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T-K4-OS Outdoor Tankless Water Heater

By Takagi

Add a tankless water heater to your home and enjoy never running out of hot water, always knowing that there will be enough hot water for every shower, bath, or other use. These units are designed for outdoor installation, but will still take up far less space without that bulky holding tank, and is powerful enough for up to three bathrooms. Let PlumbingSupply.com® be your source for Takagi products.

We also offer many more tankless water heaters by Takagi:
to T-KJr2-IN - to T-KJr2-OS - to T-K4-IN - to T-D2-IN - to T-D2-OS

Takagi T-K4-OS - Tankless Gas Water Heater For Outdoor Installations

Takagi's T-K4-OS is a small, yet powerful tankless water heater which is designed to handle heavy residential use (or light commercial needs), and be installed outside mounted on an exterior wall. As it is installed outside, you will see a huge savings on the costs for the stainless steel venting required for any indoor heaters. This water heater is only 20.5" x 13.8" x 8.5", so it will save space for those looking to maximize storage space in your home and garage.

Takagi is the leader in tankless water heaters and the T-K4 can significantly reduce your heating bills, again saving you money. It will take the place of your common 50 to 80 gallon, old tank-style, water heater - simplifying your maintenance. There's no pilot light to waste gas and the heater itself turns on (by electronic ignition) only when it senses a very low .75GPM (gallons per minute), so this will prevent hot water loss from leaky fixtures and faucets, but will be enough so you can get hot water to your bathroom sink for hand washing.

The bottom line is that the Takagi T-K4-OS can save costs and labor on install, free up space, reduce your monthly bills, and make your life more efficient. Of course with newer technology there is a need to learn it as well. Tankless water heaters will not stop heating the water until the flow stops. So if you decide to take an hour-long shower, you can, but keep in mind that you are no longer saving money on your energy bills, or water costs. Teaching your family how tankless water heaters work is key.

View more detailed specifications
View flow rate and pressure loss information
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Takagi T-K4-OS Water Heaters

Model # Description Price & Quantity
T-K4-OS-NG Tankless Water Heater - Natural Gas $729.34 Enter a quantity and
T-K4-OS-LPG Tankless Water Heater - Propane $729.25 Enter a quantity and

Note: Wall brackets are built onto the T-K4-OS and do not need to be purchased separately

Installation Kit

Description Price & Quantity
Package includes: $205.81 Enter a quantity and

Please note: some areas do not allow installation of a few of these water heaters. Read more


View a Takagi tankless water heater comparison chart


Accessories for Takagi T-K4-OS Tankless Water Heaters

Temperature Remote Controller

Image Description Price & Quantity
Temperature remote controller Temperature Remote Controller
  • This allows the output temperature to be adjusted beyond the factory settings, and works as a diagnostic tool for error codes.
$103.30 Enter a quantity and

Wall Mount Drain Pan

Image Description Price & Quantity
Wall Saver for Tankless Water Heaters Drain Pan with PVC Adapter
  • Designed to help protect areas around the mounted heater from water damage.
$52.49
6-pack of Drain Pans - includes PVC drain adapter $283.44 Enter a quantity and
PVC drain connector Replacement PVC Drain Connector
Includes 1 each: 1" PVC male adapter, gasket, and locknut
$5.57 Enter a quantity and

Order 6, 12, 24 or more drain pans for additional savings!
Order 2, 4 or more 6-Packs for additional savings!

Pricing discounts will show up in your shopping cart.

Brass Pressure Relief Valves

Image Description Size Price & Quantity
Pressure relief valve Brass Pressure Relief Valve
  • A pressure relief valve is required for all tankless water heaters. In some areas, a temperature and pressure relief valve is required. Check your local plumbing code for more information
3/4" FIPS x 3/4" MIPS $14.67 Enter a quantity and

Brass Temperature & Pressure Relief Valves

Image Description Size Material Price & Quantity
Pressure and temperature relief valve Brass Temperature and Pressure Relief Valve 3/4" FIPS x 3/4" MIPS FOR Potable Water $59.65 Enter a quantity and
3/4" FIPS x 3/4" MIPS NOT FOR Potable Water $13.95 Enter a quantity and

"The Isolator" Isolation Valves

Image Description Size Price & Quantity
Isolation valve set Isolation Valve - Set   (Hot & Cold) 
  • Includes pressure relief valve. Complete inlet/outlet valve system that provides everything you need for a secure installation including full port testing and flushing of the system with easy to install union connections. Includes pressure relief valve.
    2014 Federal Safe Drinking Water Act compliant
3/4" FIP Union x 3/4" FIP $99.62 Enter a quantity and
Isolation valve set Isolation Valve - Set   (Hot & Cold)  
  • Includes pressure relief valve. Complete inlet/outlet valve system that provides everything you need for a secure installation including full port testing and flushing of the system with easy to install union connections. Includes pressure relief valve.
    2014 Federal Safe Drinking Water Act compliant
3/4" FIP Union x 3/4" Sweat $99.42 Enter a quantity and

Gas Connectors

Image Description Size Price & Quantity
Stainless gasflex Stainless Gasflex 1" OD (3/4" ID) x 24"
with adapter to 3/4" FIP x 3/4" MIP
$35.44 Enter a quantity and
Gas ball valve Gas Ball Valve 3/4" $8.28 Enter a quantity and

Ball Valves

Image Description Size Price & Quantity
3/4inch ball valve FIP Ball Valve   3/4" FIP $13.64 Enter a quantity and
3/4inch ball valve sweat Ball Valve   3/4" Sweat $13.65 Enter a quantity and
Stainless steel nipple adapter Stainless Steel Nipple Adapter 3/4" MIP x 1-1/2" Long $3.97 Enter a quantity and
 Order 10, 50, 100 or more of the same item for additional savings!
Pricing discounts will show up in your shopping cart.

