A high efficiency furnace uses a different type of venting system because it extracts the heat that remains in those combustion gases before venting the resultant mixture of water and carbon dioxide.
High efficiency furnace exhaust temperature.
Conventional low efficiency furnaces have exhaust temperatures commonly in the many hundreds of degrees and conditioned air exit temps at the up to 250 300 degree range at times whereas high efficiency furnaces extract more of the heat from the combustion so the exit temperature is much lower to the point that in very high efficiency furnaces the exiting combustion gases and conditioned air may both be around 100 150 degrees.
High efficiency or condensing furnaces exhaust the combustion gases and bring in fresh air through pvc pipes to the outside usually routed through the sidewall of the house.
It uses a venting system to extract that heat before venting.
As a result natural draft furnaces struggle to reach efficiency levels above 70 percent.
A standard efficiency furnace provides 80 annual fuel utilization efficiency afue.
Differences between 80 and 95 furnaces.
When this temperature starts to exceed 130 degree f it is usually an indication that there is a problem.
High efficiency furnaces use draft inducers.
In this type of furnace 20 of the energy produced by natural gas is expelled as exhaust.
These highly efficient furnaces have a heat exchanger and a condensing chamber that help maintain a considerably low temperature on the pipes.
It is classified as type bh venting.
A high efficiency condensing furnace can achieve efficiency ratings of 90 or above.
You can capture that heat with a high efficiency condensing furnace.
When outdoor temperatures drop into the 20 s or below.
Venting for high efficiency gas furnaces materials.
Such furnaces cost more to run since they fail to capitalize on a significant amount of energy.
I think we in new england are going to see pvc failures in the near future directly related to the high flue gas temperatures of the new high efficiency boilers.
A higher efficiency furnace with 90 to 98 efficiency is significantly more efficient than an 80 efficiency furnace and should produce slightly cooler exhaust.
These days 95 afue is a common rating among new gas powered furnaces.
High efficiency furnaces offer 90 or more afue.
The high temperature of flue gases is a major concern to me due to the fact that schedule 40 pvc pipe and fittings are only rated for 140 degrees fahrenheit.
Due to the condensing nature of a high efficiency furnace its venting must be made of a material that is resistant to corrosion.
A conventional furnace vents these combustion gases through a vertical exhaust system that is attached to the furnace.
Even when designed correctly a natural draft flue system has certain limitations in terms of drafting speed.
This usually equates to a median pipe material temperature value of 86 to 100 degree f.
