Tankless Water Heater Guide - What You Should Know about Gas Tankless Water Heaters
Tankless Water Heater Guide - What You Should Know about Gas Tankless Water Heaters

Gas Tankless Water Heaters | What You Should Know

By Mike Holmes

Mike’s Advice / Home Renovation

Monday, November 1st, 2021 @ 5:15pm

Tankless Water Heater Buying Guide  

Are you sick of running out of hot water? You may want to consider a tankless water heater. There are a lot of benefits of going tankless, but one of the biggest benefits is continuous hot water. In this article, I am going to give you the information you need to make a decision about buying a gas tankless water heater.

Heating water is the average home’s second-highest utility cost after heating and cooling the house itself. A tankless (or on-demand) hot water heater is different from a typical water heater because it produces hot water ON DEMAND. The units run on electricity, natural gas, or propane.

Here’s what you need to know about picking and installing a tankless water heater.


What Is A Tankless Water Heater?

With a regular water heater, when you turn on your hot water tap, it draws water that has already been heated (in the tank). With a tankless water heater, the water is pulled fresh from the source and is quickly heated on its way to the hot water tap. Because of this, you will never run out of hot water. Continuous supply of hot water!

Mike Holmes and Bosch Tankless Water Heater

Bosch Tankless Water Heater Installed On One Of Our Projects.

Are Tankless Water Heaters Better than Storage Tank Water Heaters?

If you have a tankless water heater and you are out all day, you will not be heating water that you won’t be using immediately. With water heaters with storage tanks, you are paying to have hot water whether you need it or not. 

Tankless water heaters are highly efficient because they only heat water when needed. Also, a good idea if space is limited. Some models are quite slick.

Electric vs Gas Tankless Water Heater

If you are considering an electric tankless water heater, keep in mind that you may have to upgrade the electrical service to your house. Many manufacturers require installation by factory-trained professionals to maintain the warranty.

Gas water heaters are less expensive to operate, due to the lower cost of natural gas. If you live in an area where electricity rates are high, your electric tankless water heater will be more costly to operate. Gas-fired tankless water heaters produce higher flow rates than electric ones.

It is important to compare fuel costs as you are making a decision.

How Does a Gas Tankless Water Heater Work?

When you open your hot water tap or start your dishwasher or washing machine on a hot cycle, your unit will recognize the need for hot water and the heating process starts. Instant hot water!

This involves drawing air from the outside, opening the gas valve that lets in the gas, and igniting the burner. The unit will assess the temperature of the incoming water and calculate how much heat the burners must produce to deliver the water at the temperature you want.

The condensing unit works this way:

  • Flame ignites and heats two heat exchangers
  • Secondary heat exchanger preheats the water by reusing the heat going up the fuel pipe 
  • The primary heat exchanger continues to heat the water
  • Water travels to where the hot water is needed
  • Flame output adjusts to maintain the desired temperature
  • When hot water is no longer needed, the unit will shut down (stops energy usage) and wait until the next time you need it.


Bosch Gas Tankless Water Heater

Because your hot water heater is your home’s most important appliance, it’s important to go with a trusted brand and hire the right professionals to have it installed. I don’t recommend installing a water heater yourself.

The manufacturer I recommend for gas tankless water heaters is Bosch – I just had one of their units installed on my latest project. It looks slick because of the design, but it’s the technology and what’s inside that matters.

A Bosch Greentherm 9000 arriving at our warehouse for one of our homeowners!


Your Bosch Tankless Water Heater has ultra-efficient condensing technology. Indoor models can be converted from natural gas to liquid propane, and flexible venting options keep installation simple.


How To Choose A Tankless Water Heater?

There are many factors to consider when it comes to choosing a tankless water heater, including the size of your home, your water usage, and even electricity costs if you’re considering getting an electric tankless water heater. Some cities also offer tax rebate programs, so this might be another factor to influence your decision.

Product features and innovation is other important factor to consider when comparing different models. I personally love the Bosch Greentherm 9000, and here are some benefits of installing this system:

A Bosch Greentherm 9000 has many benefits for homeowners and contractors.


Human Machine Interface (HMI)

The digital touchscreen in the front represents the product dashboard. It displays the heat exchanger temperature, the incoming water temperature, and MOST importantly, the outlet water temperature. No other manufacturer has this.


When it’s time to do maintenance checks, your technician can use the digital HMI to access operational data about the performance of the unit, including inlet water temperature, outlet water temperature, heat exchanger temperature, fuel gas temperature, air pressure, water flow rate and much more!

