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This glossary defines the plumbing, heating, water and ground terms used in this manual, one sentence each, with the section where each one matters most.

AFUE Annual fuel utilization efficiency, a furnace or stove's rated share of fuel energy that ends up as heat in the house over a season, covered for wood and pellet stoves in §8-2. ### Air gap An open space of air between a water outlet and whatever it fills, one of the accepted ways to keep a cistern from contaminating a public supply, §3-1. ### Backflow Water running the wrong way through a pipe, which can carry irrigation water or anything else into drinking lines, §5-1. ### Bleed-off A small steady drain on a swamp cooler that carries away minerals, and which should drain no more than necessary, §9-1. ### Btuh British thermal units per hour, the rate a gas appliance is rated in, and a figure that falls with elevation, §8-3. ### Cistern A large drinking-water container on a roof, underground or beside a home, which you check from outside and never enter or lean into, §3-1 and §3-3. ### Coliform A group of bacteria used as a warning sign in a water test, since a high total count suggests harmful germs may be present, §2-3. ### COP Coefficient of performance, the units of heat a heat pump delivers for each unit of electricity it uses, §8-4. ### Creosote A highly flammable deposit that builds up inside a chimney and is the reason for a yearly professional cleaning, §8-2 and §E-6. ### Cross-connection Any link between a drinking-water line and something that could contaminate it, such as an irrigation system or a pool, §5-1. ### Derate To run a gas appliance at a lower input than its sea-level rating because of elevation, which is a licensed professional's job, §8-3. ### Ditch rider The person who runs water deliveries along a ditch or canal system and whose notices tell you when you may draw water, §5-1 and §5-2. ### Drainfield The buried area where a septic system's liquid goes into the soil, which must stay free of vehicles, concrete, trees and vegetable gardens, §6-3. ### Easement The legal right of a ditch's owner to enter and maintain a strip of your land, as wide as reasonably necessary, §5-1. ### E. coli A bacterium whose presence in a water test suggests human or animal waste has reached the water, so use safe water and contact the health department, §2-3. ### Exempt well A category of small well in Colorado law that still needs a State Engineer permit, so read your own permit to see what it allows, §2-1. ### Expansion tank A small tank that gives heated water somewhere to go in a closed system, and whether you need one is your plumber's call, §8-3. ### Float valve The valve that stops water filling a swamp cooler tray, and a sticking one runs continuously, §9-1. ### GFCI Ground-fault circuit interrupter, the protected type of outlet or breaker that CPSC says a heat tape should be on, §7-2. ### Grain per gallon A unit of water hardness [equal to 17.1 mg/L](http://region8water.colostate.edu/PDFs/Well%20Educated/Revised%20Fact%20Sheets%20-%20Nov%202012/Corrosivity%20&%20Hardness%202012-11-27.pdf), §4-2. ### Hardness The calcium and magnesium dissolved in water, measured in mg/L or grains per gallon, §4-2. ### Heat tape An electric cable fixed to a pipe to keep it from freezing, which must be certified and used exactly as its maker says, §7-2. ### Heating degree days A yearly tally of how far daily temperatures fall below a set base, used to compare how much heating a place needs, §1-3. ### Mancos Shale The rock formation that is the primary selenium-bearing formation in western Colorado and also a source of swelling soil, §2-4 and §6-1. ### Odor fade A loss of propane's added smell in soil, concrete, drywall, wood, or new pipes and tanks, which is why even a faint smell counts, §8-1 and §E-1. ### Pre-charge The air pressure set inside a well pressure tank, which you watch through the gauge and leave to a licensed professional to change, §2-2. ### Pressure switch The electrical switch that starts and stops a well pump, which homeowners should not adjust, §2-2. ### Pressure tank A tank that stores pressurized water so a well pump starts less often, §2-2. ### Regulator The device on a propane system that controls gas pressure, which you keep clear of snow with a broom and otherwise never touch, §8-1. ### Relief valve The safety valve on a water heater that releases excess pressure, and it must never be removed or plugged, §8-3. ### Reverse osmosis A treatment that pushes water through a fine membrane, usually at one tap; test your water before and after, since no home unit's result can be assumed, §2-4. ### RP assembly A reduced-pressure backflow device, tested yearly by a certified technician, which CSU says is required where one system delivers both irrigation and drinking water, §5-1. ### Selenium A natural element needed in small amounts and harmful in high amounts, and the only way to know your well's level is a lab test, §2-4. ### Shock chlorination A one-time heavy dose of chlorine used to disinfect a well, which is a contractor's job after any flood, §2-3. ### Swamp cooler

A cooler that uses evaporated water to cool outdoor air, also called an evaporative cooler, §9-1 and §9-2.