GoGeisel.com - HVAC and Plumbing Glossary

Throughout our site we use many technical terms and industry specific language.

It can be confusing. Use this glossary to get a more detailed explanation.

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Glossary of Heating, Air Conditioning and Plumbing Terms

Alphabetical Index of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

AFUE	This is a percentage measurement of a furnace's heating efficiency. The U.S. Government's minimum efficiency level is 78%. The higher the AFUE, the more efficient the furnace. The initials stand for Annual Fuel Utilization Efficiency.
AGA	American Gas Association
Air Handler	This is the indoor section of a split system. It can be a dedicated air handler, or could be your furnace. Also known as a fan-coil.
Ambient Temperature	The average temperature of the atmosphere in the vicinity of an appliance
Anode Rod	A sacrificial rod composed of one or more metals installed in the water heater that protects the tank from corrosion helping extend the life of the tank
Anti Scald Valve	Device used to prevent high water temperature
ASHRAE	American Society of Heating Refrigeration Air Conditioning Engineers
ASME	American Society of Mechanical Engineers

Back Flow	When water travels from one system back into any part of the main distribution system
BTU	British Thermal Unit. This is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. You'll see this measurement when you look at heating and cooling capacities - for example, your dealer may re commend a 75,000 Btu furnace and a 24,000 Btu air conditioner for your home.
Burner	A heat producing device where the flame or heat is produced

Check Valve	To allow fluid to flow in only one direction in a pipe; also known as back flow preventer
Closed System	A system where the incoming cold water supply has a device that will not allow water to expand when heated (i.e. check valve, back flow preventer, some pressure reducing valves)
Combustion Chamber	The location where combustion takes place.
Commercial Application	Water heaters used for more than a single family dwelling
Condensation	Formed by more heat being absorbed into the water leaving less temperature to carry the water vapor produced in gas combustion to pass out of the venting system
Condensing Unit	This is the outdoor section of a split system air conditioning system. You'll know it best as the air conditioner that sits outside your home.

Degree Rise	Difference between the starting water temperature and the ending temperature after heating is complete
Dielectric	A nonconductor of direct electric current
Dip Tube	Tube inside the water heater that sends cold water to the bottom of the tank
Direct Vent	Pulls outside air for combustion and vents combustion gases directly outside
Draft Diverter	A device fitted in the flue way of a gas appliance to prevent updraft, downdraft or the secondary flue blockage from obstructing the escape of products of combustion or otherwise affecting the normal operation of the appliance
Drain Valve	Device designed to allow drainage of stored contents from a water heater
Dual element heater	An electric water heater with an upper and lower element for heating water

Efficiency	A products ability to utilize input energy; expressed as a percentage
Energy Guide Label	The Federal Trade Commission (FTC) requires that gas, electric and oil residential automatic storage water heaters be labeled to show 1.) an estimated annual cost of operation for that particular model, based on a national average cost of fuel specified by FTC and 2.) how the efficiency of that model compares to all other comparable models
Evaporator Coil	If your furnace is the air handler section of your split system, then you'll need an indoor coil added to your furnace to complete the system. The coil transfers heat to give you cool air and also aids in dehumidification. - If your furnace is the air handler section of your split system, then you'll need an indoor coil added to your furnace to complete the system. The coil transfers heat to give you cool air and also aids in dehumidification.
Expansion Tank	Designed to absorb excess pressure due to thermal expansion, e.g. closed system

First Hour Delivery (Rating)	Combination of the usable stored volume of hot water in tank, plus the recovery capacity for the first hour of operation
Flow control valve	Device designed to reduce water flow (GPM) to a plumbing fixture (i.e. shower head at 5 GPM vs. 2.5 GPM); the use of flow control valves can be cost effective in load calculations, reducing the water usage and the amount of energy used to heat water
Flow rate	Rating in gallons per minute (GPM) or gallons per hour (GPH)
Flue	A passage way for products of combustion
Flue Baffle	A device to deflect, check or regulate flow through the flue
Flue Damper	Minimizes convective heat loss through venting system
Foam Insulation	The insulation surrounding the surface of the water heater tank
Foot Print	The area of space taken up by the water heater

