What Is Hydronic Heating System? Design & Components

Have you ever walked into a room that has the right temperature but you couldn’t spot any vent or heat pump and wondered what’s the secret? It is a hydronic heating system.

Well, the concept of hydronic heating is not something new. People have been using it for hundreds of years. The first known central heating system can be traced back to 2,500 BC. Greeks in ancient Rome developed a radiant heating system called hypocaust that heated empty spaces under floors.

Hydronic heating/cooling system has come a long way since then. Today, several major cities have a district heating system that provides publicly available hot/cold water through underground piping. Residential buildings and offices often use these services to maintain indoor temperatures.

We now have different types of heating systems available in the market. The best solution depends on various factors, such as energy efficiency, the level of comfort you desire, and the type of flooring used in the home. Another major factor is your location and how long and cold are the winters in your region.

In this article, we will only focus on the hydronic heating system. We will cover how it works, what are the different components involved in hydronic heating, what are its benefits, and how much would it cost to install it in your home. Let’s start with the very basic question.

What Exactly is Hydronic Heating System?

Hydronic heating systems use liquid water or water solution (usually glycol with water) to heat your home. They consist of a heat source and a network of pipes that transport the hot water to different parts of your home.

It can be as simple as a water heater connected to a loop of pipes that warms the floor. A complex hydronic system may use multiple boilers working in stages and releasing their heat through various heat emitters such as panel radiators, radiant ceiling panels, and fin-tube baseboards.

Modern hydronic systems are equipped with thermostats to direct certain temperatures to different rooms. They may also be programmed to switch on/off at particular intervals. Unlike other heating solutions, such as furnaces, hydronic systems distribute heat evenly throughout the room without affecting the humidity levels.

Moreover, they can be used as radiant wall and floor heating systems, hydronic towel warmers, hydronic baseboard heaters, snow-melting systems, and pool-heating systems.

How Does It Work?

A hydronic system heats the water in a boiler and distributes it across the home through piping in the walls and floors. The hot water then travels into radiators that are installed in every room. These radiators then transfer the heat to their surroundings. The water also travels through the piping under concrete slabs, transferring heat to the whole surface area of the floor.

Unlike other heating solutions that use vents or fans to blow warm air, hydronic heating systems heat the room through thermal radiation. And since water is a good conductor of heat, these systems are both effective and energy-efficient.

The boilers may be powered by different energy sources, such as electricity, gas, or biofuels. The ones with low water content are quite efficient. It doesn’t matter where you live or how your home is constructed, you can always find a heating source suitable for your house.

There are also many different types of radiators. They are nothing but passive heat exchange devices that transfer thermal energy from one medium to another for the purpose of heating or cooling. They transfer heat (from hot water) in the form of electromagnetic radiation waves.

While radiators come in different sizes, their typical dimension is 2 feet * 8 feet. For effective results, they are placed one to two inches from the wall.

Modern hydronic systems are precise and can be configured in many ways. They may include one or more underfloor coils, wall-mounted radiators, and heated towel rails. Each configuration is capable of matching the exact requirements of the customer. 

Furthermore, when the space is radiantly heated, comfort can be maintained at lower air temperatures. This results in further energy savings.

Different Components Of Hydronic Heating System

While there are many different types of hydronic heating devices, they all have a few common components:

Heat Source

The most common heat source is a boiler, which is usually installed in the basement or back of the building. It uses gas (gas-fired boiler), electric (electric boiler), oil (oil-fired boiler), or a mixture of them to heat water. Based on your settings, it can heat the water from 33°C (90°F) to 94°C (201°F).

Common types of boilers include steel boilers, cooper water-tube boilers, and cast-iron boilers. Steel boilers, in particular, are inexpensive, readily available, and can be easily formed or welded to the desired shape. They also don’t corrode or react with oxygen (under normal circumstances) and provide satisfactory service for several years.

Another emerging heat source is the geothermal heat pump. It transfers heat stored in the earth or in groundwater into a home. It is far more energy-efficient than furnaces, boilers, and electric heaters.

Centrifugal Pumps 

Centrifugal pumps (also called circulators) transport fluids from a heat source to radiators installed in different rooms. It does so by converting rotational kinetic energy into hydrodynamic energy of the fluid flow. This rotational energy comes from an electric motor or engine.

Modern pumps are integrated with Variable Frequency Drives (VFDs) to dynamically adjust flow or pressure as per the system requirements. Advanced pumps have in-built overload protection against extreme voltage and dry run, BMS options, and data logging capabilities. Plus, they have proved to decrease power consumption by up to 80 percent.

Expansion Tank

Expansion tanks are essential in closed-loop heating systems. They absorb the expanding fluid, keeping the pressure within permissible limits at all points of the system.