UEF Rating (Uniform Energy Factor)

I want you to look at the UEF rating for the manufacturers you are considering. A water heater’s UEF rating is a measure of its energy efficiency. The higher the number, the more efficient the unit is. Water heaters with high UEF ratings will yield a higher return on every dollar of energy you put in.

The Greentherm 9000 offers an efficiency rating of UEF up to 0.96 (or 96 cents on the dollar).

Wi-fi Technology


Gas tankless units that come with digital functionality are great. They let you adjust the temperature and monitor gas and hot-water usage on your phone. That’s why I love the Greentherm 9000 series. You can also remotely activate the recirculation pump straight from your phone.

RELATED: Understanding Heat Pumps and Boilers


What I Love About the Bosch Tankless Water Heaters

  • It LOOKS slick, but we know what’s inside the box that matters.
  • Topwater connections make it quick and easy to replace an existing storage tank water heater
  • Increased functionality with the app. You can remotely control the water temperature.
  • Your Bosch Greentherm 9000 series unit will also come with bottom drain ports (no need for expensive isolation ball valves). This is also great for the long-term effectiveness and durability of the unit. You can do descaling without any external valving.

How Long Do Tankless Water Heaters Last?

If you take care of your unit and do the preventative maintenance recommended by your manufacturer, it should last you about 20 years. This is two to three times longer than tank-type heaters. The Bosch Greentherm 9000 comes with an industry-leading 15-year warranty on the heat exchanger. 


Nine Jobs to Leave to the Professionals


Tankless Water Heater Installation

This is best left to the pros. I do not recommend attempting the installation yourself. Gas tankless water heaters require a gas line, adequate combustion air, a vent to remove combustion gas, and an electrical outlet to power the unit. 

For the burner in a tankless heater to perform properly, it has to be hooked up to a gas supply line that delivers enough volume at sufficient pressure. You don’t want to be messing around with this stuff on your own. 

This can be a potentially dangerous task, so bring in the right professional. Before hiring a contractor, review their proposal and quote. They should include every detail about the job. If they’re vague, move on.


Gas tankless water heaters need to be piped directly to the outside. You also need to make sure your vent location follows your local code regulations. 


For my contractor friends out there, the Greentherm 9000 is easy to install.




What Size Tankless Water Heater Do You Need 

Size does matter when it comes to choosing a tankless water heater, that’s why it’s important to work with a professional. If you install one that’s too small, you will not have adequate hot water. If you buy one that’s too big, you are carrying extra costs. Think about your needs and your lifestyle, to find the right size to meet your home’s hot water demand. To determine what on-demand water heater is right for you, you need to estimate the flow rate, the temperature rise, and the heater’s efficiency.

The flow rate (GPM – gallons per minute) is how much hot water you will need at any given time and temperature rise is the difference between the incoming cold-water temperature and the desired temperature and the heater’s efficiency is indicated by the Uniform Energy Factor (UEF).


When determining the appropriate unit, you want to know how many fixtures you want to run simultaneously. A tankless water heater will control the flow of water entering the unit to ensure that the unit is always producing water at the set temperature. If you exceed the capacity of the unit, you will get a reduced flow rate but the temperature will remain at the set temperature.

The Greentherm 9000 with a 199,000 BTU heater is designed for residential applications and can deliver hot water up to 140 degrees F (60C) with an 11.2 GPM flow rate at a 35 degree F (1.6C) temperature rise and can produce enough hot water for 2-3 major appliances in most homes.


Hard Water and Maintenance for Tankless Water Heater

This is a good time to get your water professionally tested for water quality issues. If there is scale buildup in your drains and pipes, or your showerhead aerators for faucets are becoming clogged, the water flow rate will reduce.

Follow your manufacturer’s instructions on preventative maintenance that you need to do on the unit. If you have hard water (like I used to), you should be removing hard-water deposits and cleaning out the sediment filter on the unit. 

I had my water tested (after losing a water heater to scale) and I was surprised by what they found. Turns out I needed to install a whole home water filtration system, and I used the pros at Kinetico Water Systems for my own house. 



Time To Replace Your Tanked Water Heater?

If your storage tank water heater is due for a replacement, I would strongly recommend looking into tankless water heaters. The upfront costs for tankless water heaters will likely be higher, but that’s when you need to start looking at rebates offered in your area. Your tankless water heaters will last longer and have lower operating and energy costs than a water heater with a tank, which also offsets the higher purchase price.




Bosch tankless water heaters are some of the best in the industry, and with seven Greentherm 9000 models to choose from you know you’ll find the perfect unit for your home’s needs. With an average lifespan of 20 years, more than double that of the tank version, and backed by one of the best industry warranties in its class, Bosch gas tankless water heaters are a practical, easy way to upgrade your home.



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