| In a hot water (hydronic) heating systems, water | | | | water in a hydronic system, it releases air which |
| is heated in a gas, oil, or electric boiler and | | | | becomes trapped in the convectors, preventing |
| circulated through pipes to convectors; older | | | | hot water from entering. To release this air, most |
| systems use radiators. When the thermostat calls | | | | convectors are installed with air vents, which can |
| for heat, a "circulator pump" in the boiler return | | | | be opened with a screwdriver until hot water |
| line moves water through the pipes to the | | | | squirts out.Efficiency can be improved by insulating |
| convectors, which give up heat to the rooms. | | | | pipes, or by partially closing convector shut-off |
| When the circulator is not pumping, a "flow-control | | | | valves in rooms requiring less heat. Systems can |
| valve" stops the water flow to protect the | | | | be divided into zones with one or more rooms |
| convectors from overheating.Older gravity | | | | controlled by a thermostatic "zone valve". |
| systems have no circulator pumps and depend on | | | | Alternatively, a separate circulator is sometimes |
| lighter, heated water rising in the pipes to the | | | | used for each zone, or you could have |
| radiators; and cooler, heavier water gravitating | | | | thermostatic valves installed on each convector, |
| back to the boiler.Single-pipe systems, with short | | | | but these options might be expensive.Boilers are |
| branch lines to each convector, are used in small | | | | more expensive to install than other systems, but |
| to medium-sized houses. Two pipe systems use | | | | are generally trouble-free, very efficient, and last |
| separate supply and return pipes, and are more | | | | much longer than other types of heating |
| appropriate for larger houses, because cool return | | | | systems.* Some newer systems use non-metallic |
| water from convectors doesn't pass through | | | | piping, installed in/under floors, to distribute hot |
| others. This maintains a higher water temperature | | | | water in the rooms to be heated. In some cases, |
| at far ends of the system.As heated water | | | | a domestic oil or gas-fired hot water tank can be |
| expands, an air-tight "expansion tank" on the hot | | | | fitted with a circulating pump, and the hot water |
| side of the boiler takes in the excess; and if the | | | | directed to convectors or a heating coil installed in |
| tank fills up, a "safety-relief valve" on top of the | | | | a hot air plenum.Copyright Gil Strachan - All rights |
| boiler relieves the pressure. If this valve leaks | | | | reserved.Gil Strachan is a professional home |
| under normal operating pressure, you can open it | | | | inspector, representing Electrospec Home |
| (beware of hot spray) and close it. If the dripping | | | | Inspection Services in east-central Ontario, Canada |
| continues, the relief valve needs to be | | | | since 1994. Visit to learn more about home |
| replaced.Twice a year, if the circulator pump and | | | | inspections."The Home Reference Book" |
| motor are not permanently lubricated, add a | | | | You can probably find a home inspection for a |
| couple drops of oil. If you want to work on your | | | | little less than what we ask, but you probably |
| boiler, shut off the power, let it cool down and | | | | won't find the Home Reference Book. A $60 |
| then drain the system if necessary. Older tanks | | | | value, this solutions-oriented reference tool comes |
| can be drained when they're too full, but newer | | | | free with every inspection we perform.It's the |
| "diaphragm tanks" should be drained only by | | | | first tool you should have around the house! |
| qualified service personnel.When first heating cold | | | | |