Hydronic Heating

Answering Questions for Pros on Hydronic Heating


Q. What is hydronic heating?
A. Hydronic heating systems use a boiler to heat water that is used as the heat transfer medium. The heated water or steam is then circulated to heat distributors located throughout the home. These heat distributors can be radiators, finned tube baseboard, radiant tubing, towel warmers, and kick-space heaters. The boiler also can be used to indirectly heat domestic water and whirlpool baths and can be used for ice and snow melting on sidewalks and driveways.

Q. Why is consumer interest in hydronic heating rapidly growing?
A. Homeowners are demanding comfortable and efficient heating for their homes. Hydronic heating provides draft-free, quiet, and environmentally clean heat with no hot or cold spots. Furthermore, hydronic heating allows each room or area of the home to be zoned separately. Hydronic heating is also energy efficient because it is delivered through completely sealed heat distribution systems with minimal loss of heat.

Q. What is the advantage in using plastic tubing in hydronic installations?
A. The advantage for both the installer and the homeowner is that plastic tubing is easy to install. Tubing is small and flexible, so it can quickly snake between walls, above ceilings and under floors to the heating distribution points throughout the house. The placement of tubing can be done at the same time the boiler is being installed, making the entire job more speedy and efficient. Only plastic tubing designed and rated for heating applications should be used for hydronic installations.

Q. How do I get training for installing hydronic equipment?
A. Click here for educational opportunities for hydronic equipment installers, including installation of baseboard, radiator, and radiant heating systems.

Q. Where do I find out how to service a specific piece of hydronic equipment?
A. For servicing specific hydronic equipment, contact the manufacturer directly. Click here for hydronic equipment manufacturers that are members of AHRI.

Q. How can a customer with tile floors in the bathroom and kitchen have warm floors in winter?
A. Radiant heating warms floors in the bathroom, kitchen, and throughout a home. This form of hydronic heating sends warm water through extremely durable tubing that is installed in or underneath floors, as well as in walls and ceilings.

Q. How does radiant heating work?
A. Radiant heating systems circulate warm water through tubing that is installed in floors, walls, or ceilings. This form of hydronic heating warms people and objects, and not air. Heat flows through the room gently and completely without breezes, hot spots, or cold spots.
Image removed. Radiant heating systems circulate warm water through tubing that is installed in floors, walls, or ceilings.

Q. What is a “radiant-ready” house?
A. The most economical time to include radiant heating is when the house is being built. Many builders today install radiant tubing in the floors, sidewalks, and driveways of homes they are building even if the home buyer does not ask that the radiant heating be hooked up. This makes it a simple and cost-effective matter to switch to the radiant heating system whenever the homeowner wishes.

Q. Can hydronic heating be used outside the house?
A. Yes. Hydronic heating can be used to heat swimming pools and whirlpool spas by use of a boiler or pool heater and a heat exchanger. In addition, durable tubing also can be installed in sidewalks and driveways to melt snow and ice.

Q. How can air conditioning be used in a hydronically-heated home?
A. There are several air conditioning (AC) systems that work well with Hydronic Heating:

High Velocity Mini Duct System: This system transfers air to small (2" inner diameter), round outlets in each room of the home through flexible tubing that weaves in between spaces in the walls, ceilings or floors. Installation is easy, economical, and nearly unobtrusive.
Split-System Central Air Conditioner: In this system, a condensing unit is installed outside the home and a matching indoor air handler unit or furnace with coil is inside the home. Ductwork transfers the cooled air throughout the home.
Separate Standard Air Conditioning System: Many homeowners choose to install a separate AC system along with their Hydronic Heating system. In a typical installation, a rooftop AC unit sends cool air to the home through small flexible tubing (similar to a High-Velocity AC System), and is distributed by small vents in the ceilings of each room of the home.

Q. How do high-efficiency condensing boilers work?
A. Condensing boilers achieve high efficiency by capturing and using heat from the combustion process that would otherwise be wasted. The boiler’s heat exchanger uses the exhaust gases from the combustion process to preheat water as it enters the boiler. In addition, the water vapor produced in the combustion process condenses back into water and also releases heat that is then re-used. Together, these two processes create the high efficiencies associated with condensing boilers. Just as important as the efficiency of the condensing boiler is the efficiency and proper installation of the overall heating system to which the boiler is a component. To achieve maximum efficiency, a total heating system approach is required.

