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Frequently Asked Questions about Electric Thermal Storage heat

Below are answers to several questions about ETS heat. Click the links below to jump to a specific question. 

 Introduction to Electric Thermal Storage (ETS) heat

Is Electric Thermal Storage new? I've never heard of it.

ETS has been around for decades, and is commonly used in Europe and Canada. Newer electricity rate options in Maine have lowered the cost to heat with ETS. And, when compared to the high and unpredictable cost of other heating fuels, such as oil or propane, ETS heat makes more sense than ever!

ETS heaters provide comfortable, steady heat that's easy to use and requires little to no maintenance. When combined with lower-cost off-peak electricity delivery and supply rates, the low operating costs of ETS heaters makes them an attractive way to heat your home and save money on your heating bills.

How does it work?

ETS heaters contain electric heating elements surrounded by special high-density ceramic bricks that can store large amounts of heat for extended periods of time. At night, during off-peak hours (8 p.m. to 7 a.m.) the bricks store electric energy as heat. Some of that energy is used to provide heat at night, and the rest is stored to release heat during the day when electricity prices are higher.  

I thought electric heat was expensive. How is ETS different?

Electric Thermal Storage heat uses off-peak electricity, which costs less to generate and deliver at night since demand is lower during those hours. Check with an ETS provider to see how much you could save with ETS heat!

What types of ETS heaters are available?

There are two different styles of ETS heaters. ETS "room unit" heaters are installed in a specific room or area and provide supplemental heat in that space. Some heat will spread into other areas as well, depending on the layout and air flow at your location. ETS forced-air or hydronic central heating systems are similar to an oil furnace or boiler. ETS equipment can also be used as a water heater or heat pump booster. 

Contact an ETS provider to learn more about the different types of ETS heaters.

How do I get the heat out of the heater?

Just like any heating system, you can adjust a thermostat to your desired comfort level. The temperature on the thermostat will trigger the ETS heater to release heat, either by operating a blower to circulate hot air or by operating pumps to circulate hot water, depending on the type of system being used.

Does an ETS heater store "cold" in the summer time?

No. An ETS heater can only store heat. Cool storage requires a different storage medium currently not developed for use in the average home.

How big is an ETS heater?

ETS heaters vary in size. Check with an ETS provider for details and sizing information on each type of ETS heater.


How much does an ETS heating system cost?

Purchasing and installing ETS heat is an investment to save on your heating bills for years to come. Plus, ETS heaters start paying for themselves as soon as you use them!

The price to purchase and install ETS heat - either a single room heater or a whole house heating system - will vary depending on the size you purchase, and the specific details of your location. Contact an ETS provider for specific pricing information.

How much does it cost to operate my ETS heater?

If your ETS heater is separately metered, it can charge during off-peak hours using an electricity delivery rate specifically designed for ETS heaters, called Rate A-LM. Or you can put your entire household's electricity usage on a "Time-Of-Use" (TOU) electricity delivery rate. 

Click here for the most recent electricity delivery rate options, including Rate A-LM, and TOU rates Rate A-TOU and Rate A-TOU-OPTS.

Electricity supply companies may also offer an off-peak electricity supply option to use with your ETS heater. Your ETS provider may be able to provide you with more information. The MPUC website also has a complete list of electricity supply options on its website.

If you do not meter your ETS heater separately, it will use the same electricity delivery rate and electricity supply rate that you use for the rest of the electricity used at your location.

How much money will I save on my heating bills?

The amount of money you save on your heating bills will vary based on several factors, such as the type of ETS heater you use, the layout of your home or business, and the amount of heat you use. Contact an ETS provider for more detailed estimates on cost and potential savings based on your specific location and needs.

Purchasing an ETS heater

I have a 1,000 square-foot home. What size equipment do I need?

There are several factors involved in determining the correct size(s) of equipment for your needs. A heat loss calculation should be performed to determine the appropriate model(s). A number of factors are considered, including the size of the area to be heated, construction detail (insulation values), number and size of windows and doors. Using an ETS room heater as a supplement to an existing heating system simplifies this task. An approved ETS provider can help you choose the model that is right for your home or business.

