08/08/2025
Pros and cons of different types of water heaters that everyone should know:
An old friend reached out to me asking about a tankless water heater installation recently. My response was, “You should know a few things about these systems before you make a decision.”
I want her, and everyone, to make an educated decision regarding a water heater purchase. Obviously, all the different types of units will produce hot water to some capacity, but there are many differences between each type of system, and fuel type, that should be carefully considered before you sign any agreements.
I’ll be listing what to expect for each unit in regard to installation and replacement, warranties, maintenance, troubleshooting difficulty and repair cost, efficiency and fuel consumption, service life expectancy, and a few other points that are system specific.
This one is for you Lady, and for anyone who isn’t sure of what type of system that they should invest in. It’s my job to make sure my customers are satisfied with any system I sell them, and I take that very seriously.
Let’s start with a list of a few common types of water heaters:
1- Tank style water heater
2- Indirect fired tank water heater (i.e.- boiler mate)
3- Tankless/on-demand water heater
1- Tank style water heaters are the most popular type of water heater. They come in different sizes ranging from 3 gallon (point of use) to 100 gallon (commercial) capacities. They are available to utilize different fuels like natural gas, propane, and electricity. Electric water heaters can come with basic elements, or elements with refrigerant systems that utilize warm room air temperatures to save on monthly bills.
Their average life span is 8-10 years, but can be upgraded to last longer by adding or changing sacrificial anode rods (special metal rod installed in all tank style water heaters that sacrifices itself to protect the lining of the heater). Most of these units are very easy to work on and to replace. Temperatures can be turned up in these heaters, and mixing valves can be installed between the cold inlet and the hot outlet to temper the hot water if you are looking to achieve more hot water per hour. Industry standard 6 year warranty comes with most of these units with an available warranty upgrade to 10 years with anode rods kits sold separately by the manufacturer. In the event of a power outage, you will still have a full tank of hot water, and gas fueled chimney vented units require no power to run. As these types of units store hot water, and water expands as it is heated, in closed water supply systems which include check valves or pressure reducing valves, a thermal expansion tank needs to be installed to absorb the expansion created due to the water being heated. These are the least expensive types of water heaters, and can usually be swapped out within a few hours by a professional. The residential style unit can deliver between 15 and 25 more gallons than their capacity for their first hour of use with no mixing valve installed. Natural gas and propane units may recover their full capacity in less than one hour versus electric which may take up to two hours for full recovery. Most gas units utilize around 40,000 BTU’s per hour.
Pros of tank style water heater:
Simplest, fastest, and least expensive to repair and replace.
High reliability with very few controls.
Some don’t require electricity to operate.
Minimal expected problems during service lifetime.
Fastest delivery of hot water to fixture.
Cons of tank style water heater:
Tank can be run out of hot water.
Can have long recovery time if run out.
Shorter service lifetime.
Takes up floor space.
If no chimney is available, power-vented models are very expensive to replace.
Electric models cost more to operate than gas, and can take up to two hours for full recovery.
Are known to leak severely upon failure.
May require thermal expansion tank.
2- Indirect fired water heaters are utilized in conjunction with a boiler (steam or hot water baseboard heating system). Just like in a hot water baseboard system, the indirect fired water heater is another heating loop with a supply and return from the boiler. Some of these units come with a limited lifetime warranty, but BEWARE, most manufacturers will require you to produce invoices written by a licensed professional showing that there has been a yearly inspection of the anode rod to honor the warranty. Please consider the cost of the annual inspection of your anode rod, or request that your service tech check this while they come by for your annual boiler service (you must ask them to do this specifically). Almost all of these systems require a dirt and sediment filter, check valve, and thermal expansion tank installed to protect the unit. Many of these units also require mixing valves to temper the outgoing hot water to protect from scalding. These units have superior recovery and first hour delivery ratings. Most of these units boast a 200+ gallon delivery rate for their first one hour of use. This would be the ideal system if you’re looking to run more than one shower at the same time. These systems store hot water, so in the case of a power outage, you will still have a full tank of hot water. A properly installed and maintained system should last at least 10 years. The price to install or to swap this type of unit is significantly higher than a tank style water heater and requires a professional. If your heating system fails, you will be without hot water until it is repaired or replaced. As this type of unit doesn’t have its own burner, you will be running your boiler all year to produce hot water, which may be more expensive than a tank style water heater.
