How to Install A Tankless Water Heater

Now that you have selected your tankless water heater, the time has to come to install it in your home or office. Proper installation and maintenance of your water heater can optimize its energy efficiency.

Proper installation depends on many factors. These factors include fuel type, climate, local building code requirements, and safety issues, especially concerning the combustion of gas-fired water heaters. Therefore, it’s best to have a qualified plumbing and heating contractor install your demand water heater.

4 Factors to Consider When Hiring a Contractor to Install Your Tankless Water Heater:

  1. Request cost estimates in writing
  2. Ask for references
  3. Check the company with your local Better Business Bureau
  4. See if the company will obtain a local permit if necessary and understands local building codes, etc.

If you’re determined to install your water heater yourself, first consult the manufacturer. Manufacturers usually have the necessary installation and instruction manuals. Also, contact your city or town for information about obtaining a permit, if necessary, and about local water heater installation codes.

Tankless Water Heater Installation

Most tankless water heaters have a life expectancy of more than 20 years. They also have easily replaceable parts that extend their life by many more years. In contrast, storage water heaters last 10–15 years. Periodic water heater maintenance can significantly extend your water heater’s life and minimize loss of efficiency. Read your owner’s manual for specific maintenance recommendations.

  1. Indoor Gas Installation
  2. Electric Installation
  3. Outdoor Gas Installation

Indoor gas tankless water heater installation tends to be the most complicated due to the fact that the units must be vented. Depending on the location of the unit and the model selected you may vent be able to vent horizontally or vertically. Electric tankless units do not require any type of venting, however, they do require a substantial amount of electricity. We always recommend you discuss the electrical requirements with an electrician or professional installer before purchasing an electric unit. Outdoor gas tankless water heaters do not require venting, however, they do require a minimum amount of space around the unit.

Indoor Gas Installation

We always recommend consulting a professional installer or gas company in conjunction with the installation manual for each model before installing any gas tankless water heater. We provide installation manuals for all Bosch tankless water heaters we carry:

There are several important components to consider when installing a gas tankless water heater:

A. Do I have the correct gas connection coming into my house and do I have enough gas power to run the tankless water heater I purchase?
If you contact your local gas company or installation professional they can determine whether you have enough gas coming into your house to power a tankless water heater. You should print out one of the installation guides above as a reference for yourself and person installing the unit. We have provided a quick table below showing the BTU output by each model for each Bosch model we carry:

B. Do I have proper ventilation?
All gas tankless water heaters must vent the excess warm air they create. They can either vent vertically up through a chimney or roof pitch or horizontally through a side wall. Some units can only vent horizontally, some vertically, and some units can vent either way. You will want to know what options you have for venting before you make a decision on which gas tankless water heater may be right for you. We hav included pictures these venting methods below:

Components You Need to Consider

There are several components you will need to consider when installing a gas or liquid propane tankless water heater:

1. Vent Adapter and Stainless Steel exhaust hose
A vent adapter is required to attach the tankless water heater to the exhaust hose. You will need to select either a 3 inch adapter or 4 inch adapter depending on the model you select. All venting of gas or liquid propane tankless water heaters REQUIRES UL approved Stainless Steel vent pipes due to the heat produced in the venting process. Standard PVC piping is not recommended.

2. Vertical vs. Horizontal Installation
Gas or liquid propane tankless water heaters can be installed either vertically or horizontally. Some models can only be installed one way or the other so please read the product information listed on our site regarding the product to get a better understanding of how it can be installed.

  1. Horizontal Installation:
    There are two types of horizontal installation. With a downward slope installation you will need a vent adapter, 90 degree elbow, and an appropriate length of stainless steel vent hose to run the exhaust out of your side wall. You can then end the exhaust by using a wall thimble connecting the interior part of the vent with the exterior wall. You would then end the connection with a 90 degree elbow. With an upward slope vertical installation you will simply need to add a vertical condensate trap to your parts list.
  2. Vertical Gas Installation:
    Vertical installation of gas tankless water heaters can have more variables that the horizontal installation. However, the components necessary for the installation will remain the same. You will need a vent adapter, at least one 90 degree elbow, and condensate trap (condensate trap is only required for Rheem gas units. Bosch units have a built in condensate trap). You will need to buy enough stainless steel venting pipe to reach the exterior of your home. You will need a firestop for each ceiling the unit is vented through. Finally, you will need roof flashing, a storm collar, and either a 90 degree elbow or rain cap to terminate the installation.
  3. Combustion Air:
    Tankless water heaters require combustion air. It’s important to understand how combustion air will be delivered to your water heater and how much combustion air is needed. When placed in an unconfined area, combustion air can simply be the air within your home. Some of the tankless units we sell are meant to function in this type of environment where they do not pull fresh air from outside the room they are installed in. As a general rule of thumb any gas tankless water heater that uses internal combustion air musts have at least 10,000 cu. ft. of space around the unit. Confined areas (such as a closet) may require air ducts or additional air inlets. Models that require external combustion air require a second hose to be installed that pulls fresh air from outside of your home into the room you are installing the tankless water heater in. Check the installation manual for more information about combustion air requirements.

Electric Tankless Water Heater Installation

Many people that do not have the power needs for a gas tankless water heater or who cannot vent a gas model will opt for an electric model because they do not require any type of venting. Electric models, do however, require substantial energy requirements. Please consult the owner’s manual before installing an electric tankless water heater, or click here to view a comparison chart of all of the units we carry.

The size of your breaker box and how many amps you have available is the most important thing to consider when purchasing an electric water heater. Depending on which electric tankless water heater best fits your home needs, the required amps will be 150 or 200 amps. If you don’t meet the amperage requirements stated in the installation manual, how do you plan to adapt? Some home owners choose to add an additional breaker box to their existing wiring while others will replace their existing breaker boxes with bigger ones. Talk to an electrician or installer before taking the next step in buying an electric water heater to be sure you’ll be ready to put it to use in your home.

Outdoor Model Installation

Outdoor tankless water heaters may be a good alternative for you if you are not able to vent a traditional gas model. You will need to consult the owner’s manual of the outdoor model you are interested in to see what type of clearances are required for the outdoor installation.

Recommended Reading:

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Jeff Flowers

About Author

Jeff Flowers has been a self-described beer geek for over a decade now. When he's not chasing his daughter around, you can usually find him drinking a fresh brew and wasting too much of his time on both Google+ & Twitter.

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