Can I Use a Tankless Water Heater for Radiant Heat?

Most radiant systems obtain their hot water from a demand water heater with a storage tank, condensing boiler, or a cast iron boiler. Most homes prefer to derive their radiant heat from a tankless electric water heater because of its many benefits and its cost savings.

Many homeowners prefer tankless water heaters over cast iron boilers for radiant heat because they use less energy and cost less to install. They also have good technology built into them and tend not to run out of hot water easily.

tankless water heater for radiant heat

Can I replace my boiler with a tankless water heater?

Tankless water heaters are compact, and you can install many of them anywhere. They take up very little space in a home compared to a combi boiler. They can be mounted on exterior walls and provide endless amounts of hot water.

Even though they are not always commonly used for this application, their output temperatures match the requirements of a radiant system. It also reduces the time spent in maintaining the system because they are durable.

The best benefit to using a tankless water heater is because you will receive an even supply of heat throughout the home, and it will be constantly warm. It means that your floors will never be cold because of the quick return on hot water.

Tankless Water Heater Advantages

Tankless water heaters have a high-efficient water heating system and give off low NOx gasses.

In the long run, they cost less money even though with some models installation may be higher.

Experts recommend the Takagi T-H3. It provides 10 GPM of hot water, and you can fit it for natural gas or propane. This system is very efficient with a low NOx. It keeps the hot water at an even temperature despite the water flow rate and recirculates for quicker delivery. It comes highly recommended for larger homes.

The major factor for using a tankless unit is that they are durable and lasts for a long time. Tankless water heaters generally last for 20 years which is far superior to space heating and other methods. Over time, owners spend significantly less on the hot water heater.

They also come with a warranty that spans anywhere between 10-20 years on average. They are simply a better value overall.

They take up less space than any other system. Tankless systems are the size of a small suitcase. They also install quite easily on a wall and are lightweight. These systems don’t require a large amount of floor space in the garage or basement.

Can you run out of hot water with a tankless water heater?

These systems are ideal because, as stated, they give hot water on demand (meaning that it can run while people are showering and appliances like a dishwasher are being used and still not run out of hot water), and it has an endless supply.

You have an instant supply of hot water because most systems contain a recirculation system. In terms of a radiant heating system, your floors will not get cold. They will continue to remain warm. The water is always warm and ready.

Tankless water heaters tend to have one to two heat exchangers, modulating gas valves, multiple sensors, and electronic control boards. The entire process is computerized and automatically regulates heat. Water does not under or overheating. The temperature remains constant.


There is a high initial cost involved to install them. However, the cost savings and how long they run balance this out. The gas burners are very strong, as well, and may not be ideal for smaller usages.

If you have hard water, you will require a water softener. Additionally, some systems are very touchy when it comes to fluctuations in pressure and heating water quality.

radiant heating system

Why Combine a Tankless System with Radiant Heating?

Radiant heating is wonderful for a radiant floor heating system. It is commonly used in bathrooms, garages, and living areas but can be incorporated anywhere in the house. It works by warming air from a heated floor which ends up circulating heat throughout the area.

Radiant heating is energy efficient compared to baseboard heating. Combined with a tankless water heater, the cost savings are very high. There is no heat loss experience as in forced air heating, either.

For allergy sufferers, the complete tank water heater or storage water heater system is ideal. Air and dust don’t circulate throughout a room. You also don’t have to clean as much. There are also no drafts.

Using a tankless system with radiant flooring means that the BTU and energy consumption do not increase. Everything will run very efficiently. Tankless systems only produce the right amount of heat required. Energy is used on direct hydronic heating in a hydronic system.

Tankless systems are also cleaner to run. If domestic hot water runs through pipes or pex tubing, sediment can build up, causing the system to overcompensate. In the end, if you don’t clean the sediment, the traditional water heater ends up breaking down.

Since tankless systems tackle all these issues, they last much longer overall, and they create less of a hassle for the homeowner.

However, before investing in a tankless hot water heater, consult a plumber or manufacturer to discuss what size and type are needed for your radiant heat. Different models have various capabilities, and you want to ensure that everything runs smoothly.

What size tankless water heater do I need for radiant heat?

Usually at least 5.2 gallons. The reason for this is that the water temperature will need to increase from 40 to 105°. To do this, homeowners will need to heat a minimum of 5.2 gallons of potable water.

How long can a tankless water heater run continuously?

They usually only run continuously for three hours per day. Tankless systems only come on when there is a demand for them.

Tankless water heaters are perfect for hydronic radiant heating or a hydronic heating system. They are energy efficient and require a smaller footprint than the other alternatives. The cost to run radiant heating off these systems is lower despite the upfront costs being a bit higher for some systems.

Heat will remain continuous with these systems. There are no lows or highs. Hot water is on-demand with these systems, and they don’t tend to run out even when multiple resources are used. They provide a better alternative when using radiant heat, and you can easily incorporate them into this system.

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