Pros of indirect-fired water heaters:
Highest gallon per hour delivery. Very highly unlikely to run out of hot water.
Best choice to run multiple showers at the same time.
Limited lifetime warranty on some units.
Stores a full tank of hot water in the event of a power outage.
Fastest water delivery to fixture.
Cons of indirect-fired water heaters:
Very expensive to install, and costly to replace if warranty is denied.
Requires a hot water boiler or a steam boiler to operate. May not be fuel efficient.
Has more controls that may fail than a tank water heater, but less than a tankless. Parts and labor are expensive.
If inner heating coil develops a leak, it can over pressurize your heating system causing havoc.
Most require documentation of yearly inspection of anode rod for warranty purposes.
May need to maintenance water filters to comply with manufacturer warranty (easy to replace).
Typically requires thermal expansion tank.
Takes up floor space.
Requires professional installation and swap.
3- Tankless water heaters are the newest style water heater on the market. Many people simply fall in love the idea of endless hot water, and the higher efficiencies that the top tier models can achieve. Many plumbers are in love with the money these things bring in, and they won’t tell you the ugly truth about them. I will though.
My number one complaint from a customer is “It takes so long for the water to get to my faucet!” Yes, because this unit does not store hot water like a tank style. First the unit must sense water flow (0.5 gpm) before it starts the exhaust fan. Then, the unit has to prove that the fan is running. Next, the gas valve opens and you have ignition. The computer inside then communicates with inlet and outlet temperature sensors and modulates the gas valve to heat the water to the set temperature appropriately in regard to the volume of water passing through. At this point, the water in your pipes starts to get hot, but it still has to push all that cold water out of the faucet before you can actually enjoy washing your hands. Make sense?
With all those controls and wires in mind, with most being critical to operation, what do you think the chances are that one of those controls will fail within the service lifetime? I wouldn’t bet against it. Some plumbers will refuse to work on a unit they didn’t install, some install then but won’t service them, and some just don’t know how to troubleshoot them. It’s literally spaghetti vomit with rainbow sauce. Keep that in mind.
Also, these units are designed with an expected temperature rise for a limited amount of gallons per minute depending on that temperature rise (delta t). The top tier units boast about 3.5 gallons per minute at a 70° temperature rise. So what happens in the northern climate when the water entering your house is 40° in wintertime? If the water leaving the unit is set at 110° it will keep up with the demand, but most folks like their water to be 120° or hotter. You must take into consideration how much heat your water is going to lose traveling from point A to point B as well (uninsulated pipes and cold spots). My favorite volume for a typical shower head is 2.5 gpm. Water saving heads just don’t have the power to wash that soap off as nicely as I’d like. Now open a kitchen faucet and add another 1.5 gpm to the demand… where’d the hot water go? And forget filling that tub with the faucet wide open. You will not achieve 5 gpm without a large capacity water heater before your tankless, or multiple tankless units. To me, that’s redundant.
Now let’s talk about scale. If you’ve ever seen the inside of a water line that has been cut out, you’ll notice that there is some substance stuck to the walls of the pipe. This is called scale. Scale can reduce the heat transfer through the piping in the combustion chamber, lowering the efficiency and performance of your tankless heater. Most manufacturers recommend a descaling of the unit once a year to keep it at peak performance (rough cost of $150-$200, but in my opinion, not necessary with good quality water). The amount of scaling that will occur depends on your domestic water quality.
Speaking of water quality, I’ve had warranty claims denied due to excessive hardness of water. The manufacturer of the unit insisted there needed to be a softner/water treatment system installed (more annual service, salt maintenance, and breakdowns) to get the water to a manufacturer specified acceptable level or hardness.
The top tier unit can utilize up to 200,000 BTU’s to keep up with the rapid heating demand these things require. It’s critical that the water lines and the gas lines are sized properly to ensure adequate performance.
Power went out? No hot water until it comes back on, and I hope that computer board didn’t get hit with a surge.