Galvanic Action	If two unlike metals are immersed in an electrolyte, an electrical potential will exist between them; if the two are in electrical contact, an electrical current will flow; the metal which becomes the anode of this cell will corrode and dissolve while the cathode will be protected from corrosion
GPH	Gallons Per Hour. You might see this rating if you are looking at an oil furnace or water pump sizing chart. In addition to input and output, an oil furnace also has a rating of gallons per hour, the volume of oil a furnace is capable of burning in 60 minutes. Most water pumps are sized in Gallons per hour.
Gas Control	Device use to regulate gas pressure on a water heater

Hard Water	Natural waters contain impurities in various proportions; traditionally hardness is a measure of calcium or dissolved solids in a solution. Below is a list of types of hardness and their referenced parts per million range
	Type	Hardness

	Soft	0-49 ppm
	Fairly soft	50-99 ppm
	Fairly hard	100-149 ppm
	Hard	150-249 ppm
	Very Hard	250 plus
Head LOSS	The pressure of water as measured at a stated point; it may be measured in feet or in pounds per square inch (PSI)
Heat Exchanger	A heat transfer system
Heat Pump	A unit that both cools and heats your home. A heat pump system can be either a split system or a packaged system. A heat pump can be used in conjunction with a gas/oil/LP furnace (using the furnace instead of electric resistance heat when temperatures fall below about 35 F) with the addition of a fossil fuel kit.
Heat Transfer	When heat is passed from one medium to another
Heat Trap	Restricts heat loss through water connections to a tank
HSPF	This is a measurement of a heat pump's heating efficiency. There is no governmental minimum rating. The higher the HSPF, the more efficient the heat pump's heating performance. HSPF stands for Heating Seasonal Performance Factor.
Humidistat	Wall mounted control which powers and regulates your home's automatic humidifier.

Immersion	Referring to something submerged in water
Incoming (Inlet) Temperature	Temperature of water entering the tank
Input	The amount of fuel used by a gas appliance in a given period of time: generally rated in 1 hour
Instantaneous Water Heater	A type of water heater that heats water as it flows through a heat exchanger coil

Junction Box	Utility area where incoming current is connected in a water heater

KW - kilowatt	A measure of the rate of supply of energy or power, and is equal to 1000 watts or 3412 BTU per hour

LP	Liquid Propane - A fuel for gas water heaters

Manifolded Installation	Paralleling of water heaters for large hot water demand applications
Mixing Valve	Mixes hot and cold water to achieve a specified delivery temperature

Natural Gas	A fuel used with gas water heaters
NSF	National Sanitation Foundation

Oil Powered	A water heater that uses oil as its fuel source
Operating cost	The cost of running a water heater for a given time period

Packaged System	Packaged units provide both heating and cooling from one unit that is placed outside the home - on the ground, on the roof, or sometimes mounted through the walls of the building. Packaged units come in several combinations of fuel sources - gas heat/electric cooling; heat pump; electric heat/electric cooling; oil heat/electric cooling.
Parallel System	Two or more identical size heaters piped with water connections, that is, cold water travels equal distance into the inlets of the heaters from a "t" connection and hot water travels equal distance from the outlet of the heaters to a "t" connection
Peak Hour Demand	Time when the largest demand for hot water is needed
Peak Load Period	That period of the day when the system has the greatest demand
Pilot	A small burner used to ignite the main burner
Point of use	Small water heater used for remote locations water heater
Power Venting	Mechanical draft exhaust to outside, usually utilizing room air to support combustion
Preheated water	Water that has been tempered for inlet supply
Pressure Reducing Valve	A valve which automatically reduces inlet water pressure to a specified value at its outlet under static cold water conditions