Q. What are the advantages of acquiring NATE Certification?
A. North American Technician Excellence, Inc. (NATE) is the leading certification program for technicians in the heating, ventilation, air conditioning, and refrigeration (HVAC/R) industry and is the only testing process supported by the entire industry. According to NATE, a recent survey from Service Roundtable shows that NATE-certified technicians have fewer callbacks than technicians who aren’t NATE-certified. In addition, when on a warranty call, their expenses are about 30% lower than non-certified technicians — and their billing efficiency is also higher than technicians who are not NATE-certified. For details about NATE Certification.

Q. Where do I find the sizing specifications for hydronic equipment?
A. Sizing specifications are available on Hydronic equipment manufacturers’ websites.

Q. For what types and sizes of buildings is hydronic heating best suited?
A. Hydronic heating is appropriate for any residential home or building. For larger homes, two smaller boilers may be used in sequence, with the second boiler only operating when it is needed. Larger buildings, such as schools and hospitals, may install multiple boilers operating in sequence.

Q. Can hydronic heating be used in a home that also has other types of heating systems?
A. Yes. There are hydronic heating solutions for converting or supplementing existing warm air, heat pump, and solar systems.


    Major Home Renovation Includes Radiant Addition

    The owners of a 2,400 square-foot home dating back to the Revolutionary War were planning their first-ever major renovation. As part of several other remodeling projects, the old hydronic system required updating. In addition to upgrading the mechanical system, the owners also favored adding radiant heat to the home.

    After conducting research, the homeowners and an HVAC company chose a compact, high-efficiency boiler to replace the old, large boiler in the basement and installed an indirect-fired water heater to meet the family’s hot water needs.

    The kitchen also was a focal point of the renovation. The room was only heated by a standing radiator and the floors in the room were ice cold during the winter months.

    To determine each room’s need for tubing and proper water temperature, the installer utilized heat loss calculation and design software based on a design-day temperature of zero degrees. This program factored in information on building specifications and construction materials. With configurations complete, radiant heating panels and tubing were then installed under the flooring.

    The new system provides highly-efficient heat for the entire house, even during severe winters, and delivers plenty of hot water for showers, baths and laundry while consuming much less energy than the prior system.

    Condo Complex Conserves Costs with Hydronic Radiators

    The builders of a new 12-unit condominium complex in Brooklyn, N.Y., sought a quality heating installation, but also wanted to keep construction costs low. The builders were familiar with the benefits of hydronic heating and selected a mechanical firm with expertise in such installations.

    Each condo unit closet was fitted with a wall-mounted modulating condensing combi-boiler with PEX tubing running within the walls and to the cast-iron radiators. A two-zone system was created and radiators were placed under windows, in hallways and in each bathroom.

    And how do the Brooklyn condo owners like the hydronic heating system? Residents report that the heating system is comfortable at all times and barely noticeable. In addition, owners save money on energy bills due to the unit’s high efficiency.

    Church Turns to Condensing Boilers

    A church in Chicago decided to undergo a mechanical system overhaul to increase energy savings and heating system inefficiencies in both the east and west locations of the facility.

    After careful consideration, the church installed high efficiency condensing boilers. In addition, the series piping was converted to primary secondary piping, which reduces energy loss of system water running through a boiler that is not firing.

    Based on new condensing efficiency levels, the church received rebates from the gas company, ultimately saving both fuel and money.

    Upgrading Elementary School Boiler Efficiency

    A large elementary school in Marlborough, Mass., sought to improve efficiency and lower operating costs.

    Working with an HVAC company, the school decided to install four high efficiency commercial boilers and an indirect fired water heart for domestic hot water. The entire boiler room was gutted and new venting was installed.

    The school runs the boilers in parallel, and they maintain optimum conditions even on the coldest days of winter. By balancing the fluctuating load requirements over multiple boilers, the units can now operate at the maximum peak efficiency.

    Major Snow Melting System Handles Midwest Winters

    A major trucking company wanted to install an extensive, 22,000 square-foot snow and ice melt system outside its new headquarters in a Midwestern city to make it safer for employees and visitors to navigate around the complex during winter.

    Installing the system required a team of technicians who embedded 32,000 linear feet of radiant tubing in concrete around the building. The tubing carries a heated 50/50 glycol solution to and from a large plate-to-plate heat exchanger connected to a steel tube boiler.

