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Boilers Check the altitude pressure gauge to determine whether or not there is water in the boiler. One PSI will lift water 28 inches; 4.34 PSI will lift water 10 feet. If you are inspecting a two-story house, the height of the radiators or convector baseboard heat will be 15 feet to 20 feet above the boiler. Assuming this is true, you need about 10 pounds of pressure in the system to lift water to the top of the radiators or convectors. Add a few pounds for air or water losses over the months or for bleeding.
The bottom side of the gauge, which shows altitude pressure, is a water temperature gauge. This gauge is one of the first things you should check. Inspect the area around the bottom of the boiler inside and out for visible leaks or previous stains. If the heater has been off for a long period of time, you may see considerable water develop when you turn the unit on. This may be condensation, and not a defect. Check the metal heater cabinet. Rusting and failure of the metal may indicate a failure of the sealing material between the boiler tubes. When the heat escapes from the boiler area and comes in contact with the cooler metal cabinet around the heater, condensation forms and eventually rusts out the cabinet. Repairs/sealing are possible, however, they tend to be temporary. Pressure Relief Valve Inspect the pressure relief valve for seepage, present or past. This indicates excessive pressure in the system. Possible causes:
Limit Controls Most of the systems we see will have a combination control with a high and low setting. If the system has a domestic hot water coil in the boiler, there will be a differential dial with a 15-degree range. A typical heating cycle would be as follows:
The domestic hot water control operates at the low limit and within the range set at the differential dial. Assuming the low limit is set at 150 degrees and the differential dial is set at 15 degrees. The water temperature in the boiler will be maintained between 135 and 150 degrees. This also assumes the thermostat is not calling for heat at which time the controls would respond to the heating temperatures. There are numerous limit controls on the market and just as many electrical control variations. Most newer limit controls have the burner and circulator start at the same time. Zone Valves
Expansion Tanks
In open systems, the tanks at the top of the system are at zero atmospheric pressure. If too much water is added or if too much pressure is developed in the boiler, the water is discharged harmlessly onto the roof. In closed systems, the tanks installed above the boiler have system pressure in the tank. When the system is filled, water is pushed into the tank, compressing the air in the tank. Air is highly compressible and acts as a cushion, which controls moderate pressures. These tanks can become waterlogged or fail. If they become water logged, they or the system can be drained to re-establish the air cushion. Failed tanks rust out at the top of the tank. Oxidation will occur when you have air and moisture. This condition is present at the top of the tank where oxygen is present. Water covers the bottom of the tank, where oxidation is less likely to occur. When the metal fails at the top of the tank, the warm, moist air in the tank escapes. When this air comes in contact with the cooler, dryer basement air, it will have the tendency to condense. When condensation occurs, a water droplet develops on the top of the tank. When the drop is large enough, it rolls down the tank. When this water evaporates, it leaves stains on the tank. The failures in the tank may let air out but may not be large enough to leak. The average life expectancy of a tank in a closed system is 40 to 60 years. Diaphragm tanks have a bladder or membrane, which keeps air and water separated. These tanks are relatively stable, but the air, which is separate from the water, has no place to go. This air provides a cushion for the pressure in the system. Distribution
Radiators, baseboard and radiant heat deliver heat mostly by convection. Objects absorb the energy and transform it into heat. Radiant heat is a uniform pattern of piping, usually copper in a sand bed below a concrete floor. Hot water moving through the piping warms the concrete floor and the room above. Concern with such a system is that it may leak. Because the pipes are below the floor, leaks may be undetected for months and possibly years if the heating system has automatic water feed.
If the system has an automatic water feed, you should manually turn the water off and watch the pressure. Allow ample time so you are relatively certain there is no pressure loss. Typical life expectancy of radiant distribution systems below concrete floors is 25 to 30 years. Modern radiant distribution systems are PEX piping. There are versions of this piping emerging every few years. It appears to have the attributes needed for long life. Water Heater Recovery CharacteristicsRecovery rate is the amount of water the burner can heat 100 degrees in 1 hour. This is called a 100-degree temperature rise. This does not mean raise the temperature to 100 degrees; it means 100 degrees more than the temperature it started at. Example: If a burner can take 40 gallons of water and raise its temperature 100 degrees in one hour, that burner/heater has a 40 gallon recovery rate. The Inspector’s rule of thumb: Divide the BTU rating of the burner by .00088 to determine the recovery rate. 42,000 BTU burner divided by .00088 = 36.96 gallons 75,000 BTU burner divided by .00088 = 66 gallons Hot Water Heating Checklist
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A three-story house would demand more pressure. If there is no pressure in the system, the
boiler could be damaged.
When inspecting this type of system, pay close attention to
the altitude pressure gauge. If you do
not have proper pressure, you should slow down and investigate.