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New To Tankless?

Introduction to Tankless Water Heaters

Table Of Contents

Introduction to Tankless Water Heaters

This is a new technology for many people, but amazingly this technology has been around for a long time. The products have been produced and improved for several years resulting in the most efficient and cost effective way to heat water.

Radiant Heating vs. Domestic Use

Many people look into tankless water heaters for use with radiant heating systems. A radiant heating system runs hot water through a radiator in a room or pipes in a floor to effectively heat the house. Tankless water heaters are not designed for this use. There are some units with modifications that can be used for this purpose, but in most cases the safest implementation of a heater for a radiant heating system is a boiler. If you plan on using a tankless water heater for a radiant heating system you could void your warranty or destroy your heater far earlier than the expected life of the unit. Please call us and ask if you have questions concerning this, there may be some alternatives that we can consider.

What Type of Water Heater?

Some people are limited to gas appliances because they do not have electricity. Others prefer to use an all-electric unit so they do not need a gas supply.

Many of the newer units are using a mixture of gas and electricity. The heaters are using the gas to heat the water, and the electricity for electronic spark ignition, freeze protection, combustion air fan, and operating controls. As the water heaters are advancing we are seeing more electronic components incorporated in their design, such as sensors and fans, thus more units are requiring electricity.

What if I do not have electricity?

We have some gas tankless water heaters that run entirely on gas (both propane and natural gas) and require no electricity. It is important to select the correct water heater, as many of them say gas, but they still require electricity for the electric spark ignition and electrical components.

Gas Units (these units use gas exclusively, no electricity):

I want a unit that runs entirely on electricity!

We have units that do run entirely on electricity. These are excellent water heaters with a lot of technology built into them, but there is a very important thing that you must remember when you want to run a heater completely off of electricity. Can your current service handle it? An electric water heater must generate a lot of heat to raise the temperature of the water as it passes by! This process uses a lot of amperage. When you are picking out an electric water heater you should check your total amperage of your electric service and see if you can accommodate the additional amps required by a tankless electric water heater. For example, if you have a 100 amp service and you are going to buy a 80 amp water heater, then you will only leave yourself with 20 amps for the rest of the house, when the water heater is on full. It is important that you know how much current the rest of the house needs, and that you read the instruction manual about your water heater so you know how much current that unit uses. Then you must ensure that your electric service will be large enough to provide for all of the uses. The electric units require dedicated lines from the breaker box all the way to the heater, they often times use smaller gauge (larger wire) then is used in the rest of the house. They also require their own breakers. Many people will run the units on 240VAC instead of 120VAC. It is possible to install 3-phase units as well, but this would be more for large scale installations or for commercial applications. Most people think they have 3-phase running to their houses, but in reality it is almost always single phase. Please call us or your electrician if you have any questions about tankless electric water heaters.

Electric Models:

Indoors vs. Outdoors

Outdoor tankless water heaters are convenient because they require no venting, but many of us live in climates where the temperatures sometimes reach below freezing. Many tankless water heaters say that they have freeze protection, and in-fact most of them do. The problem comes with the piping, there is no freeze protection installed on exposed pipes that feed an outdoor unit. Thus, if you are in an area where you receive below freezing temperatures, then an outdoor model is generally not for you.

Considerations for Outdoor Units:

Even though an outdoor model does not require the consideration of venting, it does require that we pay attention to where the exhaust goes. On all outdoor gas models the exhaust could blow back into the house if installed next to a window or a door. There are a lot of different clearances declared in the manuals for each water heater. It is important that you read and adhere to all of the clearances specified in the manual. It is also important that you follow any local codes that could apply to the installation.

Outdoor Models:

Considerations for Indoor Units:

Indoor gas units require proper venting of the exhaust gases. There are two categories of indoor gas units, they are fan assisted and atmospheric. Fan assisted tankless water heaters can be vented vertically through a roof or horizontally through a wall. Atmospheric gas tankless water heaters allow only vertical venting without after market equipment.


Naturally aspirated units use the oxygen in the air for the flame to burn and the exhaust is emited from the dwelling via a vent flue. For these units you can use general venting that is installed in most houses such as B-vent. It is important that the venting size be correct. If you have a flue that feeds into a common vent for all of your appliances then make sure that it is large enough to accommodate the water heater and all other appliances.

Atmospheric Models:

Fan Assisted:

Fan assisted unit's use the oxygen in the air for the flame to burn and the exhaust is forced out using a fan. For these units you must use special venting specified in each units manual. For almost all fan assisted units you must use a Category III stainless steel that is sealed. This venting can get expensive if venting over a large distance. It is strongly recommended that you try and terminate the vent as soon as possible when using a fan assisted unit. Fan assisted models draw larger amounts of oxygen from the air thus they require more air to opperate.

