Omnia Mechanical Group

571 Timpson Place Bronx, NY 10455

Phone: 212-534-2500

Contact us on email!

Boiler Terminology for Property Owners and Managers

With the return of heat season to New York City, we thought it might be helpful to provide a review of industrial boiler terminology for our clients with apartment buildings and commercial rentals. When you meet with experts like the service technicians at Calray Boilers, you will better understand any problems or repairs to your boiler system. This list is by no means comprehensive – there are literally hundreds of words used in boiler technology – but this is the most common nomenclature we use in our day-to-day work.

Industrial Boiler Terminology

Air preheater (APH)

This warms air that is used with fuel as part of the combustion process in the burner area of the boiler, removing moisture and making combustion faster and more efficient.


Aquastats are components that send signals to the burner to fire or stop firing, based on the temperature of water in the boiler tank.


A baffle is a barrier that restricts the flow of fluid to create turbulence and increase the rate of heat transfer.


This is the process of removing impure water with too many total dissolved salts (TDS).


Short for British thermal units, a BTU is the amount of energy needed to raise a pound of water one degree Fahrenheit. Here’s a handy table with some conversions of heat and heat capacity involving BTUs.

1,000 BTU = 1 lb. of steam
150 BTU = 1 sq. ft. of hot water
34.5 lbs. steam/hour = 1 boiler horsepower
1 boiler horsepower = 140 sq. ft. of steam radiation
240 BTU = 1 sq. ft. of steam
34,500 BTU = 1 boiler horsepower
1 gallon #2 oil = 140,000 BTU
1 cubic ft. LP gas = 2,550 BTU
1 cubic ft. natural gas = 1,000 BTU
1 kilowatt hour = 3,413 BTU
1 therm. natural gas = 100,000 BTU


This is where fuel, such as oil or gas, is combusted to heat water in the boiler tank.

Check valve

A check valve is a specific type of valve that allows fluid flow in only one direction – usually used to prevent backflow to parts like the boiler feeder.

Circulator pump

The circulator pump pushes water out of the boiler to distribution lines for kitchen taps, showers, laundry, and the like or to radiators.


Combustion is an energy conversion process that involves the burning of a hydrocarbon (oil, gas, wood, etc.) in the presence of heat and excess oxygen. In a boiler, this occurs in the combustion chamber (aka firebox) where the burner is located.


This is radiator steam that has cooled (condensed) and returned to its liquid form as warm water, to be returned to the boiler for reheating via the condensate return system.

Expansion tank

An expansion tank is a safety tank that can absorb excess pressure from the main boiler tank to prevent dangerous pressure buildups.

Exhaust stack

This is the chimney or flue that conducts combustion byproducts, like carbon monoxide, out of the boiler system and out of the building.


Feedwater is the fresh water that is supplied to the boiler, usually via an automatic water feeder with need detected by a sensor.

Feedwater line

This is a pipe that conducts feedwater into the boiler tank with the help of a boiler feeder pump that’s triggered automatically.

Flue gases

These are gases created after combustion, including carbon monoxide, carbon dioxide, sulfur dioxide, and water vapor.


Used to prevent leaks at joints, boiler gaskets are often made of steel. Other types of leak prevention in the system, including in pumps, are seals and O-rings.

Hartford loop

A Hartford loop is a safety piping arrangement still in use from the early 20th century to facilitate condensate re-entering the boiler more efficiently.

Heat capacity

This is the amount of heat that a fluid can store, typically expressed as kilocalories/kilogram/degree Celsius or joules/gram/Kelvin.

Heat exchanger

Heat exchangers are elements of the boiler system that transfer heat created by combustion to the water in the boiler tank. Heat exchangers are usually made of sturdy metal, like copper, cast iron, or steel.


A manometer is a device that measures boiler pressure at various points in the system in relation to atmospheric pressure.

Pressure reducing valve

Required by law, this valve is a safety addition to release steam pressure that could otherwise become dangerous.

Return lines

Return lines, sometimes also called steam traps, bring condensed steam back from radiators in the form of warm water to be reheated and used again. This is much more efficient than heating fresh water from the boiler feeder and extends the life of the boiler as well as saves on fuel costs.

Supply lines

These are the lines that distribute water from the boiler to places where it’s needed, like hot water taps and radiators.

Total dissolved salts

Total dissolved salts, or TDS, is the amount of other chemical components in boiler water, important to analyze to prevent clogged pipes and valves, tank mineral scale buildup, and corrosion.