    The 11-zone hydronic system has a liquid volume of almost 1,000 gallons and requires 175 gallons per minute to accomplish the mission of melting snow and ice before such slippery conditions have time to accumulate. During winter snowfall, the system heats the hard surfaces up to 35°F, sufficient to keep surfaces clear.

    With the hydronic system in place, employees and visitors can more easily navigate the facility’s large circular driveway, sidewalks, and entryway.

    Applying new technologies to a 2,000 year-old heating method is revolutionizing the way one thinks about home and business comfort. Hydronic heating continues to grow in popularity due to its excellent indoor comfort, lower energy costs, and improved indoor air quality. Today’s hydronic systems are being used in conjunction with forced air systems or as a standalone home heating system. Let’s review some of the latest innovations.

    Growth of Radiant Floor Heating

    Homeowners continue to migrate away from carpeting to hard floor surfaces such as wood, tiles and stones. Along with this transition has come a desire to enjoy warm floors. This wish has forged the growth of the radiant floor heat market in the U.S., and it continues to expand on an annual basis as hard floor surfaces grow in popularity.

    New Energy Efficient Boilers

    Energy-efficient condensing boilers appeared in the U.S. market at the end of the 1990s and their sales have grown almost every year since. Reasons for the switch from non-condensing boilers include increasing energy prices and more awareness of energy efficient products, plus the growing number of governmental policies and incentive programs.

    Since September 2012, the residential boiler minimum efficiency requirement or annual fuel utilization efficiency (AFUE) in the U.S. is 82% for gas hot water and 84% for oil hot water boilers. Some jurisdictions in the U.S. have building or energy codes that require the reporting of the efficiency ratings of boilers and other heating products.

    Condensing gas wall hung boilers also are seeing increased sales growth as they are compact and fit into smaller spaces. These wall hung units are ideal for hydronic under floor heating when utility space is minimal.

    Use of Combination Boilers

    Combination (or combi) boilers represent one of the latest innovations in hydronic heating technology. A combination boiler combines a boiler and a water heater to provide space heating and domestic hot water heating in one compact, efficient device. These boilers are a popular option for many households, especially where there is limited space for heating equipment.

    Most combination boilers on the market today utilize a small heat exchanger built into the boiler to produce domestic hot water. A high efficiency combi boiler often has an AFUE of 92%–95%, offering abundant hot water in a compact, reliable appliance.

    Due to its energy efficient and eco-friendly design, a combi boiler offers considerable cost and space savings. Combination boilers are the fastest growing boiler in the industry with many manufacturers reporting as much as 12%–13% growth per year in the sale of these new units.

    Boiler Material Design

    Stainless steel remains the most dominant heat exchanger material for condensing boilers in North America and is used by virtually all manufacturers. However, aluminum condensing boilers are growing in popularity in the U.S. Copper is more prevalent in commercial boilers. Cast iron is marketed as very reliable, requiring low maintenance and lasting the longest. Heat exchangers for oil and dual fuel boilers are mostly made of cast iron.

    Eco-friendly Installations

    Boilers can be installed in combination with other non-traditional eco-friendly heating systems. A solar water heater can increase the energy efficiency of the system and work in tandem with a boiler.

    Geothermal heat pumps use the natural warmth of the ground several feet below the soil to preheat water. This method can reduce the amount of natural gas, electricity, or oil that a boiler uses to save energy.

    The Future of Hydronic Heating

    The future of hydronic heating likely will focus on low water temperatures, which improve the efficiency and performance of modern heat sources like modulating/condensing boilers, solar thermal collectors, and heat pumps. With proper design one can create a system that requires supply water temperatures no higher than 120°F under design load conditions.

    Future sizing for radiant panels, panel radiators, or even baseboard radiators could consist of supply water temperatures no higher than 120°F at design load conditions. Even lower water temperatures are possible with some heat emitters, including extended surface baseboard and micro-fan-enhanced panel radiators, which can be sized to deliver design load output using supply water temperatures as low as 95°F.

    Low water temperatures also can be combined with low-mass heat emitters. One issue with radiant floor heating is that its response to temperature swings is slow. To prevent unacceptable temperature swings, it is necessary to quickly stop heat emission when the desired comfort condition is achieved.