Where can I purchase an ETS heater?

Click here to find an ETS provider.

How will my ETS heater be delivered?

The ETS provider you purchase your ETS heater from will coordinate the installation as well as delivery of your ETS heater.

Installing an ETS heater

What steps are involved to install my ETS heater?

The actual installation will vary by home. In addition to the ETS heater itself, there are a few pieces of equipment that need to be connected to the ETS heater as part of the installation. 

  • If you choose the Separately Metered option, you will likely need to upgrade or install a new meter panel. CMP provides the meter, but you are responsible for any electrical work required at your location to connect to the meter.
  • A "control cable," which is a small wire, may need to be connected from the ETS heater to the meter. The control cable sends a signal so that the ETS heater will charge during off-peak hours.
  • A small temperature gauge may also need to be installed. The gauge goes outside your home and connects to the ETS heater by a small wire. ETS heaters use the previous day's temperature as one factor when calculating how much it needs to charge at night to use the following day.
  • If you are installing an ETS furnace or multiple room units, you may need to upgrade the electrical service at your home if it is less than 200 Amp service.

Can I install the heater myself?

No. ETS heaters are 240V directly connected heating appliances and may require a second meter, which we will provide. Licensed electricians are required to do the installation to ensure all local, state and federal electrical and safety codes are adhered to.

How can I locate a qualified electrician/installer?

Click here to find an approved ETS providers and installers who have been trained to install and service ETS heating systems.

Where in my house should I install an ETS heater?

ETS room heaters can be installed wherever you would like to add supplemental heat. They will provide the most amount of heat in an open area, but you can find the right size ETS room heater to fit any area.

An ETS furnace is typically installed wherever other furnaces or boilers are installed, such as a basement.

Does the ETS heater need to be vented?

No, an ETS heater does not need to be vented.

Can I recess the room heater into a wall?

Yes; however, the specified minimum clearances as listed in the heater manual must be adhered to. Failure to comply with stated clearances may cause operational difficulties, risk of fire, injury, or death.

Can I install the equipment in my garage or workshop?

Since garages and workshops are more likely to have dust and airborne particles and may have varnish, paint or other odors present, caution is recommended. Odor amplification and sooting issues can occur more readily in these types of environments. For this reason, we do not recommend using ETS heating in these types of applications.

Why do I need a separate meter for the ETS heater?

CMP offers an electricity delivery rate specifically designed for ETS heaters. In order to properly apply different electricity rates and properly bill for the electricity used by an ETS heater, it needs to be metered separately from the rest of the electricity used at your location.

What if I don’t want a separate meter?

You can still purchase and install an ETS heater without installing a separate meter

You will need to switch to a "time-of-use" rate for all the electricity used at your location, which has lower electricity prices during off-peak hours and higher electricity prices during "shoulder" and on-peak hours. Click here for more information about our electricity delivery rate options.

Charging an ETS heater and storing heat

When can my ETS heating system charge to store heat?

ETS heaters that are metered on Rate A-LM can only be charged during off-peak hours, from 8 p.m. at night until 7 a.m. the following morning. ETS heaters that are metered on a "Time-Of-Use" (TOU) rate can charge during all hours, but it will cost more to charge outside of off-peak hours. Click here for more information about our electricity delivery rates.

Do I need to set my ETS heater so that it charges?

Your ETS heater will charge automatically if it needs to. The meter sends a signal to the ETS heater so that it will start charging at 8 p.m. and stop charging at 7 a.m. automatically.

Can I override the charging time to charge my ETS heater during on-peak hours?

If your ETS heater uses rat A-:LM, you can't override the charging time because that rate is designed to only be used during off-peak hours. If you charge your ETS heater outside of off-peak hours, you may be removed from rate A-LM. 

If you select a time-of-use rate option, your ETS heater can charge any time, however it will cost more during on-peak or shoulder hours. 

