2009 IMC Section 804.3.6 Exhauster connections

[Coder]

I was asked to go look at a new furnace install today (which requires a permit but did not have one). That is another story. The scenario is both a fan assisted exhaust type furnace and an indirect (passive) drafted hot water heater are both connected to a Y-pipe connector and then to the final vertical (unknown type)vent up and out of the house. Sorry no pictures yet. I told the installer that this type of set up is prohibited according to 804.3.6. He then asked if he could install a power assisted fan on the hot water heater side to fix the problem. Assuming that both fans would kick on when the furnace fired up. I am not sure if this would be a safe solution or not. Anybody? :cowboy

 

[Coder]

I was asked to go look at a new furnace install today (which requires a permit but did not have one). That is another story. The scenario is both a fan assisted exhaust type furnace and an indirect (passive) drafted hot water heater are both connected to a Y-pipe connector and then to the final vertical (unknown type)vent up and out of the house. Sorry no pictures yet. I told the installer that this type of set up is prohibited according to 804.3.6. He then asked if he could install a power assisted fan on the hot water heater side to fix the problem. Assuming that both fans would kick on when the furnace fired up. I am not sure if this would be a safe solution or not. Anybody? :cowboy

No code section to cover this.

 

[Builder Bob]

Not a good idea... Don't beleive that you can intermix power assisted with draft appliances. Not sure that the manufacture's testing of the water heater ould recommend a power assisted blower.....In other words, if the furnance is running, the draft thru the water heater's ignition area may not ever light if the fuel gas is sucked away from the ignition source....

 

[markw]

No code section to cover this.

Sure there is-if both appliances are Cat. 1 and have proper size b-vent/connectors and combustion air. G2428 IRC

 

[Coder]

Sure there is-if both appliances are Cat. 1 and have proper size b-vent/connectors and combustion air. G2428 IRC

Thanks markw. Fairly newbie at fuel gas fired appliance installs and not sure what is right or wrong. Did tell the contractor to not put a blower on the old hot water heater.

 

[klarenbeek]

For fuel gas appliances, don't go out of the IMC, that is for anything other than propane or natural gas appliances. Go to the IFGC (or fuel gas portion of the IRC).

An exhauster as described in IMC 804.3.6 is a fan added to a chimney/vent system, not a fan of a fan assisted appliance. Like Markw said, as long as both appliances are Cat. 1 appliances, they can be vented together. Do not put a power assist fan on the water heater, then you will have the situation prohibited by the section you cited. The IFGC has as similar section. You do need to find out what the vertical vent is made of. If it is a clay-lined masonry chimney, it is very likely that it won't pass from the vent sizing charts. The contracto may need to drop a metal liner down the chimnet if that is the case.