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.

Rheem vs AO Smith Water Heaters – Pros, Cons, Comparisons

Hi! There are a lot of questions about water heaters on forums and reviews and I’ve read a lot of those to solve my Rheem vs AO Smith problem when my almost twenty year old heater leaked from the hot water outlet.

rheem vs ao smith


Important! Installation and Labor

Think about installation costs and contractors BEFORE purchasing a heater!

Make sure the price the subcontractor quote is firm. Many of them, especially when working for big box stores charge more for upgrades once they get to your house. I had some experience with Lowes’s contractor.

Both plumbers and stores can charge you with $1000 for the labor part. Some companies install ONLY parts which you bought from them. And they are often much more expensive than Amazon.

Don’t need to agree right away. Ask about local plumbers, HVAC contractors and handyman who could do this job? They tend to do water heaters and are usually much cheaper.

Can you do some parts of the task yourself? For example, purchase and bring home (often free-of-charge) the heater? Usually home owner can turn off the gas and easily drain the water heater yourself. Getting the device and draining it are about 2 -3 hours of “work” that you are paying the contractor for.

Rheem vs AO Smith Natural Gas 50-gallon Water Heaters

ao smith water heater vs rheem
Check the price – Rheem PROG50-40N 50 Gallon Professional Classic Tall Natural Gas Water Heater

I called a HVAC & Plumbing guy to get an in-house estimate and I also made some research Home Depot, Amazon and Lowes to get an estimate. Here are my options.

1) Local Plumber $1875: AO Smith, drip pan, expansion tank, cold water inlet ball valve.

2) HD’s contractor gave me two Rheem options:

  • about $1500 for Rheem PROG50-38N RH60
  • about $ 1600 for Rheem XG50T12HE40U0 12 yr parts &3 yr labor

3) Amazon:

  • A.O. Smith XCR-50 ProMax Plus (10-yr, about $1,021 & free shipping)
  • A.O. Smith GCRL-50 ProMax Short Heater (6-yr, about $900)

Anode rod replacing

The way to replace the sacrificial anode rod can be difficult and require a specialist. So you need to buy the heater that you are confident you are able to do it yourself. Anode in standalone port is easier and cheaper to replace.

AO Smiths rods tend to be harder to replace. Rheem is easier, you can check the video on how to replace the rode.

Sediment flush is very simple on any heater.


ao smith vs rheem gas water heater
A.O. Smith XCR-50 ProMax Plus 50 gal Gas Water Heater

In my opinion, there is no significant difference between the guarantees of Rheem vs. AO Smith. When you buy a heater from a reputable brand (and they both are), the difference in prices for similar models is mostly due to the extended warranty.

For example, the Rheem heaters are all pretty identical and the price difference is just the warranty. Upper models have a slightly better control valve. Any model will likely work for 15-25 years and then will need replacement.

Of course, you can pay more for the unit with 12 year guarantee. And sometimes (rarely) you even will have additional anode in the unit. But my advice is to save the money and buy the six year product. 12-year one has the same tank, so if you replace the anode rod and flush the sediment regularly it’s going to live a long time.

AO Smith has also great customer support. One phone call from your plumber to the company will get you a brand new device in few days with no charge.

Energy efficiency

Energy efficiency of a water heaters is measured in UEF. It is Unified Energy Factor, the method of Department of Energy. The higher the UEF, the higher the efficiency.

For example, AO Smith Professional Classic Plus 48-Gallon Water Heater has UEF 0.80 and Rheem ProLine XE 50-Gallon Gas Water Heater – 0.72UEF, so the AO Smith is slightly better. But both heaters are Energy Star certified, which can lead you to tax breaks in the right state.

Conclusions: Rheem vs AO Smith tank water heaters

Both Rheem and AO Smith are good products and you can’t go wrong with either.

The difference is in personal preferences and the need to save money. Personally, I want to change the anodes myself and see no point in a 12-year or even a “lifetime” tank warranty. So I bought 6-year Rheem heater.

If you don’t want to bother with replacing anodes and and monitoring the technical condition of the heater – just call specialist every few years. And buy Smith with a 12-year warranty. They have great customer service and you will be more confident about that.

Read also our Rheem vs Ecosmart heaters comparison.

Rheem vs AO Smith Tankless Gas Water Heaters

Tankless water heaters are source of “endless” hot water, but they are more sensitive to water quality. Hard water, lack of maintenance (no descaling, no flush and drain), improper installation/venting etc. could significantly shorten the life of the heater. So every model of every brand needs some maintenance on it.