Rated Storage Volume	Quantity of water (expressed in gallons) stored in a tank
Recovery (GPH)	The amount of water in gallons that can be heated in one hour
Residential	Water heaters for single family dwellings
Return Circulation System	Tempered water from or near the point of usage which eliminates waste of hot water used for long runs and adds storage to the system
RF	Recovery Factor - Rating based on the efficiency of the product which is input required to raise 1 gallon of water 1 degree F
	Gas - 75% to 85%		RF = 11 to 9.7 BTU/H
	Electric - 100%		RF = .0024 KW/H
	Oil - 70% to 85%		RF = 11.79 to 9.7 BTU/H

Safety shut off valve	A device on a gas appliance which shuts off the gas supply to the appliance to prevent a hazardous situation. A flame failure safety shut off operates when the actuating flame becomes extinguished. A 100% shut off cuts off all gas including main and pilot burners
Scale	A thin coating or layer, usually calcium on the bottom of a tank or interior parts, that may prevent heat transfer
Sealed Combustion	Sealing of combustion chamber to prevent spillage of combustion products
SEER	This is a measurement of the efficiency of cooling products. The U.S. Government's minimum efficiency level is 10 SEER for split systems and 9.7 for packaged units. The higher the SEER, the more efficient the cooling product. SEER stands for Seasonal Energy Efficiency Ratio.
Sediment (lime)	The substance that settles on the bottom of a tank
Series SYSTEM	Generally where the primary heater preheats water to a given desired general purpose temperature and feeds into another heater
Sliding Inner Door	A door slides along combustion chamber radius for easy access to the burner and pilot
Solenoid	A coil of wire in the form of a cylinder that when carries a current; resembles a bar magnet
Spark Ignition	Intermittent ignition device that utilizes a spark to light a flame
Split System	This describes an air conditioning or heat pump system that is split into two sections - an outdoor section and an indoor section. It won't work without the outdoor section plus an indoor section to move the air.
Spud	A threaded opening on the water heater tank
Stand By Loss	The amount of heat lost while unit is in stand by mode
Standing pilot	See pilot
Storage Tank	A tank used to hold a specific volume of water

T & P Valve	Temperature & Pressure Relief Valve - A safety device used to expel excess pressure or temperature from inside a tank
Tankless Water Heater	Commonly known as instantaneous
Temperature Rise	The number of degrees Fahrenheit (F) the incoming cold water must be raised to reach the desired hot water temperature
Therm	A measurement of 100,000 BTU's
Thermal Efficiency	Ability to transfer and absorb heat from fuel source into the water
Thermal Expansion	Water, a non-compressible liquid, expands when heated
Thermocouple	A small electric generator. Electron flow between the hot junction of 1200 degrees F and the cold junction of 600 degrees F creates millivoltage
Thermostat Lower	A device which automatically maintains a predetermined temperature in an appliance
Thermostat Upper	A device which automatically maintains a predetermined temperature in an appliance usually equipped with a safety shut off
Ton	You'll often see this as a measurement of the capacity of an air conditioning system. Don't panic, it doesn't measure weight! Just like gas and oil furnaces, air conditioners and heat pumps are rated in Btu's. One ton of air conditioning is 12,000 Btu's per hour. This means that a "one ton" air conditioning system has the capability of removing 12,000 Btu's of heat per hour from your home.

Usable Storage	The percentage of hot water that can be drawn from a tank before the temperature drops to a point that is no longer considered hot

Vacuum	Recommended for installation on all side (bottom) cold inlet heaters;
Relief Valve (anti-siphon)	prevents internal vacuum conditions that could drain a system by back siphonage, eliminates burned out electric elements and collapsed tanks
Venting Materials	Materials used for venting; i.e. PVC, CPVC, ABS, metal

Waterway Fitting	A channel through which water can flow; connects water heater to inlet & outlet lines
Water Hammer	A concussion or sound of concussion of moving water against the side of a containing pipe or vessel
Watt Density	Amount of watts concentrated per square inch of element blade surface area
Working Pressure	Maximum pressure of the operating system permissible

Yearly Cost	The cost of operating a water heater for a year

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