Working pressure

This is the pressure at which a boiler normally works, carefully adjusted for optimum performance within a safe range.

Call Calray Boilers for Your Seasonal Maintenance Check

New York City’s hyper-local, blue-chip experts

While we recommend regularly evaluating your boiler for problems and making sure all your safety equipment works properly, it’s no substitute for regular professional service. Having your boiler system checked over once or twice per year will lengthen its lifespan, save you money on fuel and water, and reduce the number of hassles you experience due to boiler malfunction.

Don’t wait until your boiler is running at peak levels this winter to find out you need parts repaired or replaced. We recommend an autumn service call to get it in tip-top condition and give you peace of mind heading into those wintertime subzero temperatures.

Call Calray Boilers today at 212-722-5506 or reach out online at your convenience to schedule an appointment via our website.

Our Privacy Policy

Omnia Mechanical Group(the “Company”) strives to ensure the highest standards for property listings and customer information privacy. Please review the following statement to learn about our company practices and policies. Please be aware that our Privacy Policy is subject to change at any time.

1. Purpose.

This Privacy Policy (“the Policy”) provides information on how the Company uses your personal information. By agreeing to the Policy, you agree to our collection and use of your personal information as described in the Policy. This Privacy Policy is effective for all new users of

2. Personal Information.

You can browse some areas of (“the Website”) without being a registered user. However, certain activities do require registration. (You consent to the transfer and storage of your information by registering with

3. Use of Information.

Our primary purpose in collecting personal information is to provide you with a safe and user-friendly experience. For example, the Company may use your personal information to:

  • Improve our services and the Website’s content and layout;
  • Provide the services and necessary customer support you request;
  • Resolve disputes, collect fees, and troubleshoot problems;
  • Track and record customer satisfaction with our services;
  • Protect the Company against error and fraud;
  • Inform you of special promotions and announcements;
  • Enforce our agreements, terms, conditions, and policies; and
  • As otherwise described to you at the time of collection.

We may occasionally ask you to complete optional surveys. These surveys are used to improve and customize your experience with

The Company always provides you the ability to opt-out of further communication such as promotions and surveys; see the Opt-Out section below.

The Company does not share any of your personal information with outside organizations, companies, individuals, etc. The only exception to this standard is if such a disclosure is reasonably necessary to respond to any and all legal processes.

4. Links to Other Sites.

The Website may have links to other websites that may collect personally identifiable information about you. The Company is not responsible for the privacy practices of the content of those linked websites.

5. Safety & Security Precautions.

The Website has strict security measures in place to protect you and your information from fraud. Once your information is provided to Omnia Mechanical Group, we strive to ensure the confidentiality of your identity and information.

6. Opt-Out.

The Company provides you with the opportunity to opt-out of receiving promotional and other non-essential, marketing-related communications from Omnia Mechanical Group. If you would like to opt-out of these select communications, please see any of the Company’s email communications and follow the directions indicated.

7. Account Protection.

Your password ensures the security of your account. When choosing a password, the Company suggests using various characters. It is highly recommended that you do not disclose your password to anyone. (If you do disclose your password or your personal information with others, you are responsible for all actions taken in the name of your account.) If the security of your password is compromised for any reason, please contact the Company immediately.

8. Accuracy of Information

The Company does not guarantee the accuracy of information for any and all of its properties on the Website, and is not responsible for any errors or misrepresentations (made by Renters, the Client, or otherwise).

9. Cookies

The Company may place a small cookie on your computer’s hard drive. This allows us to personalize your use on the Website. In order to maximize the functionality and usability of the Website, you must set your browser’s preferences to allow both permanent and temporary cookies.

10. Changing Your Personal Information.

Should your personal information change, please immediately update your information on the Website. This will ensure the accuracy of our records. The Company does retain personal information from closed accounts in order to comply with law and collect and disburse any fees owed.

11. Third Parties

This Privacy Policy addresses only the use of information we collect from you. Since does not control the privacy policies of third parties, you are subject to the privacy policies of those third parties. It is advisable that you consult with the management of third parties before you disclose your personal information to others.

12. General

We may amend this Privacy Policy at any time by posting the amended terms on the Website. All amended terms are immediately effective after they are initially posted on the Website.

13. Privacy Policy Questions & Concerns

Questions and/or concerns regarding the Policy should be emailed to the following email address: