Plumbing and heating glossary
Plain-English definitions of the parts, systems and NYC rules you will hear a plumber mention. Each term links to the service page where it matters. New terms are added as we go.
42 terms. Last updated . Missing one? Ask us and we will add it.
A
- Anode rod
- A sacrificial metal rod inside a tank water heater that corrodes instead of the tank. Once it is used up, usually after 3 to 5 years, the tank itself starts to rust from the inside. Related: Hot water tank replacement
- Aquastat
- The temperature control on a hot water boiler that turns the burner on and off to hold the boiler water at a set temperature, and on many systems also controls the circulator. Related: Boiler repair
B
- Backflow preventer
- A valve assembly that stops water from flowing backward from a building into the public water supply. NYC requires annual testing by a certified tester on many commercial properties, including restaurants. Related: Restaurant plumbing
- Backwater valve
- A one-way valve on a building sewer line that closes when the city sewer surcharges, keeping sewage from backing up into the basement during heavy rain. Related: Sewer repair
- Boiler
- The appliance that heats water or makes steam for a building’s heating system. In NYC most residential boilers burn natural gas; some older buildings still burn oil. A boiler is not the same as a furnace, which heats air. Related: Boiler replacement
- BTU
- British thermal unit, the standard measure of heating output. Boilers and water heaters are rated in BTU per hour; a typical NYC row house boiler is in the 100,000 to 150,000 BTU range. Related: Boiler replacement
C
- Carbon monoxide (CO) alarm
- A detector for the odorless gas produced by incomplete combustion in boilers, furnaces and water heaters. NYC requires CO alarms in every home and apartment. Replace batteries twice a year and the unit when it reaches its printed end-of-life date. Related: Winter heating maintenance checklist
- Check valve
- A valve that lets water flow in one direction only. Used on circulator pumps, boiler feeds and sump discharge lines to stop backflow.
- Circulator pump
- The electric pump on a hot water heating system that moves heated water from the boiler through the radiators or baseboards and back. A failed circulator is a common cause of a boiler that runs but does not heat the house. Related: Boiler repair
- Combi boiler
- A wall-hung boiler that provides both space heating and on-demand domestic hot water from one unit, with no separate water heater. Common in smaller NYC homes and apartments where space is tight. Related: Boiler replacement
- Combustion analysis
- A test using an electronic analyzer at the flue to measure oxygen, carbon monoxide and flue temperature. It confirms the boiler is burning cleanly and venting safely, and is part of every proper annual service. Related: Maintenance plans
- Condensate neutralizer
- A cartridge of limestone media that raises the pH of the acidic condensate produced by a condensing boiler or water heater before it goes down the drain. The media is replaced periodically. Related: Boiler replacement
- Condensing boiler
- A high-efficiency boiler (typically 90 to 96 percent AFUE) that extracts extra heat by condensing water vapor out of its exhaust. It vents through plastic pipe out a side wall and produces condensate that must be drained. Related: Boiler replacement
D
- Dip tube
- The plastic tube inside a tank water heater that carries incoming cold water to the bottom of the tank. A broken dip tube mixes cold water at the top and causes lukewarm hot water. Related: Hot water tank replacement
- Direct vent
- A venting arrangement where the appliance draws combustion air from outside and exhausts outside through sealed pipes, rather than using room air and a chimney. Related: Tankless water heater
E
- Expansion tank
- A small tank with an air bladder that absorbs the increase in water volume when water is heated. Without one, pressure rises until the relief valve drips. Used on both hot water boilers and tank water heaters in NYC. Related: Expansion tank
F
- Flame sensor
- A rod in the burner flame of a modern gas boiler or water heater that proves the burner lit. A dirty flame sensor causes the appliance to light for a few seconds and shut down. Related: Boiler repair
- Flue
- The pipe or chimney passage that carries combustion exhaust from a boiler, furnace or water heater to the outdoors. Rust holes, loose joints or blockages let carbon monoxide into the building. Related: Boiler repair
G
- Grease interceptor
- A tank, under the sink or in the floor, that traps fats, oils and grease from a commercial kitchen before they reach the sewer. NYC DEP requires one in food service establishments and regular pumping by a licensed hauler. Related: Restaurant plumbing
H
- Heat exchanger
- The part of a boiler or water heater where the burner’s heat is transferred to the water. A cracked heat exchanger can leak water or combustion gases and almost always means replacement. Related: Boiler repair vs replacement
- Heat season
- In NYC, October 1 through May 31. During heat season landlords must keep apartments at 68°F from 6am to 10pm when it is below 55°F outside, and at 62°F overnight. Related: Nyc heat season landlord guide
- House trap
- A U-shaped trap on the main building drain, usually in the basement floor near the front wall, that keeps sewer gas out of the building. It is also the first place a main-line clog forms. Related: Sewer repair
- HPD
- The NYC Department of Housing Preservation and Development, the agency that enforces heat and hot water requirements in rental housing and issues violations and penalties. Related: Nyc heat season landlord guide
- Hydro-jetting
- Clearing a drain or sewer line with a high-pressure water hose that scours grease, scale and roots off the pipe wall. More thorough than snaking, which only punches a hole through the blockage. Related: Sewer repair
- Hydronic heating
- Any heating system that circulates hot water through pipes to radiators, baseboards or radiant floors. Most newer NYC boilers are hydronic; older buildings often have steam. Related: Boiler replacement
I
- Indirect water heater
- A storage tank with no burner of its own, heated by hot water from the boiler through a coil. It gives large volumes of hot water using the boiler’s efficiency and usually lasts longer than a standard tank. Related: Hot water tank replacement
L
- Low-water cutoff
- A safety control on a steam boiler (and many hot water boilers) that shuts off the burner if the water level drops too low. Float-type cutoffs must be flushed regularly during heat season. Related: Boiler repair
M
- Master plumber license
- The NYC Department of Buildings license required to perform and sign off on plumbing and gas work in New York City. Work on gas lines, boilers and water heaters must be done under a licensed master plumber. Related: About
- Mini split
- A ductless heating and cooling system with an outdoor compressor and one or more indoor wall units connected by refrigerant lines. In NYC, installation requires a DOB permit and often co-op, condo or Landmarks approval. Related: Ductless mini split
P
- Pigtail
- The small looped pipe under a steam boiler’s pressure control that keeps steam from reaching the control directly. It clogs with sediment and must be cleaned or replaced each season. Related: Boiler repair
- Pressure relief valve
- A spring-loaded safety valve on a boiler that opens to release water if pressure exceeds its rating, usually 30 psi on residential hot water boilers. A dripping relief valve usually points to a failed expansion tank. Related: Expansion tank
- Pressuretrol
- The pressure control on a steam boiler that cycles the burner to hold steam pressure, typically under 2 psi on a residential system. Related: Boiler repair
R
- Radiator air vent
- The small valve on a one-pipe steam radiator that lets air out as steam enters and closes when steam reaches it. A failed vent leaves the radiator cold or spitting water. Related: Troubleshooting
- Recovery rate
- How many gallons of water a water heater can heat by a given temperature rise in one hour. A higher recovery rate means a smaller tank can serve more people. Related: Water heater size guide
S
- Sediment
- Minerals and scale that settle at the bottom of a tank water heater. It causes rumbling, wastes fuel and shortens tank life. Flushing a few gallons each year removes it. Related: Hot water tank replacement
- Sight glass
- The vertical glass tube on a steam boiler that shows the water level inside. It should read about half full when the boiler is off and cool. Related: Boiler repair
- Steam boiler
- A boiler that boils water into steam, which rises through pipes to radiators and condenses back to water. Common in NYC buildings built before the 1950s. Steam systems run at very low pressure and need a low-water cutoff and working vents. Related: Boiler repair
T
- T&P valve
- The temperature and pressure relief valve on a tank water heater. It opens if the water gets too hot or the pressure too high. Test it once a year; replace it if it drips afterward. Related: Hot water tank replacement
- Tankless water heater
- A wall-mounted gas or electric unit that heats water only when a tap opens, with no storage tank. Needs an adequate gas line, proper venting and a yearly descaling flush. Related: Tankless water heater
- Thermocouple
- A small sensor in the pilot flame of an older gas boiler or water heater that keeps the gas valve open while the pilot is lit. A failed thermocouple means the pilot will not stay lit. Related: Boiler repair
W
- Water hammer
- The banging in pipes when water flow stops suddenly, or in steam systems when steam meets pooled condensate. In steam heating it usually means a pitch or venting problem, not a dangerous one. Related: Troubleshooting
Z
- Zone valve
- An electrically operated valve that opens to let heated water flow to one area, or zone, of a building when that zone’s thermostat calls for heat. Multi-family houses often have one per floor. Related: Boiler repair
See also the troubleshooting guide, the FAQ, and our guides for owners and landlords.
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