Frequently Asked Questions about Tankless Water Heaters
What is a tankless water heater?
Tankless water heaters are typically gas fired units that create domestic hot water on demand. They are compact and can produce and supply endless streams of hot water to multiple outlets at once without any fluctuation in temperature. They have been commonly used in the metro Austin, TX area since for about the last twenty years. Major tankless brands include Rinnai® and Navien.
What type of fuel to Rinnai® and Navien tankless water heaters use?
Both Rinnai® and Navien use either natural or LP gas for fuel.
Are there tankless water heaters that do not require natural or LP gas?
Electric tankless models are also available (from other brands) but they are typically used as smaller point of use heaters for a remote lav or laundry sink rather than as a whole house system. This is because they have two distinct flaws:
- First, the cost of electricity is, on average, significantly higher than natural gas. The operating cost of electric tankless units tend to be much higher than gas fired units.
- Second, electric tankless water heaters can only produce a relatively small amount of hot water. This is because they require a large amount of electrical current to produce a significant amount of hot water. For example, in order to have the same capacity as our smallest gas fired unit you would need to provide about 120 amps of power at 230 VAC to an electric tankless unit. This represents well over half the amperage capacity of a typical home and 5 times the amperage of a typical central air conditioning system.
Are there different types of gas fired tankless water heaters?
Yes, there are four basic types of Gas fired units:
- The earliest modern tankless units were about 80% efficient. Rinnai® is a leader in tankless technology and was the first major manufacturer to create a substantial North American market starting in about the year 2000.
- Condensing tankless water heaters are between 90 and 96% efficient, and have UEF (Uniform Energy Factor)of up to 0.97. Both Rinnai® and Navien off a number of condensing tankless models.
- Condensing tankless models with integrated recirculation systems are available for both Rinnai® and Navien. The Rinnai® RUR and the Navien NPE-A2 series both have onboard recirculating capabilities which can ensure instant access to hot water throughout you home.
- Combi Units are a hydronic boiler that has the ability to generate hot water on demand like a dedicated tankless unit. Navien is a leader in combi technology and offer very high efficiency for both space heating and domestic hot water.
How is a tankless system different from traditional water heaters?
Conventional water tanks heat and store hot water around the clock. Because of this you are heating and re-heating water, and constantly losing energy up your vent and through the walls of the tank. A tankless water heater only comes on when you start to use hot water, and immediately shuts off when you are done, so you are not wasting energy when you do not need hot water.
Tankless water heaters have much more effective heat exchanger and burner systems than conventional tanks. This allows you to utilize a much higher percentage of your energy dollar rather than wasting it up the vent stack of a conventional tank water heater.
What is the efficiency rating of Rinnai® and Navien tankless water heaters?
Water heater efficiencies are now based on their UEF rating. This is the Uniform Energy Factor. The higher the UEF rating, the more efficient the system. UEF represents the ratio of fuel consumed verses the portion of fuel which is effectively utilized to heat hot water. For example, id a system has a UEF of 0.80, 80% of the energy is utilized for water heating, and 20% is lost through venting and other losses. Current gas and electric water heaters have UEF rating from about 0.56 to 0.96.
Does a higher UEF rating mean that you will always experience lower hot water heating costs?
That depends. For a given volume of hot water a higher UEF rating in a properly maintained water heater will always have a lower operating cost than one with a lower UEF.
However some homeowners do not experience as much savings with tankless because there is no longer an artificial barrier to hot water use. With conventional tanks you will run out of hot water after a period of use, but with a tankless model this will not happen. In some homes this increases the gallons of hot water used, but it’s great to have all the hot water you need, when you need it.
Are tankless water heaters more expensive to install?
Yes, they can typically cost as much as two to three times that of the cheapest tank style water heater. However, they typically have a longer life, save energy dollars, provide unlimited hot water, and are eligible for rebates and incentives that can partially offset this higher cost.
How long does a tankless water heater last?
The life expectancy of a modern tankless water heater is up to 20 years. Actual life is a function of water quality, proper maintenance and usage rate. This is almost twice as long as a tank water heater making them a great value over the life of the unit.
Do tankless water heaters have any drawbacks?
- Their purchase cost it typically more than a tank style installation but this is somewhat offset by incentives and rebates in most places.
- Residential tankless water heaters fire at up to 199,900 Btu/Hr so you will want to ensure that your gas supply can handle this peak load.
- Tankless water heaters do not have any stored hot water, so if you have a period of time where you need a very high flow rate of domestic hot water a tankless model may have trouble meeting that momentary demand.