Some people install the unit in a closet or confined space, not giving the unit a lot of air. If you wish to do an install in an area like this then you need a Direct Vent model. You do not need a Direct Vent model if you can give the room that the water is installed in, 1 square inch of access to house hold air for every 1,000 BTU, or 1 square inch of access to fresh (from outside) air for every 4,000BTU. For example if you are looking at a 200,000 BTU unit and you have an open area to the rest of the house that is 200 square inches, or you have an area open to the outside that is 50 square inches then you would not need a Direct Vent model. If you had a 200,000 BTU unit installed in an area where house hold air could only pass through a 100 square inch area to reach the water heater, then this would not be enough (200 sq in would be), then you would need a Direct Vent model.

Fan Assisted Models:

Direct Vent:

Direct vent models use a venting system that circulates air from outside the home. The heater itself has a sealed cover and does not use any air from the room where it is installed. Two pipes run from the water heater through the roof or wall of the home, one for exhaust, one for fresh air intake. This is acheived using either concentric piping (a pipe within a pipe) from the heater to the outside, or using two individual pipes with a concentric pipe termination through the wall or roof depending on the model. Please click here to see a diagram of a direct vent system.

Fan Assisted Direct Vent Models:

How big does the capacity of the water heater need to be?

Tankless water heaters are classified by their rated input expressed in BTU/hour. BTU stands for British Thermal Units which is a way of measuring energy. The higher the BTU rating the more water the water heater can heat, or the hotter it can get the water. The best place to start understanding how to gauge the "capacity" of a tankless water heater is by the units in which it is measured. A tankless water heater is said to raise the temperature of water a certain amount of degrees per flow rate. For example the Paloma PH-28RIFS can raise the temperature of the water 45ºF at 7.4gpm.

The 7.4gpm means a flow rate of 7.4 gallons per minute. To put this in perspective, a sink uses about 1gpm, and a shower about 2.5gpm. If we want the water in our house to get to 120ºF so it will be really hot for the dishes and laundry, and we know that we have 50ºF ground water coming into the house, then we know that we need a 70ºF rise in the temperature of the water (120ºF - 50ºF). From looking at the information on the PH-28RIFS web page we see that there is a 4.8gpm flow rate at a 70ºF rise, well that is what we want is a 70ºF rise. In order to maintain the water temperature through out the house we should not exceed a flow rate of 4.8gpm approximately 2 showers. If we want to use more the 4.8gpm (2 showers) and keep the temperature at 120ºF then we need to look at different units, or the possibility of putting multiple units together.

When we say raise the temperature of water 45º we mean raise the temperature of the water 45º above what it is coming in at. Because we are raising the temperature of the water it is very important that we consider the temperature of the ground water when it comes into our home. Let's say that we are using the PH-28RIFS, at 7.4gpm. This means we have the equivalent of 3 showers going at this exact point in time. At this flow rate (7.4gpm) we can get a 45ºF rise in the temperature of the water. If we live in California and the ground water temperature is pretty warm at about 65ºF, then the water can get up to 110ºF (45ºF + 65ºF). However if we are in Colorado and the ground water is about 45ºF then the water will only get up to 90ºF (45ºF + 45ºF). If we want the water hotter at this 7.4gpm flow rate then we can look at different units, or the possibility of putting multiple units together.

High Volume Models (6gpm and above @ 45º rise):

Commercial vs. Residential

As always commercial in water heaters means the ability to heat more water, or to heat the water to higher temperatures. The residential models that we sell are plenty for a typical home, and if you have a high use home then we have some new interesting residential solutions for you!

Commercial Capabilities:

Our commercial units are in performance and efficiency the same as our residential units. The biggest difference between a commercial unit and a residential unit is the ability connects several units together. With the commercial units and a manifold you can connect up to 20 units together to achieve a 4,000,000BTU system. The manifold will control the amount of units that are firing to deliver the correct temperature water. The manifold also alternates the firing order so that one unit is not always getting used and others never getting used. It really helps to level out maintenance and to decrease unnecessary wear on one unit. Another feature of the commercial units is there ability to raise temperature to 140ºF for commercial/industrial applications.

Commercial Models:

Residential Capabilities:

Our residential models provide the typical water heater capabilities and capacities for average homes. Some times people use more then some of our largest residential models can supply, so Paloma is coming out with DUOnex™ technology which allows two of their residential units to be linked and provide twice the power of a single unit. This is a simple cable that will plug directly into both units. Unfortunately the DUOnex™ has not been released yet. The residential units in general will allow you to set the temperature of the water. Many water heaters will only allow you to set the out coming water temperature if you have a remote, and only certain models come with remotes. If you would like the remote functionality then watch for the units that use remotes and have them included with the water heaters. The remotes also provide a must have feature for technical issues, they give diagnostic codes which explain what is wrong with the water heater(s).

Residential Models:

(Remotes Included)

(Remotes Not Included)

What cost considerations should I be aware of?

With tankless water heaters it is not about picking out the cheapest model you can. As you have seen throughout this informational guide that you need to pick the model that fits what it is you are doing, or how much hot water you want. There are different brand names that you can choose from, but be sure to consider everything that was mentioned in this reference as it will help you to make the right decision!