Gas heating appliances are rated according to their Annual Fuel Utilization Efficiency, or AFUE; the higher the AFUE rating, the more efficient the unit. The current minimum rating required by federal standards is 80 AFUE. The minimum rating for Energy Star compliance is 90 AFUE.

S.E.E.R. stands for Seasonal Energy Efficiency Rate. A.F.U.E. stands for Annual Fuel Utilization Efficiency and H.S.P.F. stands for Heating Seasonal Performance Factor. These are the most commonly used terms to describe equipment efficiencies. The higher the number, the better. See similar questions...

AFUE is a term created by the Department of Energy. It stands for "Annual Fuel Utilization Efficiency". It is used to measure the amount of gas consumption of a furnace. As an air conditioner with SEER ratings, the higher the AFUE the greater the efficiency for a furnace. The minimum allowable AFUE is 78%. For every $.78 spent on gas to heat your home, $.22 is wasted as it goes up the flue. We recommend you consider an AFUE of 90%-95% when replacing or installing a new one. See similar questions...

The least efficient gas furnace available today has a AFUE of 78%. All furnace manufacturers today build two efficiency ranges of gas furnaces. Their standard gas furnace will be between 78%-81% efficient (called "80% AFUE") and their high efficiency gas furnace will be between 90%-96% efficient (called "90% AFUE). To be practical, most homes will have some factor that will justify one efficiency range or the other. In very few homes are both efficiency ranges equally practical. See similar questions...

SEER is Seasonal Energy Efficiency Rating. It's basically a benchmark that tells you how efficient a piece of equipment may be. Mostly you would use this rating when comparing different brands of equipment, to ensure that you're comparing similar products. A SEER is an indicator of how much electricity you can expect the unit to use - the higher the SEER, the more efficient the unit, and the less power it consumes while cooling your house. See similar questions...

Isotonic solutions cause no swelling or contraction of the tissues with which they come in contact, and produce no discomfort when instilled in the eye, nasal tract, or other body tissues. See similar questions...

The tonicity of the solution is less than that of the cells. When this occurs, water enters into the blood cells causing them to swell and finally burst, with the liberation of hemoglobin, or water invasion of the body’s cells. If this invasion is beyond the body’s cells, then water intoxication results, with convulsions and edema. See similar questions...

The tonicity of the solution is greater than that of the cells, which can cause a variety of complications, such as, hyperglycemia, intracellular dehydration, loss of water and electrolytes, dehydration and coma. See similar questions...

Here a "hack" is a clever shortcut or a lesser-known, faster way to get something done. A hacker believes that information-sharing is a powerful positive good, and that it is a hacker's duty to share her expertise—so we will. See similar questions...