- Tankless water heaters are technically advanced, so you will want to make sure you have someone that is properly trained and has the correct tools to install and service your water heater.
Are there utility or tax incentives that will offset the cost of a new Navien or Rinnai® tankless model?
Yes, the us a Federal tax credit of $300, and a local rebate of $250 for natural gas customers of Atmos Energy for the installation of condensing tankless models.
Are water heaters EnergyStar rated?
Yes. Both Rinnai® and Navien offer a number of EnergyStar certified models.
Are gas fired tankless water heaters worth the money?
Tankless water heaters are a get value, but they are not for everyone. How many people are in your household? How long are you planning and staying in your current home? Do you have access to natural gas? Are you short on mechanical space? In general, the larger your family and the greater your hot water demand, the more attractive a tankless unit will be. A talk with one of our plumbing exerts will make it easier for to decide if tankless is right for you.
Are exterior tankless water heaters a safe choice in the Austin, TX area?
There are both interior units (which are sealed combustion and vented outdoors) and exterior units. All Rinnai® and Navien units are designed to operate properly to outdoor temperatures well below 0° F. Exterior units will not freeze even on the coldest night of the year as long as they have electrical power and gas. However, the water connections to an exterior unit must be properly protected from cold conditions by the installer to prevent these water lines from freezing.
Do gas fired tankless units require power to operate? Do they use a lot of power?
Gas fired tankless water heaters do require 120 VAC power to operate. The electrical consumption is quite small. This varies based on the size and type of the unit, but this is typically less that 100 watts per hour during operation, and adds up to only a few dollars of electrical energy per year.
Do modern tankless units utilize a pilot light for ignition?
No. Both Navien and Rinnai® units utilize a high efficiency direct spark ignition system. This is both more efficient and more reliable.
How interior tankless units vented?
There are two types of venting based on the efficiency of the tankless unit. Non-condensing o.80 UEF units are all sealed combustion and utilize a power draft system. The vent system draws combustion air in from outdoors and expels flue gas back out through a stainless steel side wall or roof penetration.
Condensing models with 0.90+ UEF ratings are also sealed combustion, but because their fuel gas temperatures are much lower than the non-condensing models they can use PVC pipe for both intake air and flue gases.
Why do all interior Navien and Rinnai® units require exterior combustion air?
Tankless water heaters have a large gas capacity and can need a lot of combustion air. Most homes do not have the free space necessary to install a tankless water heater to code with out making significant modifications to your home. For us, it just makes sense to do it right the first time and not take the risk associated with improper interior make-up air design.
Even if you do have the huge open space necessary to install a system with interior combustion air, that unit will be drawing thousands of cubic feet of conditioned air from inside your home each day, and will discharge it outdoors. To replace this, outdoor air will be drawn back into your home through infiltration and will need to be warmed or cooled by your HVAC system. To us, this is an unacceptable waste of energy.
Do I get instant hot water at my point of use with a tankless water heater?
Without a recirculation system, it’s typical to have a slight 1 – 2 second temperature drop as the begins its operating cycle. The wait time to get hot water at a point of use is dependent on the distance between your tankless water heater and the location of any hot water faucet within your home.
Both Navien and Rinnai® offer recirculating models that can deliver almost instant hot water a your point of use.
What is the minimum flow rate to activate a tankless water heater?
Rinnai® and Navien tankless water heater must be able to sense water flow in order to initiate operation. Most Rinnai models will operate with flow rates as low as 0.5 gallons per minute. This is the lowest minimum flow rate in the industry and is an important benefit.
What is meant by a tankless variable firing rate, and what does it mean to me?
Unlike old style tank water heaters which fire at only one rate, all Navien and Rinnai® tankless water heaters will use only the amount of gas necessary to heat the hot water being used at any given time. To do this they measure the incoming water temperature and the flow rate, compare that to the desired output temperature, and fire at the rate necessary to meet this need. If you change any of these variables, the tankless unit re-calculates and adjusts its firing rate accordingly. The tankless unit will therefore fire anywhere between its minimum and maximum firing rate.
Can I interact with my tankless heater?
Yes, all Rinnai® and Navien units come with a multi-function touchpad. Homeowners can use this interface to set outlet water temperatures, turn the system on or off, and view and service or warning indicators. Properly trained service personnel can also use this interface to fine-tune installation parameters, view past service history, and troubleshoot your unit if you are experiencing problems.
Can I use my Apple or Android mobile device to interact with my tankless water heater?
Rinnai® and Navien have convenient Apps that allow homeowners in interact with their unit no-mater where they are.