Summary:
- An indirect water heater is a storage tank heated by your boiler through a coil, not by its own burner or element.
- Indirect water heaters are a more efficient choice for most homes with a boiler.
- Because there’s one heat source, there are fewer burners and flues to maintain.
- It works best paired with a high-efficiency boiler, which makes a boiler replacement the ideal time to add one.
- Compared with a tankless water heater, an indirect tank delivers a large stored supply for several fixtures at once.
How Does an Indirect Water Heater Work?
An indirect water heater is an insulated storage tank with a heat-exchanger coil inside. Hot water from your boiler circulates through the coil, heating the household water around it. The two never mix. Your boiler treats the tank as its own heating zone, firing whenever the tank’s thermostat calls for heat.
Here’s the cycle in plain terms:
- You use hot water, and cold water refills the tank.
- The tank’s thermostat senses the drop and calls the boiler.
- The boiler sends hot water through the coil, usually as a priority zone so the tank recovers quickly.
- The tank reaches temperature, and the boiler goes back to space heating or shuts off.
The energy in the tank lets the boiler fire less often for hot water, which the U.S. Department of Energy notes saves energy. Its guidance adds that an indirect tank paired with a high-efficiency boiler and a well-insulated tank can be the least expensive way to provide hot water.
Benefits of an Indirect Water Heater
The main benefits are efficiency, a large hot water supply and simpler equipment. Because your boiler does the heating, there’s no second burner, flue or heating element to maintain. A well-insulated tank holds its heat, so the boiler doesn’t have to fire constantly to keep water ready.
- Efficiency: One high-efficiency heat source serves both heating and hot water.
- Strong hot water supply: A stored tank backed by a powerful boiler recovers quickly, which helps when several people shower in a row.
- Durability: Many indirect tanks are lined or made of stainless steel to resist corrosion.
- Fewer appliances: No separate gas water heater means one less vent and one less burner to service.
Are there downsides?
Yes, a few. You need a boiler, so homes with furnaces or heat pumps aren’t a fit. In summer, the boiler still fires to heat water, which is why pairing with a modern high-efficiency boiler matters. And a combined system usually costs more up front than a separate standard water heater, though installation and maintenance can cost less because there’s one heat source and fewer parts.
Indirect Water Heater vs Tankless: Which Is Better?
An indirect water heater stores hot water heated by your boiler, while a tankless water heater heats water on demand with its own burner or element. Indirect tanks are well suited to homes with a boiler and higher simultaneous hot water use. Tankless units suit homes without a boiler or with limited space.
| Indirect water heater | Tankless water heater | |
|---|---|---|
| Heat source | Your boiler | Its own gas burner or electric element |
| Hot water supply | Stored tank, strong recovery from the boiler | On demand; flow rate limits how many fixtures can run at once |
| Space | Needs floor space for a tank | Wall-mounted, compact |
| Venting | None of its own | Gas units need their own venting |
| Best fit | Homes with a boiler, especially when replacing it | Homes without a boiler or with tight space |
Don’t confuse an indirect tank with a tankless coil, which heats water directly inside the boiler with no storage tank. Tankless coils rely on the boiler firing every time you need hot water, and the Department of Energy notes they can be an inefficient choice for many homes. An indirect tank stores heated water, so the boiler fires less often.
Is an Indirect Water Heater Right for Your Home?
An indirect water heater is usually a good fit if you have a boiler in good condition or are replacing one, your current water heater is near the end of its life, and your household uses a fair amount of hot water. The best time to add one is during a boiler replacement, when the piping and controls can be designed together.
If you’re planning a new boiler installation, ask us about adding an indirect tank in the same project. You get one coordinated install, and your new high-efficiency boiler handles both jobs. Read more about choosing an efficient boiler in our guide to high-efficiency boilers for Plymouth County homes.
Not every home suits an indirect tank. We also install standard and power vent water heaters, and we’ll recommend the option that fits your home and budget.
Frequently Asked Questions
Does an indirect water heater need a boiler?
Yes. It relies on a boiler as its heat source. Homes with a furnace, heat pump or no central hydronic system need a different type of water heater.
Can I add an indirect water heater to my existing boiler?
Often, yes, if the boiler has enough capacity and is in good condition. A plumber will check its output, controls and piping before recommending it.
Does the boiler run in summer with an indirect water heater?
Yes, the boiler fires to reheat the tank when you use hot water. A well-insulated tank keeps those cycles short and less frequent.
Do you install indirect water heaters?
Yes. Emma Plumbing and Drain Services installs indirect water heaters, on their own or alongside a new boiler, across Plymouth, Norfolk, Bristol and Middlesex counties.
Get an Indirect Water Heater Installed by Emma Plumbing and Drain Services
Whether you’re replacing a boiler, an aging water heater or both, we’ll help you decide if an indirect water heater makes sense. Emma Plumbing and Drain Services has served Massachusetts homeowners since 2007, under MA Master Plumber License #15828. We offer warranties and financing on water heater and boiler installations, with upfront pricing. Explore our water heater installation services, call 857-398-8840, or request a free quote today.
