How Big Of A Water Heater Do I Need For Radiant Heat?

How Big Of A Water Heater Do I Need For Radiant Heat

Using a water heater for radiant heat has become a more cost-effective, efficient, and environmentally friendly option for many homes in recent years.

How big of a water heater do I need for radiant heat? The exact water heater size you need will depend on your average water usage. You need at least a 30-gallon capacity storage tank water heater for a house with up to two people. Homes with two to three people will need a 40-gallon tank, while households with four people will need a minimum of a 50-gallon capacity tank. Families with five or more people will need an 80-gallon capacity storage tank water heater.

But the size of your household is not the only consideration when deciding how big of a water heater you need for radiant heat. Keep reading to learn some of the other key factors. 

How Do Water Heaters Work?

A water heater works by allowing cold water to enter the tank through the dip tube, and the electric heating elements inside the tank heat the water. The hot water in the tank is moved throughout the home through the heat-out pipe.

Benefits Of Using Water Heaters

Many people are transitioning from boilers to water heaters, but that’s not only because of its cheaper overall cost and ease of maintenance. Using it for radiant floor heat also solves frequent maintenance problems as water heaters can run for many years without developing any major issues.

Rest assured that water heaters generally do a better heating job than boilers because they are more efficient. Plus, they cut down your energy bills.

Some people question the ability of water heaters to produce enough hot water for their household heating needs. Others seem to be concerned about the safety of the system. However, these sentiments are mostly unfounded, if not completely untrue.

In addition to using a water heater for radiant heat, you can choose to kill two birds with one stone by designing the system to serve a dual purpose, known as a combo system. In other words, it has two hot water outlets – one for the heating system and the other for portable water or domestic hot water.

This eliminates the need to invest in two separate heat pumps for your different household water heating needs, meaning you are getting two heating pumps for the price of one, and at the same time, saving space.

However, keep in mind that using your water heater for dual purposes may mean having a higher water temperature at your faucet. This is because the heater would maintain hotter temperatures while serving as a radiant heater. 

As a solution, you can add an automatic mixing valve, which mixes hot and cold water and set it to the desired water temperature you need for your domestic hot water uses.

What Size Should My Hot Water Heater Be?

water heaters display of different sizes
Source: Radovan1

In addition to the size of your household, here are other factors to consider when answering the question: how big of a water heater do I need for radiant heat?

Fuel Source

To narrow down your options and simplify your shopping process, it is important to determine your fuel source. For example, how do you plan to power the hot water heater? Would you be using electricity, liquid propane, or natural gas for fuel?

Physical Size of Water Heater

Think about the space you have in your home. While a big hot water heater is great for large families, it won’t do you much good if it can’t fit into the designated space. You will have to make enough room for the water heater or find a way to cut down on your hot water usage.

BTU Output

If you are thinking of going for a simple, low-budget system that does not have a heat exchanger, you can install any standard water heater as long as the BTU output is sufficient to cover the heating load.

Note that the BTU stands for British Thermal Unit; the standard way to work out how much heat output is required to keep a room warm.

If the BTU output of your heater is not sufficient, then it would not serve the purpose of supplying radiant heat. So, in a nutshell, the sufficiency of your heater depends on the BTU output.

If you think of installing a more sophisticated heat-exchange system, you may need a high-end sealed-combustion water heater with an external heat exchanger.

When water heaters are used for radiant heating, it should be noted that it is indicated in the specifications on the installed water heater if it can be used for such. Generally speaking, the water heater should be used only for heating loads with a maximum output of 75,000 BTUh (British Thermal Unit per hour).

For a typical home, the output of a residential hydronic radiant heating system is between 25 and 35 BTU per square foot. This could go up to 40 BTU for homes with poor insulation.

For the best results, it is important to first calculate the square foot of the space that needs heating. Next, you need to be sure that the capacity of the water heater you choose would be sufficient enough for the heating job.

Disadvantages Of Water Heaters For Radiant Heat

Water heaters have several advantages, as shown earlier. They are cost-effective, conserve space, and can serve dual purposes.  But, what are the disadvantages of using water heaters for radiant heating?

Very slow to pick up when cool

If the water is allowed to cool, water heaters are quite slow in picking up to supply radiant heat when switched on. The solution is to keep it on almost all the time if you want it to continue to supply regular warmth.

Using heaters for radiant heat can void the heater’s warranty

Some heaters may have their warranty voided if used for radiant heating. Although this does not apply to all heaters, some manufacturers believe that using a water heater for radiant heating reduces the appliance’s efficiency.

Heaters can’t maintain very high temperatures (>140°F) for long periods without wearing out easily

Keeping water above 120°F is a very dangerous experiment as water above that temperature is already extremely hot. While the heater can maintain as high a water temperature as 170°, keeping water above 140°F is certainly going to wear out your heater rather quickly.

Final Thoughts

How big of a water heater do you need for radiant heat? This depends on a few different factors, but the main consideration is the size of your household and the average water usage.

Overall, it is important to note that the advantages of using a water heater, compared to boilers, outweigh the disadvantages, particularly for smaller homes. It is a smart, cost-effective, and environmentally-friendly choice.

For larger spaces, though, consistently circulating water at very high temperatures will wear out the heater. This is particularly the case for people who live in places with predominantly cold weather. In the long run, the cost-effectiveness will eventually be canceled by the frequent wear and tear.

Frequently Asked Questions

Still have questions when it comes to radiant heat in the home? Then, check out the answers to some of the more commonly asked questions.

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

On average, a hydronic heating system can cost anywhere between $2,500 and $3,000 per unit. However, there are other costs you need to consider, including labor and the supplies needed for the proper installation of a new hydronic heating system.

What is a good temperature setting for a radiant heat floor?

When choosing the temperature setting for a radiant heat floor, you never want to exceed 85-degrees Fahrenheit. This is our skin temperature, so anything warmer than this may begin to feel too warm. Many people find that the most comfortable temperature range for radiant floor heating is between 75 and 60-degrees Fahrenheit.

What type of heater do you need for hydronic floor heating?

You can choose from a number of different heating sources for your hydronic floor heating, including a water heater, boiler, geothermal heater, solar hot water heater, or tankless water heater system.