    The lower the water content and weight of the heat emitter, the more quickly it will be able to respond. Low-mass heat emitters will react much faster to temperature changes and reduce temperature fluctuations. Operating at lower temperatures makes low mass units a perfect match for condensing boilers.

    In addition, with low mass heat emitters, fin tube elements are spaced closer together and corrugated to create larger surface area. Low mass emitters also take up less space, provide more output and increased safety for building occupants due to lower surface temperatures.

    You are hearing more and more about hydronic heating and you would like to know more about it. So how does a builder or remodeler get started? Here are some sound guidelines that many builders and remodelers have successfully followed to educate themselves in the use of high-quality, high-comfort hydronic heating.

    • Research manufacturers of hydronic heating equipment. Conduct online research and visit the websites of reputable manufacturers of hydronic equipment. Many have training programs specifically geared to the needs of builders and installers. For a list of manufacturers visit the Hydronics Institute resources section of the AHRI websit.e
    • Learn about hydronic installation advantages and requirements. There are a number of industry organizations that provide outstanding basic and advanced training on the latest system design and installation techniques for hydronic installations. The specialized insights and methods you learn here can be invaluable to help you better select the right hydronic installer, and to knowledgeably manage your hydronic installations. For more information on training programs visit Radiant Professionals Alliance's RPA University and Oilheat America.
    • Visit with hydronics professionals at the Hydronic Industry Alliance booth at industry trade shows. When you’re at industry trade shows such as the International Builder’s Show, AHR Expo, or others, be sure to stop by the Hydronics Industry Alliance booth. Attend the training seminars and speak with HIA members. These experts can answer questions and give practical information. They also will steer you to other industry professionals who can help you learn more about hydronic heating. To find out more about industry shows visit the Hydronics Industry Alliance website.
    • Talk with other builders and remodelers in person or online. Whenever you can, have a chat with professionals who work with hydronic heating every day. Make person-to-person conversations part of your hydronics education. There is also an online forum for hydronic heating professionals and homeowners at HeatingHelp.com.
    • See hydronically heated homes for yourself. At every opportunity, visit a home that has Hydronic Heating. Talk with the homeowner and find out what it’s like to live with hydronic heating. Ask for ideas on how their system might be improved during their next installation.


    Builders and remodelers sometimes believe hydronic heating is an expensive option; however the price of all systems vary depending on the installation process.

    Radiant heating systems offer savings from lower fuel costs, versatile design options, and reduced maintenance over the life of the product.

    Hydronic Heating Saves Energy

    Hydronic heating utilizes water, one of nature’s most efficient conductors of heat. Heated water in a boiler stays hot for a long time — long after the boiler stops firing. This warm water is circulated around the house and continues to heat the home. The homeowner pays once to warm the water, but the water keeps on transferring this heat.

    In addition, hydronic heating has little effect on the air pressure in the heated space. The air pressure remains stable in the room, and the heat stays where it is needed — another energy saver.

    Perhaps the most compelling reason for hydronic heating’s efficiency is its ability to provide zoned heating. This option can be a key selling point for prospective home buyers. Buyers today crave energy efficient solutions and hearing how they can heat one room or a few rooms where they spend most of their time, while lowering the temperature in other rooms, can be a major selling point.

    Versatile Design Cuts Costs

    For home builders, a primary advantage of hydronic heating is that it is inherently multi-purpose. The same boiler used for home heating also can provide domestic hot water, pool and spa heating, sidewalk and driveway snow melting, and even towel rack warming. This eliminates the need to install entire separate systems for these additional uses. Also, having these extra heating luxuries can help differentiate a home from others on the market.

    A hydronic installation also enables the builder to use different types of hydronic heating delivery systems in separate areas of the home. It is not uncommon for a home to have radiant floor heating on the first floor and finned tube baseboard or panel radiators for heating the second or even the third floors. Again, the same boiler provides the hot water for all of this heating, no matter how the heat is delivered.

    Easy Installation

    Installing a hydronic heating system is surprisingly fast and easy. Hot water is circulated throughout a house via copper or small, flexible, PEX tubing (extremely durable tubing manufactured from polyethylene plastic). This tubing is easy to install, requires very little maintenance and it saves time, money, and headaches.

    Long Life

    The average life expectancy of a boiler system can be as long as 30–45 years.