As energy costs rise and homeowners look for more space-saving, efficient solutions, tankless hot water coils are becoming an increasingly popular choice for domestic hot water. These compact systems are typically integrated into existing boilers and provide on-demand hot water without the need for a separate tank.
If you’ve ever wondered how to simplify your heating setup and still enjoy consistent hot water, understanding how a tankless coil works may offer the clarity you need.
What Is a Tankless Hot Water Coil?
A tankless hot water coil is a type of heat exchanger that is typically installed inside a boiler. Instead of storing hot water like a traditional water heater, it heats water instantly as it flows through the coil. When a hot water tap is turned on, cold water passes through the coil, which is surrounded by the hot water from the boiler. This quickly transfers heat from the boiler to the domestic water, delivering immediate hot water to the faucet or appliance.
How It Works
The concept is straightforward:
The boiler is heated—either by oil, gas, or electricity—maintaining a supply of hot boiler water.
When you open a hot water tap, cold domestic water enters the copper coil.
As it passes through the coil, it absorbs heat from the boiler water surrounding the coil.
The heated water is then delivered directly to your faucet or appliance.
There is no storage tank, so hot water is produced only when needed, making this an energy-efficient option under the right conditions.
Advantages of Tankless Hot Water Coils
1. On-Demand Hot Water
The system provides hot water immediately and continuously—as long as the boiler is running and has enough heating capacity.
2. Space Saving
Since there’s no storage tank involved, this setup is ideal for homes with limited utility room space.
3. Energy Efficient (in heating seasons)
During colder months, when your boiler is already operating for space heating, the tankless coil utilizes that existing heat to also provide domestic hot water—resulting in efficient dual-purpose use.
4. Lower Initial Cost
Installing a tankless coil in an existing boiler is typically more affordable than buying and installing a separate water heater.
Things to Consider
While tankless hot water coils offer several benefits, they also come with a few limitations:
1. Boiler Dependency
The system relies entirely on the boiler being hot. If the boiler is not running (e.g., in the summer), the system may be less efficient unless the boiler stays warm year-round.
2. Inconsistent Hot Water in High-Demand Homes
In homes with high or simultaneous hot water demands, the coil may struggle to keep up, resulting in fluctuating temperatures.
3. Hard Water Scaling
Just like with tankless water heaters, mineral deposits can build up inside the coil over time. This reduces heat transfer efficiency and may require periodic flushing or maintenance.
4. Reduced Efficiency in Warm Months
Since the boiler must run just to heat water (not space) in warmer weather, energy use may increase compared to other options like standalone tankless water heaters or hybrid systems.
Best Use Cases
Tankless hot water coils are ideal for:
Homes with an existing boiler system (especially in colder climates)
Small to medium-sized households with moderate water demand
Buildings with limited space for traditional water tanks
Residents seeking a budget-friendly way to add hot water capability
For larger homes or families with high simultaneous water usage (multiple showers, laundry, dishwasher), supplemental solutions may be necessary.
Maintenance Tips
To keep your tankless coil running efficiently:
Flush the system annually to remove mineral buildup
Monitor water pressure and flow rate for signs of clogging
Have the boiler serviced regularly to ensure even heating
Consider installing a mixing valve to help stabilize temperature output
The tankless hot water coil is a practical and compact solution for domestic hot water needs, especially for homes already equipped with a boiler. It provides hot water quickly, saves space, and works efficiently during the heating season. While it may not be the best fit for every household—particularly those with high year-round water demand—it offers a smart and cost-effective option for many.
If you're looking to simplify your system and make use of your boiler for more than just heating, a tankless hot water coil could be the perfect addition.
