To repeat, 100% of the heat that is created is brought into the space you are intending to heat. This is also true when considering the waste heat created by the fan motor, since that heat also ends up in the heated space.
Gas furnaces are a different beast altogether.
Since this is going on:
We cannot treat it like an electric furnace unless you want to wear one of these stylish head pieces around your house 24/7:
Your average natural gas exhaust contains: Benzo-a-Pyrene, benzene, toluene, carbon monoxide, soot, formaldehyde, radon gas, radon daughters, PCBs, DIOXINS, FURANS, dust, rust, olefins, waxes, tars, oxides, sulfuric acid, mercaptans, marticulates, oils, and lots of water vapor.
A rather intimidating list, but still shorter and relatively safer than the list you will find from burning coal. Which wasn't all that long ago.
Lots of these chemicals in your home will cause death, especially the carbon monoxide. Relatively small amounts of these in your home may cause flue-like symptoms. So if you have an old gas furnace and often feel sick in the winters you may want to have your unit serviced. Even if it costs you money to fix it. (Check with your local CAP if you absolutely cannot afford to service your unit.)
Without getting into too much detail your furnace is designed to exhaust these poisonous fumes out of your flue. Like the blue arrow in this picture:
Your furnace is designed to keep those gases separate from the air being circulated in your home. Much like putting your hands in the smoke of an open fire, the exhaust gas can be very hot still. For you all using gas furnaces to heat your homes, that is lost heat. The heat leaving your flue with the poisonous gasses is lost efficiency, because it does not end up in the space you are intending to heat. Furnaces are rated based on what % of the heat ends up in your home.
Older furnaces generally range between 50% and 70% efficient, meaning some furnaces push half the heat out the chimney.
Newer, high efficiency furnaces, can perform above 90% efficiency. These furnaces actually pull the heat out of the water vapor before they exhaust the air. Then they pump the water out separately from the air. At that efficiency the exhaust air is cool enough to vent thru PVC pipe like in this example:
At the price of natural gas these days furnace upgrades are getting shorter and shorter paybacks. I do not know enough about different models and manufacturers to recommend one over another, but I can tell you that upgrading your 70% furnace to a 90%+ is likely to have a much shorter financial payback than any of the new fangled solar electrical panels.
But they sure do look nice, don't they?
Wait. How did this picture of Jackie end up with the solar ones? Hmmmm, too late to take it out now I already posted.
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