Review of Tankless Water Heaters

A review of tankless water heaters to help you decide the best one for you.

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Table of Contents

I’m not sure if you noticed but we are quickly running out of resources on this fabulous earth. For that reason alone, I wanted to look into a tankless water heater. The other reason? I’m cheap and I don’t want to pay any more money than I have to for my energy.

I had always heard that you should only use a tankless water heater if you were going to use gas and then I saw this Rinnai electric unit when I was on the Tour of Homes (see other fabulous photos from those tours here) and I thought I should rethink this.

rinnai water heater

Sadly, I couldn’t find a ton of information. I found an article from This Old House and one from Home but everything else was too technical or from brand sites…and I have a healthy skepticism of brands pushing their product untruthfully. There is a good overview of tankless water heaters from Happy DIY Home if you find that you need a different “voice” to understand the information.

Tankless vs Standard

Looking at how a tankless water heater works, they are a LOT more efficient. Basically, a standard water heater holds X gallons (a normal amount is 40 gallons) and then it was a metal rod inside that keeps it at a heated temperature all the time. That water heater is heating water 24/7/365 whether you are using it or not. And, there’s a limit. When the hot water that is already heated is gone, the tank refills and it gets heated up again.

A tankless water heater…has no tank. As water goes into the water heater, it is sensed by a flow sensor which signals the control panel to turn on either the gas or electricity to heat the coils inside. Water flows through the heated coils and comes out hot on the other side.

Tankless is safer since there is no tank to flood your home with 40 gallons of water when you’re on vacation. It’s more efficient since it isn’t heating the water until you need it. Tankless water heaters are also easier on your electrical bills and typically you get tax breaks. AND (I know, how could there be more?) tankless water heaters are smaller, which I love.

Needless to say, I am all in on the benefits of tankless. Now, I needed help deciding what I wanted.

Electric vs Gas

Electric water heaters are not able to heat as much water to as high a temperature as gas. However, there are tons of people trying to downsize and these units are PERFECT for tiny homes or even people who live alone since they won’t tax the system as much. Electric water heaters are slightly more accessible though because not every home has gas lines.

If you are a person who likes to multitask and do laundry while taking a long hot shower, you will probably want a gas water heater, at least with today’s technology. Gas water heaters, while they do cost more, also last longer.

I’ll be honest, I like to multi task and I like long, hot showers so I clearly need a gas water heater. What size though?

Calculating the Size


There are some incredibly complicated calculations that you can use to determine what size tankless water heater you need.

First, you need to calculate the maximum gallons/minute that will be demanded of your water heater. So, when you have everything (shower, dishwasher, etc) turned on that is using hot water, how many gallons are flowing per minute. You multiply this by .8.

Second, you need to figure out how many BTUs per gallon you need. This depends on how cold your ground water is, which is determined by where you live. It basically is how much heat it takes to heat your water up to useable temperature. Fun fact, this is also how calories function 🙂

Third, multiply by 60 minutes.

Finally, multiply by the Uniform Energy Factor (UEF) of the water heater, which should be listed on the water heater.

Water Heater Size

I don’t know about you…WHAT?

So, rule of thumb is:

Single person/One bathroom/Low demand requires 150,000 BTUs

Small family/Two bathrooms/Moderate demand requires 200,000 BTUs

Large family/Multiple bathrooms/High demand requires 400,000 BTUs

If your situation moves you to the next level up in demand in 2 out of 3 categories, just size up and play it safe. You only want to install the water heater once.

Paying for it

Okay, so I’ve decided to go ahead with a tankless water heater and I’ve determined a size and type, now I was wondering how much they cost.

On demand units are the least expensive, somewhere around $800 for an electric one depending on your market.

Electric ones, depending on the BTUs and some key features, like connection with your phone, you should expect somewhere between $1000 and $2000.

Gas water heaters, again depending on unique features and your market demand anywhere between $1500 and $3000.


I will one day soon, be purchasing and installing a tankless water heater in my home because of everything they offer. Sure, they cost more but the energy savings, space savings, and safety features are worth the added cost.

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Head Homeowner

Hey everybody! I'm Sydney, the head homeowner here. Let me know if you have any questions you didn't find the answer to. Tell me what projects you're working on. I love to hear from all my readers.