What is comfort heating?
Why would I want to use hydronic heating?
  · Hydronic heating more comfortable
  · Hydronic systems are more efficient
  · Hydronic systems offer more versatile installations
How does a hydronic system work?
What type of equipment does a hydronic system require?
How can I find a contractor who will put in a hydronic system properly?

What is comfort heating?

A heating system that uses water to move heat, measured in Btu’s (British Thermal Units) from a heat source to the heated space is knownas a hydronic system. The most common system is often called "hot water base board heat" because most of the hydronic heating systems installed in the United States use hot water running through base board heating units to heat the living spaces of the home. Other hydronic systems use cast iron radiators or tubing in the floors, ceilings or walls to circulate heated water and radiate the heat to the living space.

Why would I want to use hydronic heating?

Hydronic heating has three advantages over other types of heating systems. These advantage are comfort, efficiency, and versatile installation.

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Hydronic heating more comfortable

Take a look at the heating system profiles below. For each heating system shown, the heavy vertical line depicts the temperature at various locations between the floor and ceiling.

Note how the Theoretically Ideal Heat Distribution line (A) is rather flat from floor to ceiling, giving you warm toes and a cool head.

Forced Air Heating (B), the most common type of system in this country, relies on air movement to heat the living space. This results in blowing air currents and uneven heating of the space: higher temperatures at ceiling height than necessary and lower temperatures at floor level. A thermostat setting of 72 degrees is usually needed for comfort.

Baseboard heating uses both radiated heat and convective air currents. Note that the temperature curve has moved closer to the ideal curve (A).

Since hydronic systems rely more on radiant heating, they offer more even heating of the living space. The hydronic floor heating example (D) has a comfort line most closely matching the ideal line (A). In a hydronic system, there’s no air blowing around the room, so there are virtually no drafts to make people uncomfortable. And because the hydronic system is heating people and things via radiating surfaces rather than hot air, the air is not getting dried out as much as with a Forced Air System. By not overheating the air, a hydronic system makes it easier to maintain a comfortable humidity level during the heating season. And note that the thermostat can be set to a lower temperature and the room can still feel comfortable.

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Hydronic systems are more efficient

Water is a great carrier of heat. Ask a scuba diver why he needs a wet suit when the water he’s swimming in is 80 degrees F. He’ll tell you that water conducts heat twenty times faster than air and, without the wet suit, he’d lose body heat too fast under water. The same goes for heating systems. Air is a good insulator but not the best heating medium.  Notice that storm windows provide insulation by having a dead air space between the two windows. Water, on the other hand, can move a lot of Btu’s from one place (where they are produced) to another place (where they can be used) very efficiently. Also, note that because more of the heat is being radiated to the living space rather than blown into it, there is less heat loss through the cracks around doors and windows than there is with a forced air system, therefore fewer Btu’s need to be produced to keep the living space comfortable.

Hydronic systems offer more versatile installations

With hydronics, you can move 40,000 Btu’s through a 3/4" copper pipe through walls and between floors - or anywhere you need the heat - quietly and efficiently. A forced air system requires a lot of duct space, about an 8" by 14" duct, to move that much air with that many Btu’s into a room. This means that zoning is easy for a hydronic system. A typical home with a heat load of 160,000 Btu’s (that’s a pretty big home) needs only four little 3/4" pipes to move all the heat it needs to four different areas of the home. You can divide that heat into bedroom zones, living areas, recreation areas, etc. simply by dividing the heat coming from your heat source into little pipes.

Talking about versatility...the hydronic heat source is usually a boiler in the basement. Boilers are tried, true and very safe. But hydronics can take heat from any heat producer, such as a solar coil, ground source heat pump or a co-generation plant. Any water cooled equipment is a potential heat source for a hydronic system.

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How does a hydronic system work?

How it works and why it works so well are closely tied together. Let’s start with why you need a heating system. Well, you need a heating system so that you can be comfortable in your home even in the coldest winter weather, but also in the milder Spring and Fall heating seasons. What makes you uncomfortable? Being in a room that’s not warm enough? Having cold feet? Being in a drafty room? All of these can make you feel uncomfortable.

When it’s cold outside, the house loses heat to the outside via conduction, convection, and radiation. How fast it loses heat to the outside depends on several factors such as how much insulation is in the walls and ceiling , how cold it is outside as compared to inside, and how hard the wind is blowing.