Flexible Corrugated Water Flexes

Image Description Material Size Length Price & Quantity
Stainless steel water heater flexes Flexible Corrugated Water Flex Stainless Steel 3/4" FIP x 3/4" FIP 18" $7.44
3/4" FIP x 3/4" FIP 24" $8.27 Enter a quantity and
Copper / Stainless Steel 3/4" FIP x 3/4" Nominal Sweat 18" $7.61
3/4" FIP x 3/4" Nominal Sweat 24" $8.34 Enter a quantity and

FloodStop Systems for Water Heaters

Features:
  • Easily prevent water damage from a leaking water heater with this unique device
  • The unit automatically shuts off water supply to the water heater and sounds an alarm leaving all other household fixtures and appliances operational
  • Provides additional protection by requiring AA batteries to be inserted to protect in case of a power outage (batteries not included)
  • Controller will operate normally without batetries installed but will continue to beep until they are inserted
  • Can easily be installed in fifteen muinutes
  • Full-port motorized ball valve (brass)
  • 2014 Federal Safe Drinking Water Act compliant
FloodStop Components:
  • Motorized Full-Port Ball Valve (3/4 inch NPT pipe threaded)
  • New Style Control Unit (with Battery Backup 4 X AA Size)
  • Water/Leak Sensor (1-1/4" X 7-1/2")
  • AC Power Adaptor (or use 4 X AA Batteries as Primary Power Source)
  • Output Contact Wires (2)

Model # Description Price & Quantity
FS 3/4-NPT-V4 Water Heater FloodStop System - 3/4" Pipe Threaded
Works with any 3/4" MIPT supply line - rated 0-180 psi
$149.95 Enter a quantity and
FS 3/4-C-V4 Water Heater FloodStop System - 3/4" Compression
Works with any 3/4" copper applications - rated 0-180 psi
$166.49 Enter a quantity and

Make sure to follow all of the manufacturer's instructions and directions by performing the proper maintenance and inspections
to ensure that you are fully protected from flooding - this is ever-so-important with (man-made) safety devices as they will eventually fail.


Related Items & Accessories



Please note: For potential safety reasons, we do not recommend using PVC to vent gas tankless water heaters. For the best results, we recommend using Category 3 stainless steel gas vent pipe for all gas tankless water heaters.



Common Terms and Definitions
  • C, SWT, or Socket: A regular hub or socket. The pipe fits (sweats/solders) inside this
  • Mips: Male pipe threads on the outside of fitting
  • Fips: Female pipe threads on the inside of fitting
  • FTG: The same size as the pipe. Will fit inside a socket (hub) fitting
  • Hyset: Has a nailing flange on the front of the fitting
  • Dropear: Has a nailing flange on the back of the fitting
  • Nominal: Used to describe copper pipe and fittings in plumbing. Refers to the inside diameter of the pipe which varies by thickness of the pipe. The outside is a constant size and is always 1/8" larger than the nominal size. Example: 1/2" nominal is always 5/8" O.D.



Frequently Asked Questions

Q. "There are many companies selling all kinds of tankless water heaters. Why should I buy a Takagi tankless gas water heater from you rather than elsewhere?"
A. We are a large, reputable company that was here yesterday and we will be here tomorrow. We are often copied, but we don't believe that any one can match our service and certainly our base of satisfied customers is larger than any Internet plumbing supplier since 1995. We sell 1000's of other quality plumbing products as well, so you can rest assured that we know plumbing products. We are a very stable and reputable company. We love to sell what we believe in, and we definitely believe in Takagi.

Q. "If these units don't have a tank, how do they know when to turn on?"
A. These tankless water heaters have a flow switch built into them. When you turn on the hot side of a faucet the water begins moving. Once the water is traveling at minimum flow rate for the heater, the flow switch will turn on the gas.

Q. "I've heard that some Takagi tankless water heaters cannot be installed in a few areas. Is that true?"
A. Yes, there are some counties that do not allow for the installation of a few Takagi tankless water heaters. For this reason, the person purchasing one of the following models is responsible for checking with their local code authorities prior to ordering: T-M32-NG, T-D2-IN-NG, T-D2-OS-NG, T-K4-IN-NG, T-K4-OS-NG, T-KJr-IN-NG, T-KJr-OS-NG. Here's a list (not complete) of some California counties that do not allow these water heaters to be installed: Sacramento, Yolo, Sonoma, San Joaquin, Napa, Marin, Solano, Contra Costa, San Francisco, San Mateo, Alameda, and Santa Clara. Again, this list is not complete, so it's up to the purchaser to check with local code authorities prior to ordering.

