Hydronic Heating
By Kenton Shepard
Hydronic heating uses a hot fluid for space-heating. Fluid is typically heated by a boiler, then circulated by pumps through pipes installed in floors, distributing heat as it goes. Depending on the system, this liquid may be water, steam, or some other fluid designed to carry heat efficiently and help prevent corrosion.
Heat is commonly distributed in rooms in one of two different ways…
RADIANT IN-FLOOR HEATING
Radiant in-floor heating systems distribute a hot fluid through flexible tubing which can be embedded in concrete slabs or fastened to the underside of sub-floors. This system is designed to heat the home by transferring heat from the tubing to the flooring material, which then radiates heat into the room.
One of the advantages of radiant heating is that it doesn’t pressurize the home as a forced air furnace can. Positive pressure inside the home forces warm air out of the home, and replacement air must be heated, raising heating costs.
A radiant floor also heats spaces more evenly, since almost the entire floor is a heat source.
A typical arrangement with a modern high-efficiency wall-hung boiler (notice the white plastic vent and condensation tube). This home has 11 heating zones, each with its own shut-off valve and thermostat. Most homes will have fewer zones.
The hot fluid supply manifold is the set of pipes on the left, with shut-off valves. The manifold on the right is the return for cooled fluid. Circulation pumps (visible at the base of the return manifold) are usually on the cool side to increase pump lifespan.
The required expansion tank and air valve are visible at the left. The pressure gauge should read between 5 and 25 PSI, the temperature gauge should read between 165 and 185 deg. F.
Radiant floor heating: pipes are fastened to the underside of sub-floor before they connect to a return maniifold.
Radiant In-floor: Turn it on Early
If a radiant in-floor heating system installed in a home is turned off for the cooling season when an inspector arrives, the thermostat should be turned up as soon as the inspector arrives. These systems typically take a while to raise floor temperature, particularly when they are installed in concrete slabs, and inspectors will need to confirm proper operation.
HOT WATER BASEBOARD
This heating system uses a hot fluid distributed through pipes to baseboard heaters installed in various rooms in the home. The length of pipe exposed to room air is determined by the room heating requirements.
Pipes are fitted with an aluminum sleeve with fins which increase the radiant surface, allowing more heat from the pipe to radiate into the room. These fins are easily damaged and damaged fins will make noise from thermal expansion and contraction as they heat and cool. These fin assemblies are called “convectors”.
In homes in which heating pipes have been attached to floor framing with fasteners which hold pipes against joists, creaking from thermal expansion of the pipes may be heard after the thermostat is turned up.
  
As hot fluid moves through the pipe, heat is transferred by conduction to the fins, which radiate it into the room.
Insulating Visible Hot Water Pipes
Hot water pipes should be insulated where they pass through areas they are not intended to heat.
All photos by Kenton Shepard |
