Hot Water Boilers and Steam Boiler Consumer Information

People who use boilers for their main source of heat report that they love
the kind of heat that it provides. If you were thinking that there really is only one type of heat,
you may want to reconsider. All you have to do is add adjectives to the beginning of the word heat.
There is dry heat, wet heat, drafty heat, even heat, and uneven heat just to mention a few. The heat
provided by a boiler will give you even, draftless heat. That is opposed to drafty, uneven heat many
forced air systems provide.

There are many different combinations and configurations for boilers.
There are gas boilers and oil boilers and a combination of the two that are called dual fuel boilers. A boiler is simply a pressure vessel where water is heated for the purpose of providing
heat somewhere for something. There are high pressure boilers and low pressure boilers.
The focus of the boiler page is not on high pressure boilers or the type of fuel used to heat the
water, but on the mechanics of how the loops work and hot water and steam controls on low pressure
residential boilers. Many of the same controls found on gas boilers and oil boilers
are the same controls used on furnaces and water heaters. Refer to the furnace page for more info.
on gas controls. Oil controls will be introduced later.
Boilers can either be hot water or steam (either of those can be gas boilers or oil boilers)
and the piping systems are different for each type. The hot
water system boiler uses a pump to circulate the hot water while the steam boiler uses it's own
pressure to circulate the steam throughout the system. They also have some similar and some
different controls to run the boiler. Welcome to hot water boilers and steam boiler consumer information.

Aquastats

Aquastats are like thermostats except they control the temperature of the water inside the boiler. Again there are many different configurations for the way the aquastat is hooked up so we are going to stay with the basics. The aquastat has a sensing bulb that is inserted into a well
in the side or front of the boiler. This bulb senses the temperature of the water inside the
boiler. When the temperature drops below a certain set point (usually 140 degrees F.) it
turns the burner on so that the water can be heated to the maximum temperature setting on the
aquastat. The burners are then shut off until the temperature again drops below the set
temperature. These temperature settings are usually manual and are different from one type of
boiler to the next. When you turn your thermostat up you are turning the circulator pump on
(on hot water systems) so the hot water can circulate through the pipes. The hot water leaves
the boiler and makes the loop. By the time it gets back to the boiler it has lost some heat
through the heat exchange process in your radiators or baseboards (and any uninsulated pipes
under the house or in the loop). The cold return water is sensed by the bulb in the aquastat
and the aquastat again turns the burner on to reheat the return water so it may make the trip
through the loop again when the thermostat calls for heat.

The Boiler Water Source

Hot water boilers and steam boilers alike need a water source. This can either be city
water or well water supplied by a pump. This is the source for water that is fed into the boiler.
Barring any leaks, drips, or weeping in your system, the supply from the well or city is
necessary to keep the water level up in the boiler. A dry fired boiler is very dangerous and it is important to keep the water in the boiler at proper levels. For hot water systems
the boiler should be full. Steam systems are different. To much water and the mains flood.
The steam boiler will not function properly with flooded mains. A control at the supply should
keep the proper water levels in the system. At the beginning of the supply (city or well) there
should be a gate or ball valve to turn the water off to the boiler for maintenance and/or to
stop major leaks. When this is shut off the power and fuel source for the boiler should be shut
down also. After the shut off valve there should be a backflow preventer, however there may
be some older boilers that do not have backflow preventers. Current local and national codes
require backflow preventers to keep the supply water from being contaminated by back flow
water from the boiler. Older boilers are grandfathered so they do not require a backflow
preventer. After the backflow preventer there should be a pressure reducer valve. Many city
water sources (and well sources) have pressures exceeding 40 psi. A residential boiler should
not operate at pressures over 20 psi. The pressure reducer valve reduces the supply water
pressure down to 12 psi. After the pressure reducer, the source supply water should be fed into
the return loop.

The Boiler Loop

The beginning of the loop is inside the boiler at the water jackets where the water is heated.
The pump kicks on when the thermostat calls for heat and the heated water is pumped up the
loop supply line where it flows through the basebords, radiators, or coils. As it flows through
these heat exchange devices the water loses heat and flows back to the boiler in the return
line. As it gets near the boiler the water goes through the impellor which is part of the
circulator pump. Most boilers in a hot water system have the circulator pump on the
return side of the loop.

The boiler isolation valves can be turned off so that the
circulator pump can be changed without bleeding the entire loop. Maintenance can be performed
on the boiler without introducing air into the systems loop. Additionally, the air purge drains
eliminate the need to bleed air from all the baseboards or radiators.