Fuel Safety Bulletin 2002-02c

The installation of a hydronic radiant floor heating system falls under the National Building Code of Canada. This Code requires that all hydronic heating systems be constructed to an engineered design.

Problems with these heating systems have occurred where the design of the system allows the water return temperature to fall below the flue gas dew point. Condensation forms in the flue gas passage, creating an obstruction or prematurely corroding the heat exchanger and venting system.

The factors that effect the life expectancy of the appliance vary. The time in which the failure occurs is dependant upon the amount of time that the boiler operates below the flue gas dew point. Some systems, will operate for a number of years before a problem is noticed, while in others, a failure will occur in the first or second year of operation. However, the units will fail in the same way.

In the beginning you will notice condensation or a build up of residue, at the joints of the venting system. On and below the burners there will be traces of iron oxide, a rust formed by a chemical reaction between the condensed products of combustion and the material of the heat exchanger. As the rust forms, particles flake off and fall on to the surface of the burner, creating an obstruction at the burner.

Flame impingement, due to a build up of oxides on the burner, may cause the burner to produce carbon monoxide. Particles of carbon will accumulate on the heat exchanger and further add to the restriction within the flue gas passage.

Both carbon and oxide particles will accumulate on the heat exchanger, these particles will eventually restrict the flue gas passage, causing flue gas to spill into the building. The unit will start to spill a small amount of flue gas and, if left unchecked, the restriction will progressively worsen until the flue gas passage becomes completely blocked.

Hot products of combustion, spilling from the front of the unit, may cause a further malfunction by burning the control wiring or damaging the gas valve.

Individuals exposed to the flue gas may experience respiratory problems, irritation of eyes and throat, nausea and, under extreme conditions, death.

Finned Tube Type Heating Boilers are especially susceptible to condensation.