When it comes to heating water in your home, there are several options available—each with its own pros and cons. One lesser-known but effective option for certain homes is the tankless coil water heater. These systems don’t require a storage tank and can provide hot water on demand using your home’s heating boiler. In this article, we’ll break down what a tankless coil water heater is, how it works, and whether it’s the right choice for your home.
What Is a Tankless Coil Water Heater?
A tankless coil water heater is a system that provides hot water without storing it in a tank. Instead of relying on a separate water heater, this system uses your home’s existing boiler—which is typically used for space heating—to heat the water as it flows through a special coil inside the boiler.
This type of water heating is considered “on-demand” because it only heats water when a hot water faucet is turned on. There’s no storage tank involved, so there's no energy lost in keeping a large volume of water hot all the time.
How Does It Work?
Here’s a step-by-step look at how a tankless coil water heater functions:
Hot Water Request
When someone in your home turns on a hot water tap—whether it’s in the kitchen, bathroom, or laundry room—the system is activated.Cold Water Enters the Coil
Cold water from your home’s main water supply enters a specially designed copper coil (the “tankless coil”) that sits inside the boiler.Heat Transfer in the Boiler
Your boiler, which is already heated for your home’s space heating, transfers heat to the water through the coil.Hot Water Is Delivered
As the cold water flows through the coil, it’s rapidly heated by the surrounding hot water in the boiler, and then it flows out to your faucet or showerhead.
Since the system only heats water as it’s needed, it avoids the standby energy losses associated with traditional storage water heaters.
Benefits of Tankless Coil Water Heaters
Space-Saving Design
Because there’s no storage tank, this system is compact and ideal for homes with limited space.On-Demand Hot Water
You get hot water only when you need it, reducing energy waste.Great for Cold Climates
These systems are particularly efficient during the colder months when the boiler is already in use for space heating.Lower Initial Cost
If you already have a boiler system in place, the cost to install a tankless coil water heater is often lower than installing a separate tank water heater.
Limitations to Consider
While tankless coil water heaters can be a good solution in some homes, there are a few drawbacks to keep in mind:
Seasonal Efficiency
In warmer months, when your boiler isn’t running as frequently, the system becomes less efficient. The boiler has to turn on just to heat water, which can waste energy.Limited Hot Water Output
These systems may not meet the high hot water demands of larger households. If multiple showers or appliances are in use at the same time, you might experience a drop in water temperature.Dependence on Boiler
If your boiler breaks down, you lose both heat and hot water.
Is It Right for You?
Tankless coil water heaters make the most sense in homes where a boiler is already installed and used frequently—especially in colder climates where the heating system runs for much of the year. They’re not ideal for large families with high hot water demands or for areas with hot climates where the boiler is mostly off.
If you’re replacing an old water heater or upgrading your home’s heating system, it’s worth speaking to a plumbing or HVAC professional to see if this system could be a good fit.
Tankless coil water heaters offer an efficient and compact solution for households with boilers, particularly in regions with long heating seasons. While not suitable for every situation, they can help save energy and reduce utility bills—provided they match your household’s hot water usage patterns.
