combi boiler (combination boiler) combines hot water tank with boiler into a single high-efficiency unit

What Is A Combi Boiler And Why Should You Buy One?

Learn the pros and cons of combi boilers, and what brands make the best systems.

Written by
Kate Webb
May 28, 2020

What is a combi boiler?

A combi boiler, or a combination boiler, combines a hot water tank and boiler into a single high-efficiency unit. Combi boilers provide your home with both hot water and central heating.

What’s the difference between a combi boiler and a regular boiler?

A combi-boiler heats water directly from the water main, as you need it, so there’s no need for water storage tanks. Combi-boilers are compact, so they’re great for homes with limited space. Because these units heat water on demand, they tend to be more energy efficient.

A regular boiler requires a tank to store cold water and a cylinder for hot water. This setup takes up more space, but works well for large homes that use a lot of hot water. Regular boilers continuously heat a full tank of water, so they typically use more energy than a combi-boiler.

What are the pros and cons of combi-boilers?


Cheaper - Combi boilers have a lower operating cost because they only heat the water you need, rather than continuously heating a full tank of water. Combi boilers are also less expensive to install. These systems aren’t as complex as regular boilers and require fewer parts.

Faster - With no tank to heat, combi boilers offer an unlimited supply of hot water as soon as you need it—even if you’re third in line for the shower.

Great water pressure - Speaking of showers, combi boilers heat water directly from the main, so they’re not affected by pressure issues.

Cleaner - Without regular maintenance, water tanks can accumulate mineral build up, rust, and debris. Because there’s no tank, the water from combi boilers tends to be cleaner.


Back-up hot water - If your combi boiler breaks - which should be very rare - then there’s no extra supply of hot water.  Ask Tetra about same-day boiler service:(

Limited use - If a combi boiler is incorrectly sized for a home, it may be strained in larger homes when many showers, faucets, dishwashers, and laundry machines are running at the same time. This may be an issue if you have 6+ people in the house.

Why we recommend combi boilers

We recommend combi boilers primarily for the dramatically increased efficiency and cost savings. Combi boilers are less expensive to purchase and install, and their efficiency means you’ll spend significantly less on energy bills over time. If you require service, combi boiler repairs tend to be straightforward and inexpensive. There’s a reason we’ve installed over 1,200 of these units in Eastern Massachusetts.

Brands we recommend

Burnham - Burnham (U.S. Boiler Company) makes some of the safest, most reliable, durable heating products in the U.S. Known for their efficiency, Burnham offers boilers with efficiency ranges as high as 95% AFUE and they regularly publish their energy certifications.  They tend to be a little more expensive than other brands however.

HTP - This American heating and hot water manufacturer is laser-focused on high efficiency. Their products are extremely efficient, user friendly, and low maintenance. They strive to incorporate new technology, and renewable energy sources whenever possible.

Navien - Navien was the first company to introduce a highly efficient, environmentally friendly condensing boiler. They've since grown to be a global boiler manufacturer and are the leader in wall-hung condensing boilers. They are one of the most popular products in Massachusetts.

The bottom line

Combi boilers can’t be beat in terms of value, simplicity, footprint, and efficiency. Speak with a Tetra representative today ( to discuss your options.


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