Venting typically requires 4 feet horizontally from any openable windows (unless using a concentric vent termination). You also need 4 feet from any air intake, other exhaust such as a dryer vent, or gas meter. You may see a large steam plume during colder months. If the neighbors complain, I hope you have it vented at least 10 feet from a lot line, because that’s code.
Some brands have very slow tech support. I waited over an hour for tech support to answer my call the last time I needed them. Personally, I wouldn’t want to pay a mechanical rate for someone to stand around for an hour.
These units are so efficient, they produce condensation (acidic byproduct of high efficiency combustion). In most cases, you’re going to need a pump to send it over to drain line. Also, it’s not a bad idea to install a condensate neutralizer if you have any metal drain lines. The acidic condensate can eat through the bottom of your cast iron or copper drain lines causing blockages and/or leaks, resulting in costly repairs if you don’t change the media out every year (not hard to replace).
Now… let’s get to the good part. These unit do perform amazing and it’s impossible to run them out if you stay within the GPM’s. High efficiency units may qualify you for a gas company rebate (they send you a sweet check in the mail). Many of these units come with a standard 15 year warranty on the heat exchanger, and 5 year warranty on parts AND reasonable labor (not as much as I charge for the labor, but it softens the blow a bit) if registered. They will save you space in your basement. Some units have the ability to recirculate hot water to the furthest fixture via wifi and an app on your cell phone (instant hot water!!). Swapping these units out (with the same exact model) is quick and easy, but still expensive if for some reason your warranty claim is denied. As a tank water heater will fire up a few times throughout the day, even when not in use, a tankless will save energy as it never fires to maintain temperature within the unit.
Pros of tankless water heaters:
They save you space.
They help the environment with higher efficiency models.
Gas company rebate with higher efficiency models.
Typically don’t require thermal expansion tanks.
Draw outside air for combustion.
Never run out of hot water (if within GPM’s).
Can come equipped with hot water recirculation kit.
Saves money when not in use.
Cons of tankless water heaters:
Long waits for hot water to arrive at the fixture (if non recirculating unit) and increased water bill.
Hot water can be interrupted when multiple fixtures are opened at the same time.
Recommended annual descaling and condensate neutralizer service.
Very high volume gas demand.
Complex electrical system. Some companies may refuse service if they didn’t install.
Expensive parts and labor if breakdown occurs.
Must be installed with properly sized and arranged gas, water lines, and vent.
Requires electricity to produce hot water.
As for electric tankless water heaters, don’t do it. You’ll regret it, and I’ll regret it. Trust me.
In summary:
The most powerful, yet maintenance critical (for warranty) unit is the indirect fired water heater. Limited lifetime warranty and highest gallons per hour delivery makes this system the king of water heaters.
Drawback is higher fuel consumption and wear and tear on your boiler.
The most complex, yet eco-friendly unit is the tankless water heater. Endless hot water is fantastic!
Main drawback is limited GPM and long wait times for hot water to arrive.
The most economical and reliable unit is the tank water heater. Unless you need more hot water than a tank can offer, this option is very hard to beat.
Service life expectancy is the biggest drawback, but can be extended with anode rod kit.
The questions are how many GPM’s are you trying to draw, and for how long? If it’s 2.5 or less gpm forever, then the tankless has your back. If it’s 5 gpm or more, you need an indirect fired tank (you’re going to run a tank style out in 10 minutes). If you are just running your water heater out of hot water, consider the least expensive alternative first: crank that sucker up to 160° and install a mixing valve. You’ll achieve (purely guessing ->) at least 30% more hot water. The mixer is compatible with any new water heater when it’s time to swap it out.
I hope this helps you to make the right decision for you and your family. Sorry I bashed the tankless so much. I firmly believe less controls = less problems.
For most situations, I would recommend a mixing valve first. If that doesn’t do the trick, I would recommend an indirect fired tank. I feel like fights might happen in your household over somebody opening a hot water faucet while somebody else is taking a shower. You wouldn’t believe how mad people can get over a little cold blast, or maybe they’d get used to it? Throwing a hot water faucet wide open might be a good way to make the teenagers take shorter showers 🤔 🤷🏻♂️
Thanks for reading. If you have any questions, or you think you’re ready for a bid, let me know.
-Mark Krasavage
Now I have to put that all in a chart form for quick reference, and because people don’t like to read 🤣