Q. "Why can't I install the T-K4-OS myself?"
A. Improper installation of the T-K4-OS could create carbon monoxide gas and other dangerous gases. Installation of this unit by persons other than professionally trained technicians voids the warranty.

Q. "What's the first hour rating of this water heater?"
A. Traditional tank water heaters have a first hour rating which is determined by the amount of hot water the heater can produce in an hour when starting with a full tank of hot water. As tankless water heaters do not start with a tank of hot water, they don't really have a first hour rating the same way a tank water heater does. Instead, tankless water heaters have a gallons per hour rating, which is determined by how many gallons per hour the tankless water heater can produce when raising the incoming water temperature a specified amount.

Q. "I live in an area where it freezes, what can I do to protect the heater from freezing?"
A. We recommend you use the TK-BF01 exhaust back flow prevention kit to prevent cold air from entering the vent and causing the heat exchanger to freeze.

Q. "Will an instantaneous water heater save me money on my utility bills?"
A. In many applications you can see a savings. There are some variables that could reduce the amount you save. One example is you will not run out of hot water, so longer showers could cut into your savings. Also, the cost of electricity, propane and natural gas in your area will affect the amount of money saved. The higher the cost for the energy type used to heat your water, the quicker you can recover the higher initial cost of installing a tankless versus tank style water heater.

Positives:
  • You will never run out of hot water. "You want an hour long shower? No problem!"
  • Electric units can be installed at the point of use.
  • You're not paying energy costs to heat water 24 hours a day.
  • Our electric units don't require a T&P valve (no tank!) - if code allows.
  • Installing a tankless water heater can indeed be a bonus to the environment. (Why choose wastefulness when we're talking about finite natural resources?)
Negatives:
  • They all need a minimum flow rate & pressure to turn on.
  • Electric units need heavy gauge wire, while gas units need a much larger, special flue pipe and larger gas supply than a conventional water heater.
  • At times they can produce very hot water. It's easier to get scalded - but this is easily mitigated with anti-scald valves.
  • With some brands, parts are hard to find (not a negative if you originally purchase from us, as we like to carry parts for the units that we sell).
Summary:
Tankless water heaters have their place. They're not "the answer" to every hot water need, but if they're used correctly they can be the solution to many of them.

Q. "Your products specify the 'temp. rise' based on the GPM flow; what do you mean by this?"
A. Temperature rise is the amount the heater raises the temperature of the incoming water, based on the flow rate shown of that water.

Q. "It sometimes drops below freezing where I live. Can I still install a Takagi tankless water heater outside?"
A. Takagi gas tankless water heaters are designed to be installed outdoors only in mild temperate climates. The factory-installed freeze protection device is rated for temperatures down to 5°F in a wind-free environment, so wind-chill factors must be taken into account when choosing whether or not to install a Takagi tankless water heater outdoors. If you are unsure if temperatures at your planned installation would work for an outdoor tankless water heater, we strongly recommend consulting with a trusted local professional.

Q. "What do I need to install these Takagi tankless water heaters outdoors?"
A. Outdoor-only Takagi tankless water heaters, such as the T-D2-OS or the T-K4-OS, require no additional venting components. Units that can be installed either indoors or outdoors, are designed to need only the addition of an outdoor vent cap or properly vented recess box in order to function in an outdoor installation. Please note that Takagi tankless water heaters, like most brands of water heaters, are designed to be installed outdoors only in mild temperate climates. As always, please consult with your installer or another trusted professional before installation.

Q. "What are the best reasons to install a Scale Inhibitor System?"
A. The system inhibits scale build-up and protects the piping from corrosion, which helps maintain efficiency and extends the life of the system.

Q. "How does the Water Heater Scale Inhibitor System prevent corrosion?"
A. It forms a thin protective layer on the inside of pipes and metal parts. This film or layer is microscopic in thickness and will not build up over time.

Q. "What happens if you don't change cartridges often enough on the Scale Inhibitor System?"
A. The original water condition and problem will reappear. Hardness will begin to build up again, which you want to avoid.

Q. "What is siliphos?"
A. Siliphos is a water treatment compound; a glass-like Polyphosphate containing Sodium, Calcium Magnesium and Silicate, formulated specifically for the treatment of water problems and to prevent the build-up of scale in plumbing. It is made from a blend of food grade organic phosphates, and has been approved by the USDA for drinking water and all food applications. It is safe for ingestion by humans, animals, and plants, and does not build up in waste water.

Q. "Is the Water Heater Scale Inhibitor System's active ingredient safe?"
A. Yes! All ingredients used are 100% pure food grade materials. They are approved by the USDA and meet purity requirements as a food additive by the World Health Organization.

Q. "Will the Water Heater Scale Inhibitor System change the taste or odor of water?"
A. No. The active ingredient is colorless, tasteless, and odorless when used as recommended.

All Takagi tankless water heaters must be installed by a licensed professional.


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