Rheem gas tankless Water Heater
Rheem Gas Tankless Water Heater

When it comes to capacitive heaters, both manufacturers go head to head, for example Tankless Water Heater Condensing Ultra-Low NOx by Rheem has almost absolutely similar specs with 10.0 GPM Indoor Natural Gas Tankless Water Heater by AO Smith.

The vast majority of the water heater components are universal. So, my answer to the Rheem vs AO Smith Tankless Gas Water Heaters question is to choose what’s cheaper and actually do the necessary maintenance on it.

Check the anode every year and replace it if required. Some handyman recommend to loosen and reinstall the anode after buying and before you turn on the water heater for the first time. It will help you to get the anode out later. Drain the sediment out of the water heater at least once a year once a year. Just do that and your heater should last a lifetime.

Rheem vs AO Smith Electric Water Heaters

AO Smith Electric Water Heater
AO Smith Electric Water Heater

Electric water heaters are much more simple than gas ones. They don’t need gas nozzles, ignition automation and are more safe. Tank models are more durable, require less power (due to water preheating), but they are much larger and limited in the amount of hot water.

The main difference between warranty is in anode rod diameter. For example, a 6-year typically has .75-inch anode and 12-year .90-inch rod. So you can easily convert 6 year tank into 12 year one by changing anode each 1-3 years or installing larger one.

So again, the advice is to buy what you like and don’t spend too much. Check the heater for leaks every six months. Check water pressure and ensure it doesn’t exceed 80 psi. These actions will prolong life of any heater.

But my choice is AO Smith heaters, they arrive with detailed manual, easier maintenance, and troubleshoot steps.

EcoSmart vs Rheem Water Heaters

Gas water heating is usually cheaper, but an electric tankless water heater is your choice if you don’t have proper gas supply lines or ventilation system, need a small, quick and durable unit in office suites and all other public buildings. In the United States, there are two leading electric water heater manufacturers: EcoSmart and Rheem and few less popular – Bosh, Stiebel (Germany), Camplux (China), and others.

Read also our Rheem vs AO Smith comparison.

EcoSmart ECO Electric Tankless Water Heaters

Lifetime Warranty, self-modulating technology – unit will adjust power to current water flow. Temperature control in digital 1-degree increments.
Stainless and copper components for high durability and efficiency, six models (8-36KW, 2-6 gallons per minute), 240 volts


EcoSmart gives the most extensive warranty on the market: Residential Heaters ECO8–36, lifetime warranty on electronics, Exchangers, and elements.

EcoSmart also offers SmartBoost unit – a 7.2 kW electric heater ECOTB240 to be connected to a tank gas or electric water heater to increase hot water delivery. SmartBoost will increase the efficiency by 45%, so you’ll get more hot water (like with much larger tank) for the lower price and installation costs. The Ecosmart will adjust pressure settings and power usage to keep a consistent output for you.


Warranty is eligible for tankless electric water heaters installed by licensed electrician/plumber within 30 days of purchase, warranty registration must be filled and post marked within 30 days of purchase. Be careful to register your unit properly.

Service wait times sometimes are long and warranty covers the parts only cost. Labor to repair might be expensive, and it is not a very complex device and you can often make simple repairs yourself if you are handy.


Buying EcoSmart  Electric Water Heater is a good decision. The Ecosmarts is well-reviewed, reliable and efficient units. It is a great choice for most people – has a power range of 5.5 to 36KW that is suitable for appliances from hand washing to large family home in cold climate regions.

Rheem Tankless Electric Water Heater Characteristics

Energy efficient – 99.8%, digital temperature display. Industry leading low flow activation – unit start heating when the tap is turned on low.


Rheem units are one of the most compact tankless water heaters, and it allows to install it right near the sink and minimize hot pipe losses. Besides, the Rheem units are cheap enough to allow energy savings pay off expenses in a reasonable time – in several years, one of the best turnover periods.


Hard water ruins these units fast, so you should put a softener in line ahead of it or clean it annually. It is an important thing you have to factor in the cost of going tankless when your water is hard (see our maintenance manual).

Similar to Ecosmart, if the unit is not installed by professionals, it could get you into an issue upon returning the item.


Rheem units have low flow activation, have nice displays, look great and are cheaper than Ecosmart. But warranty conditions are worse, reliability issues occur, and there are more assembly quality complaints. Nevertheless, Rheem is a great cost effective choice if you need a compact solution.