Hydronic Heating: Hot Water or Steam?
Hydronic heating systems can operate with many different types of fluids. Watter is a common one, and in some cases is used in steam form to transfer heat from a furnace or boiler to radiators which heat the home.
Any system to transfer heat depends on the principle that heat moves from an area that has higher temperatures to ones that have lower temperatures. In hydronic heating, heat is introduced in liquids in tubing that is placed below floors, at baseboards or moving through radiators.
This heat then transfers to the lower air temperature in surrounding areas, thus heating up the area through further processes of radiation, conduction and convection. The reasons for preference for hot water vs steam in hydronic heating is discussed below.
Heating Systems Using Steam
Modern hydronic heating is an offshoot of the earlier steam heating. In steam heating systems, boilers heat water to steam temperatures. Such steam rises to circulate though pipes laid on walls or in radiators. After the transfer of heat, the steam condenses to warm water, which by gravity flows back to the boiler for again being heated to steam. Such systems using steam require very careful planning of pipe sizes so that circulation is efficient.
Heating systems based on steam are also always under high pressure and this can cause leaks that are threats to safety. This means better plumbing with pipes meant to carry high pressures and thus increased costs. Hydronic systems that use steam are rarely used in floors.
Hydronic Systems Using Heated Water
Modern day hydronic systems on the other hand, use heated water itself to transfer the heat, through tubing laid down in floors or walls. The systems using hot water are much more precise and can allow heat to be sent exactly where it is needed. The pressure in such hot water systems are just those that are needed to circulate the water and will rarely cause pressure buildups that are possible in steam systems.
The tubing used to lay down such heating systems can be made from plastic tubing such as PEX, though metal pipes continue to have an edge when it comes to the efficiency of the heat transfer. Such tubing can be laid down in floors without any problems. Such installations will remain safe from the safety concerns present in high pressure systems that are found in steam heating systems. The lower temperatures for producing hot water instead of steam can also lead to savings in energy, due to the latent energy required for the conversion from water to steam.
Hydronic systems, whether using steam or hot water, never cause any changes in air pressure in rooms. Where forced air circulation systems are used instead of hydronic systems there is an increase in air pressure from the air circulation. That can lead to air being lost through openings such as cracks, and that leads to loss of heat and thus higher costs to generate the heat in the first place.