High Efficiency Gas Furnace?

[Robert Huffman]

I have seen quite a few high efficiency gas furnaces and they all have plastic exhaust and the burners are encased and not accessible because they are behind sheet metal. Saw one today with plastic exhaust but the burners were not enclosed and easily accessible. So my question is...are the burners on all high efficiency gas furnaces enclosed in sheet metal possibly with a small glass viewing window which makes a plastic exhaust pipe permissible (because the exhaust is not so hot) or am I looking at a system where its not a high efficiency system and the plastic exhaust pipe should not have been used?

[Dom D'Agostino]

In general, you need to look up the specifics for the model in question (such as manufacturer's install requirements).

I wouldn't guess how a gas appliance is supposed to vent, without knowing what it is, etc.

[Gunnar Alquist]

I have seen quite a few high efficiency gas furnaces and they all have plastic exhaust and the burners are encased and not accessible because they are behind sheet metal. Saw one today with plastic exhaust but the burners were not enclosed and easily accessible. So my question is...are the burners on all high efficiency gas furnaces enclosed in sheet metal possibly with a small glass viewing window which makes a plastic exhaust pipe permissible (because the exhaust is not so hot) or am I looking at a system where its not a high efficiency system and the plastic exhaust pipe should not have been used?

Robert,

Without more information, I doubt anyone will be able to give you a solid answer.

I have seen some Trane/American Standard Cat IV furnaces with PVC exhaust pipe and the burners were not behind sheet metal and a sight glass. However, the cabinets on these do have a pretty stout and gasketed cover/door over the entire front of the furnace.

As Dom has already said, it is difficult to give you a specific answer without more information. Even a photo would help.

[Robert Huffman]

In general, you need to look up the specifics for the model in question (such as manufacturer's install requirements).

I wouldn't guess how a gas appliance is supposed to vent, without knowing what it is, etc.

Good advice.

[Trent Tarter]

High efficiency 90+ condensing gas furnaces can have both sealed combustion and open combustion burner assemblies. I commonly find the lower end models having open burners and the higher end ones having sealed combustion.