Boiler vs Water Heater: propane gas vs electric water heater comparison

Everyone needs the most reliable and energy efficient set up with the lowest possible upfront cost when it comes to heating for family needs. If you are not a plumbing professional, it is a good idea to get some advice on boiler vs water heater problem. What is better, propane or hot water heater, tankless or boiler? We’ll help you to make the right choice.


Boiler vs water heater: domestic water heating for showering, bathing and washing

When it comes to heating water for washing, bathing and showering, tank heaters (both electric and gas) are commonly referred to as boilers.

Electric boiler vs water heater (potable water systems)

Electric tankless water heaters are very  compact and efficient devices. They are high power devices, so you do need sufficient power. The main advantage is that tankless heater only makes heated water when you need it. And since it’s compact, you can install it next to the tap and get hot water right away and reduce heat loss in the pipes. There are even models of heaters located directly on the tap.

electric vs gas tankless water heater
EcoSmart Electric Tankless Water Heater

So, electric tankless (also known as point-of-use) WH are small, durable and quick. Their bad is that they need THICK wires with a dedicated breaker. To install the device you need worker with electrical permits and with plumbing permits (2 workers or one expensive certified in both). Tankless units may be very durable, but it depends on the quality of the water. If it’s hard, you have to descale the heater as much as 2x a year.

boiler vs water heater
A.O. Smith electric 40 gal boiler vs water heater

Electric boilers (tank water heaters) consume the same power to heat 1 gallon of water per 1F degree, but they do it slowly and store heated water. Since hot water is stored in the tank, despite the thermal insulation, some thermal energy is lost to heat the air. And due to its large size, you cannot install a tank near each tap. Therefore, the length of the pipes from the heater to the faucets is longer, hot water does not come immediately and additional losses arise in a pipeline. If your boiler isn’t large enough, and you’re showering for a long time, you need to blend hot and cold water few times to get constant temperature. With a tankless water heater you just set the temperature and have no need to blend it.

The advantages of electric boilers are:

  • If the water in your area is hard, they will last way more than the tankless will
  • Typical electric power of boiler is 1-2kW, therefore no special wiring is required
  • Boiler installation will require at least 3-4 hours less working time and $200-300 less in additional material costs

Boiler vs hot water heater: conclusions

If you have space to install a large electric boiler, this is the cheapest and hassle-free solution. Otherwise, install an on-demand heater, the higher cost will pay off over time due to the higher efficiency.

NG or propane tankless water heater vs boiler

Tankless heaters

On-demand (tankless) natural gas or propane water heaters are pretty convenient and reliable. I really like it for several reasons. Similar to electric, gas tankless water heaters make hot water only when you need it. If it is close to the tap, you get hot water almost instantly only having to wait for it to travel through the plumbing.

boiler vs hot water heater
Eccotemp Natural Gas Tankless Water Heater

Gas tankless heaters may be very powerful and work flawlessly for decades. All you need is to flush it annually if your water is hard. For this purpose you can set bypass valves at the outlet and inlet. When you need to flush mineral scale deposits out, you turn off the water in and out, and open bypass valves to flash the heat exchanger with vinegar.

With an on-demand gas heater you have endless hot water. Simpler models don’t modulate the flame and come with a low to high dial so you need to mix the water by the faucets.

propane vs electric water heater
Ridgeyard LPG Heater

The only con is the initial cost. It may be high and depending on the gas service provided, gas tubing may require up-sizing.


electric vs propane tankless water heater
A.O. Smith Gas Water Heater, 40 gal

If the space for placement of a water heater is not a problem and hot water consumption is small, a tank unit may be more economical. They are not dependent on the incoming water temperature, need less maintenance. Usually all you need is to flush out the bottom with a garden hose sometimes.

A boiler heats the water slowly, so it doesn’t have to use a huge flame and doesn’t need big gas pipe. The disadvantages are similar to electric tank units: large size and weight, heat losses, the temperature gradually drops when you use 50% and more of the tank volume, and the hot water volume is limited by the size of the tank.

Tankless water heater vs boiler combo

New combo units have their advantages, and they are efficient, save space and like tankless water heaters can heat water on demand. The only negative is that if it breaks, you have no hot water and radiators are cold too.

So where possible I think you should consider a system with separate devices. For example, am currently dealing with a case with a broken ventor motor on boiler and the customer hasn’t both hot water and heat for two weeks due to poor parts availability. It’s scary to even imagine how unpleasant it would be in the midst of cold weather.

Propane vs electric water heater

For Propane vs electric water heater, it depends largely on relative fuel costs. For example, in Ohio there is no government-subsidized electricity and propane prices vary with time and volumes.

Electric heating is usually more expensive and less desirable unless it comes from the low environmental source as wind or solar. Sometimes consumer don’t consume all the electricity and electric heating can make sense.

Nevertheless, in some areas the electric power is cheap. Considering that the efficiency of electric heaters is very good and heat does not escape through the vents, this might be a good choice. Some electric company even offer a rebate to customers who switch to an electric water heater from a propane unit and it pretty much cover the cost of the water heater. Cost of operation may be about the same when propane prices are high (see also Bradford White vs Rheem Water Heaters Review).


In my opinion, when it comes to gas heaters, the tankless is better than tank. If you are primarily are home beginning and end of day, they help to avoid major standby losses. Gas on-demand units are reliable, long-lasting and inexpensive to maintain. Even if you need need a boiler for space heating, gas tankless heater near the tap is better than combo unit. The distance from where the tank installed usually is too far away from the use points (sinks, etc).

Radiant heating systems – boiler vs water heater

In the context of space heating, a boiler is a device for heating water in closed-loop systems. And some plumbers use domestic water heaters as a boilers.

Water heater advantages

Using a high-quality domestic water heater instead of a boiler helps to save money because it is cheaper. However, there are many other benefits as well.

Boilers are designed to make a lot of hot water for radiators and use large amounts of gas. Heater firebox, chimney and water temperatures are high. On lower temperatures boilers work worse and can even be damaged due to “cold shocking”.

tankless water heater vs boiler
Rinnai Natural Gas Heater

Water heaters are simpler devices with a less heating power. A condensing water heaters, are around 95% to 98% eff. and it is usually much higher than boilers efficiency.

Although water heaters are cheaper and more efficient,you shouldn’t use cheap water heater as a boiler. The heater should have high efficiency, enough heat power and be made of reliable and long lasting materials. High efficiency water heaters doesn’t heed chimney and work with plastic vents. They are also direct vent devices and draw air from the outside of your home for combustion, and this saves money.

Why boilers are still used for heating?

Boilers are high-power devices for space heating. They are designed to be used for this task. For example, Rinnai Tankless Water Heaters are certified to the Standard for Gas Water Heaters ANSI Z21.10.3/CSA 4.3 that includes heaters for use with applications commonly referred to as open loop systems.

Units for use in closed loop systems are certified to the Standard for Gas-Fired Low Pressure Steam and Hot Water Boilers ANSI Z21.13/CSA 4.9 – space heating only (closed loop) systems (see also Rheem vs AO Smith Water Heaters.

These are two different standards and the requirements for these devices are different. For this reason, Rinnai does not recommend the use of its Tankless Heaters for closed loop heating applications and will not honor warranties for units.

Therefore, the using a boiler is a versatile and reliable solution. The use of water heaters for closed loop radiant heating tasks is possible, but requires an understanding of the physics of the process and engineering calculations.

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