Hot Water Heating Systems | Hydronic Heating

There are a handful of hot water heating (hydronic heating)systems. The terms how water heating and hydronic heating can be used interchangeably.  When hot water heating was first put into use the one pipe gravity hot water system was used. Then in the 1940’s with the introduction of a circulator the two pipe system came about. The nice part about the two pipe system is that no longer did the boiler need to be situated under the heating system, as with the gravity feed system. Then today we quite often will use infloor heat through our homes, condos and apartment buildings.

Hot water heat with a one-pipe gravity feed

The one pipe hot water heat system was exactly that. One Pipe. The operation of this system was strictly with gravity. As water is heated the space between the molecules becomes greater. The greater the space means the less dense the water will be.

The pipe carrying the water would have a slight grade. The when the pipe was installed around the room the grade would allow the water to flow back to the boiler after letting off the heat to the room. The heat would be transferred from the water through the pipe to the fins. This type of heat transfer is called conduction. Then the cooler air from the floor would be heated and would rise. This creates a slight current and is called convection. The air would be controlled by dampers on the baseboard panels. If the room needed more heat just open the damper. If less then close the damper. There would still be some heat circulation at all times if the boiler was on, but the dampers did a good job of controlling the heat.

Hot water heating with a two pipe system

The two pipe system became popular in the 1940’s with the use of circulators. This changed hydronics forever. No more of having to situate the boiler under the main part of the floor for the gravity feed system. With the two pipe system you could now have better control of the heat in any room. If you needed to isolate each room or each suite you could. The way this is done (and still to this day) is by using a thermostat and a zone valve. The thermostat would call for heat and the zone valve would open allowing warm water to flow to the pipe with the fins. The room would be heated through convection heat then the thermostat would be satisfied and the zone valve would close. Each room that had a separate control would have a supply and return pipe. At the very end of the supply and return would be a small baseboard heater (usually in a hallway). This would not have a control on the heater. The loop just ran all the time that the main pump was operating. This is called a wild loop. The purpose was to make sure not to burn out the boiler.

These systems were made of black iron pipe and copper pipe. Where the water is running through the pipe in the supply and the return the pipe is black iron. Where the pipe was running through the baseboard the pipe would usually be copper tube, and the pipe with the fins was copper tube.

Baseboard heat side note

If you have baseboard heat in your home make sure to vacuum the fins every couple of months. The cleaner the fins the better the air circulation and the more efficient the system will operate. If your home is cooler then you think it should be check for dusty fins. This is the easiest problem to fix first.

Hot Water Heating Infloor Radiant Heat

Infloor heat, sometimes called radiant heat, radiant floor, or under floor heating, is the best way to control your hydronics heating system. This system is the Cadillac of heating systems. People who have allergies will find that this form of heating is far superior to all others. And for those who want complete control of their heating system will be able to do just that. From a snowmelt, infloor heat in the concrete, garage heat, and pex installed under the floor in a staple up system. All of these can be run from one boiler and can give precise control. If you like your bedroom cool, but your kids like theirs a little warmer you can do that. You can have your kitchen nice and toasty, and if the weather changes and starts to snow No More Shoveling.

Infloor heat is a series of pipes that use the floor for the heat transfer as compared with the fins on baseboard heaters.

Depending on the heat loss calculation, the type of infloor used, and the medium being used will tell you the spacing requirements. The spacing between each pipe ranges from 6 to 24 inches.

For different styles of infloor heat and for more information see radiant heat.

Check our other sections for the other parts of a hydronics heating system.

Pumps, controls, boiler, thermostats, indirect water heater, relief valve, zone valves, cross connection control device, pex pipe, glycol, copper tube snow melt, black iron, heat exchanger, low water cutoff temperature gauges, prv, aqua stat, expansion tank, boiler vs. water heater infloor heating.