Conduction is the transmission of heat through a medium without perceptible motion of the medium itself. Put your hand on the hood of your car after the car has been out in the sun for a while. Your hand gets hot from direct contact with the hot metal. Convection is heat transfer in a gas or liquid by the circulation of currents from one region to another. The wind is the best example of this... warm spring breeze... cold winter wind. Radiation is the emission or propagation of energy in the form of rays, waves or particles. On a clear day in mid-winter, step out from the shadow of a building into the bright sunlight. Feels good, doesn’t it? You are being warmed by solar radiation.

Another thing to think about is that heat always moves from a warmer object to a colder one. As the house loses heat to the cold winter air, you lose heat to the house and the colder objects in it such as walls, windows, etc. To be comfortable, your heating system needs to replace the cold being lost to the outdoors. At the same time, the heat should not be drafty or create hot and cold spots in the house.

This is why a hydronic system works so well to make you comfortable. It takes the heat from the boiler or other heat source and moves it quietly and efficiently to radiators, baseboards or radiant floors, ceilings or walls. By creating these warm surfaces in each room, there is a warm object to send heat to you and the cold walls or windows. The best heating system should keep you comfortable without you even noticing it’s doing it. That’s what a good hydronic system can do for you.

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What type of equipment does a hydronic system require?

First, the system requires a heat source and, as mentioned previously, this is usually a boiler in the basement or equipment room. Why is it called a "boiler" when it only heats the water and doesn’t boil it? No one knows, but a boiler is a pressure vessel with it’s own safety controls that limit the maximum pressure in the boiler, the maximum temperature and, in many areas, a low-water cut off (see product info. or read related tutorial) that shuts off the fire to the boiler if it ever loses water due to a leak in the system.

At the other end of the system will be the heating units such as copper fin tube baseboard, cast iron baseboard, cast iron radiators (usually only found in older houses) or tubing imbedded in the floors, ceiling or walls (called RFH, or Radiant Floor Heating).

In between the boiler and the heating units are the piping and a few small but essential pieces of mechanical equipment that help make the system function quietly and efficiently. A typical system  includes:

A pressure reducing valve (see product info. or read related tutorial) that reduces the city water pressure to the lower pressure needed for the heating system.

An air separator (see product info. or read related tutorial) takes the air contained in fresh water and removes it from circulation. Water needs to be "airless" to assure a truly quiet and efficient system.

Depending on whether your system uses air control or air removal, the air separator sends the air to either a steel compression tank (see product info. or read related tutorial) through an air control fitting (see product info. or read related tutorial), or through an air vent (see product info. or read related tutorial) that takes the air out of the system. Either type of system works well and each has its advantages and disadvantages.

Air removal systems also require a diaphragm expansion tank (see product info. or read related tutorial) to accommodate the change in water volume in the system as the water heats up and cools down.

The hot water is moved through the system from boiler to heating units - and back - by small centrifugal pumps commonly called circulators (see product info. or read related tutorial). Older hydronic systems will usually have a slow speed circulator mounted on the side of the boiler pumping from the heating units toward the boiler.

If an older heating system had more than one zone, such systems usually relied on zone valves (see product info. or read related tutorial) to divide the hot water flow to each zone that required heat.

More modern systems use small individual circulators, one for each heating zone, pumping away from the connection to the compression tank or expansion tank. Circulators or zone valves are usually turned on by the thermostat in each heating zone.

Depending on the piping design, each zone may also require one or two flow control valves (see product info. or read related tutorial) in the piping. Contrary to its name, the flow control valve doesn’t control flow; instead, it prevents unwanted flow from occurring in an "off" zone when another zone is calling for heat. (Remember that definition of convection - convection can occur inside a single pipe and give you heat where you may not want it!)

Many systems today tie the thermostats into a zone control relay box (see product info. or read related tutorial) which simplifies the wiring of the thermostats to the boiler and zone valves or circulators.

For more information on hydronic components, go to the Product Information page of this web site. If you have a question about hydronic heating, contact your nearest Bell & Gossett representative.

How can I find a contractor who will put in a hydronic system properly?

First, learn about good system design. You don’t have to become an expert but you should know enough to ask a contractor the proper questions. Sources are available on this web site showing good system design - such as Bell & Gossett’s Hydro-Flo Enhanced Heating Module.

There are a number of books available.  Also, as you should, as with any contractor you hire, ask for references - and then check them out. Ask the contractor if he has any CEU credits from programs such as the B&G Design & Application School.