How does the ETS heater know how much it needs to charge overnight?

An ETS heater uses several factors to determine how much to charge overnight in order to provide enough heat the following day. These factors include the previous day's temperature, the amount of heat left in the ETS heater, and how much the ETS heater has charged during previous nights.

Can I tell how much heat is left in the ETS heater?

The ETS heater does not display how much stored heat remains. To get the most benefit from your ETS heater, it should be sized so that it fully charges during off-peak hours (8 p.m. to 7 a.m.), and releases all of the stored heat while it is not charging (7 a.m. to 8 p.m.).

What happens if I run out of heat?

It is important to size ETS heaters appropriately to ensure you have adequate storage to meet the heating requirements of the area, especially if you’ve installed a whole-house system.  However, if you’re using an ETS room heater as a supplemental source of heat, with your existing system as back-up, this situation should never arise.

What happens if the ETS unit is charged, and I don't need heat? Is that heat wasted?

ETS room heaters are well insulated, so the majority of the heat is stored in the bricks until needed. The ETS heater will calculate how much it needs to charge every night, so that a heater will charge less when it's not as cold, and charge more during the coldest part of the winter. Operation is fully automatic.

How long will the ETS equipment hold heat?

If sized properly, the equipment can provide the desired level of comfort 24-hours a day. The heater’s brick core, which is used to store the heat, is well insulated to minimize heat loss when heat is not needed. The heating equipment has the ability to discharge heat even while it is charging or storing heat during off-peak hours.


What type of maintenance is required?

Like most electric heating systems, ETS systems require very little maintenance, if any. It is suggested to regularly clean around the heater and make sure no debris falls behind the equipment. Unlike existing oil furnaces, ETS systems do NOT require annual maintenance or tune-ups.

What is the life expectancy of the heater?

ETS equipment is designed to provide you with many years of trouble-free operation. Life expectancy depends on proper sizing, installation, and the environment it is operating in. ETS heating systems have proven to be very reliable. Here in Maine, many heaters installed by CMP during the 1980s are still running well and keeping homeowners warm.

I would like a different color heater than what is offered. Can I paint the heater?

The heaters are painted with a specially formulated high-grade urethane powder paint that is baked on to provide high scratch and stain resistance and easy to clean finish. The neutral colors selected blend with most any background decor. Although the heaters can and have been repainted in the field, painting over the factory paint will not provide the same durability and performance.

Renewable energy resources

Can ETS units be used with Renewable Energy Resources?

Yes. Since ETS heaters are storage devices, they can serve as a battery to harness renewable power generated from sources such as wind or solar. ETS heating systems help fully utilize these variable generation resources to provide environmental benefit as well as help reduce our dependence on foreign oil imports.

Energy efficiency

Should I weatherize my home before purchasing an ETS heater?

We recommend that your home or business be properly weatherized as an effective way to reduce your overall energy costs - during the winter and all year long.

You can purchase an ETS heater if your home is not properly weatherized, however you can maximize your savings by using ETS heat in a well insulated and weatherized area.

Where can I find more information about weatherization projects?

Efficiency Maine has information about weatherization programs and incentives. Download their brochure, which lists all of Efficiency Maine's programs for residential and business customers. Visit to learn more.



 Benefits of ETS heat

  • Save money on your heating bills compared to many other heating fuels
  • Clean, 100% efficient heat
  • Convenient and easy to use
  • Comfortable, steady heat
  • Low maintenance - no regular cleaning, service, or wood logs or pellets to store and carry!
  • Supports the use of renewable power sources such as wind


Save even more by weatherizing

The size of the ETS unit you'll need depends on several factors, such as the size and layout of the area being heated, and the level of insulation in your home or business.

If your home or business is not properly insulated, you may want to consider insulating and weatherizing your house before purchasing an ETS unit. Efficiency Maine offers information and resources related to insulation and weatherization projects.

Download a brochure that lists all of Efficiency Maine's programs.