In other words, an expansion tank of a suitable size accommodates the expansion of water during the heating and cooling cycle without allowing the machine to exceed the maximum pressure limits. It uses compressed air to accept and expel the changing volume of fluid as it heats and cools. Most tanks come with a bladder or diaphragm to isolate the expanded fluid from the pressure-controlling air cushion.

Air Separator

When water is heated, it produces air bubbles, which can lead to corrosion in heating systems. These bubbles also decrease the heat permeability, which ultimately results in less efficiency. To stop these air bubbles from forming, all heating systems are equipped with an air separator.

The air separator removes dissolved gases or microbubbles from the closed or open heating system. It collects and puts out the bubbles on the surface of a specially built metal filter. During the process, it also isolates undissolved impurities and minimizes the chances of air lock.

Vent Valves 

The air circulating in the pipes can create issues like corrosion and cavitation. Vent valves automatically remove the trapped air that prevents the free movement of water. They are installed in the radiators, baseboards, convectors, and high points in piping systems.

Limit Switch 

A high-temperature limit switch is a safety device that has two functions in the boiler’s operations: it turns the boiler (or other heating sources) on and off during the normal heating cycles, and it senses heat and shuts down the entire system if the interior temperature gets too high.

Types

Based on terminals (or heat emitters), hydronic systems can be categorized into several types. Different terminals can be integrated into a single heating system to fulfill the requirements of a large home.

Cast Iron Radiators

These are one of the oldest types of radiators still in use today. They are reliable, highly durable, and offer long-lasting heat. The iron remains warm much longer than radiators made of other conductive metals such as aluminum. But since they are large and heavy, they are not usually mounted on walls.

In-Floor Radiant

In hydronic radiant floor systems, heated fluid is pumped from a boiler through a loop of flexible tubing embedded in the floor. As the thermal waves rise from below, they warm up every object they strike without leaving any uncomfortable hot or cold spot. While these systems are quite expensive to install, their long-term running cost is low compared to electric radiant floor heating systems.

Fin Tube Baseboard

Fin Tube baseboard contains copper tubes with aluminum fins. The aluminum fins are mechanically attached to the copper tube to transfer the maximum amount of heat. The baseband is built with various enclosure styles to meet any architectural style and application.

Cast Iron Baseboard

Cast iron baseboard is less susceptible to the noises associated with the contraction and expansion of other baseboards. It is designed for quiet operation, high efficiency, and uniform heat distribution. Available in several different lengths, these baseboards can easily blend with any decor and can be painted to match your room’s color scheme.

Panel Radiators

A panel radiator looks like a flat surface that transfers convective and radiant energy (heat) to an indoor space. Longer panels have more surface area to emit heat. Some panel radiators have convertor fins. These fins are zig-zag metal strips attached to the back of the single panel radiator or in the middle of the dual panel radiator. They further increase the radiator’s surface area and thus its heating capacity.

Unlike cast iron radiators, panel radiators are slim and lightweight. They have a modern, stylish design and are usually hung on the wall.

Benefits

These heating systems have more advantages than people realize:

More Comfort 

Hydronic systems distribute heat evenly across the room, avoiding uncomfortable hot spots and foul smells. They not only maintain the desired air temperature in every room but also warm objects as well as room surfaces. Superior comfort is the biggest reason people prefer these systems over forced-air heating systems.

Good for Health 

Unlike warm-air heating devices that operate with a blower, hydronic heaters transfer heat through radiation (just like heat from the Sun). They don’t circulate airborne contaminants, dust particles, and allergens around homes. Also, air heating solutions dry out the air which affects our eyes, skin, sinuses, and throats. That’s not the case with hydronic systems.

Efficient

It requires less energy to heat the water and transport the heat throughout your home. Water is a good conductor of heat and can retain heat for a longer time than air. Warm air, on the other hand, can lose energy or leak through joints or gaps as it travels through ducts.

Hydronic heating is very effective for rooms with high ceilings. Since it evenly distributes heat, you can keep your room at lower temperatures while still feeling warm. This further reduces energy consumption.

Modern hydronic systems can reduce your heating bills by up to 35% as compared to other heating solutions. A small portion of that savings comes from not having to switch on/off the furnace all day to maintain a stable (comfortable) temperature.

Quiet

Hydronic devices are so quiet that you will often forget you have them installed in your home. Unlike blowers that sometimes make squeaking or screeching noises, radiant heat systems are completely silent. Also, you don’t hear the rush of air that heating vents push out.

Safer and Durable 

Hydronic systems have less critical components or electrical connections for fire hazards. And since they have fewer moving parts they are more durable. A cast-iron hydronic system, for example, can easily last 20 years or more with little maintenance. While there are always possibilities of electric failure or pipes bursting, the chances of that happening are very low.

