as a comfort, feature. The theory is that people may
lower the thermostat independently in parts of the house they
are not using, reducing heat loss from those areas. Whether this
saves energy depends entirely on people’s habits, The simplest
form of zoning is the installation of more than one heating system,
each serving a section of the house with its own thermostat.
In homes with electric baseboards, each room is usually a separate
zone. Newer two-story homes often have a separate furnace and air conditioner to serve each floor.
Individual heating systems can be divided into separate zones
with varying success, Hot water boilers can easily be zoned with
separate circulator pumps and piping; residential steam systems
are pretty much impossible to zone. Furnaces and heat pumps can
be zoned with special dampers that block airflow to various sections
of the house, but those installations typically suffer efficiency
problems. All ducted heating systems, especially heat pumps,
depend on adequate airflow, When only one zone calls for heat,
the airflow is choked off and efficiency suffers dramatically.
One way around this problem is to install multi-speed equipment.
Some high-end furnaces have modulating burners, the best heat
pumps have dual-speed compressors, and both have variable-speed
blowers, Those features allow the equipment to run more efficiently
when there is only partial demand. They even improve the efficiency
of single-zone systems by matching the equipment output to the
load in mild conditions.
or Replacing Heating Equipment
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