Allow For More Versatile Installation  

Homeowners can install and customize the hydronic system as per their needs. There is a wide range of boilers available in the market that works with every fuel source. Unlike conventional systems that require massive ductwork and air systems with big chases, Hydronics pipes can be easily installed in the walls and routed across the home.

The heating source can be connected to various types of heat emitters, offering countless possibilities to accommodate comfort needs, budget constraints, and aesthetic tastes. Because of these advantages, hydronic heating solutions are widely used in offices, hospitals, airports, schools, universities, and several public- and commercial buildings.

Installation

There are several different methods to install a hydronic system. Whether you are renovating your home or building a structure from the ground up, these heating systems can be installed in all scenarios.

If you are planning on using radiant flooring, there are two methods to install it.

1. Dry Installation

It involves using prebuilt panels that have been fabricated with tracks for the radiant tubing. The pipes can be easily looped through the tracks before putting a floor cover over the top. This is a great option if you are not planning to pour concrete into a slab.

But since there is no concrete over the top, you need to put an insulating material and heat reflector to ensure the proper distribution of heat.

2. Wet Installation 

As the name suggests, wet installation involves placing the radiant pipes into the concrete when it is being poured (or before it has been poured). Once the concrete dries, it protects the pipes from damage while also providing a thermal mass to absorb heat and radiate it evenly throughout the home.

For slab on grade foundations, the pipes are connected to the reinforcing structure within the slab before pouring the web concrete. For thin slab installations, the pipes are connected to the subfloor and a layer of self-leveling concrete is poured over the top. This increases the floor height up to 4 centimeters.

Installing Wall Radiators 

The radiators and baseboard heaters are easier to install; it requires fewer pipes and there are no concerns about concrete. Pipes can be installed within a wall and then well-insulated to mitigate heat loss. These pipes connect the boilers (usually placed in the basement) with different types of heat emitters installed in each room.

The big plus point of installing a hydronic heating system is doesn’t require drilling, sawing, or removing major pieces of the home that could weaken the structure.

Since water is about 3,400 times more thermally concentrated than air, a hydronic machine has to move only 1/3400 of the volume of water to provide the same amount of heat as a forced-air system. This means you can replace a big cumbersome ducting with small tubing.

More specifically, a 3/4 inch thick pipe can transfer the same amount of heat as an 8*14 inch duct when both hydronic and forced-air heating systems are operated in similar scenarios.

Frequently Asked Questions

How much does it cost to install a hydronic heating system?

While the total cost of installation depends on the type of hydrant system you’re installing and the size of your house, it usually costs $7 to $40 per square foot to install hydronic radiant floors. This means if you want to install radiant flooring in the entire 1,500-square-foot house, the range is between $10,500 and $60,000.

The average cost is $12 per square foot (without new flooring) and $20 per square foot (with new flooring).

The cost to install panel radiators and fin-tube baseboards will vary as well. You can choose to hide the pipes within the wall or run them along the bottom of the wall. Depending on the installation method, the number of heat emitters, and the size of your house, it can cost anything between $4,000 to $15,000.

The running cost will be $60 – $160 per month (based on 4 hours of daily usage). This is significantly less than the electric heating systems that would cost you $90 – $300 per month.

Are there any disadvantages of hydronic heating solutions?

Like any other system, hydronic heating does have its own shortcomings:

  • It takes longer to heat your home compared to forced-air heating
  • You need to pay higher installation costs upfront
  • Requires careful planning before installation
  • Hard to access piping and troubleshoot if a problem comes up
How radiant heating is different than forced air heating?
Radiant Heating Forced-Air Heating
Heats your home’s surfaces via radiation Blows hot air to warm your home up
Distributes heat evenly throughout the room There may be uncomfortable spots in the room
Doesn’t affect humidity Can distribute humidity throughout the house when paired with a humidifier
Up to 35% more energy-efficient Less energy-efficient
High installation cost High maintenance cost
What does the future of the Hydronic Radiator Industry look like?

According to the technavio report, the radiant heating and cooling system market share will grow by $2.21 billion from 2021 to 2026. About 45% of this growth will originate from North America.

Another report from Allied Market Research shows that the global underfloor heating market size will reach $8.39 billion by 2030, growing at a CAGR of 6.5% from 2021 to 2030. This includes both electric and hydronic-based systems.

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Written by
Varun Kumar

Varun Kumar is a professional science and technology journalist and a big fan of AI, machines, and space exploration. He received a Master's degree in computer science from GGSIPU University. To find out about his latest projects, feel free to directly email him at [email protected] 

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  • Radiant heating provides uniform heat and is both efficient and relatively inexpensive to operate. Efficiency is high because radiant heat raises the inside-surface temperature, thereby providing comfort at a lower room-air temperature than other systems can provide. This is the reason why radiant heating is very important!