Today’s tankless water heaters

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One advantage of tankless is that the small size offers flexibility in where to locate the unit.

By Simon Blake

Tankless water heaters have been in the North American market for some time now and the market continues to grow rapidly as homeowners and contractors alike have become more comfortable with the technology. Like any appliance, sizing is critical, but there are now models that cover virtually every natural gas or propane application.

Today the trend is towards highly efficient condensing models and smart home connectivity. As well, more and more home owners are looking for DHW that really is instantaneous, leading to an increasing demand for DHW recirculation, remarked Chia Lin, water heater product manager for Navien, Irvine, Calif.

For manufacturers, the biggest struggles are to make consumers aware of the technology and to minimize the installation cost to make tankless more competitive with other water heating solutions.

Common venting is being used in some jurisdictions for multiple units.

“The challenge is getting the contractor to do the installation for a comparable margin as they do for a tank,” said Jason Fleming, vice president of sales and marketing for Noritz, Fountain Valley, Calif.

“Combo applications (a tankless unit paired with an air handler) are becoming more popular with new home construction companies,” said Mark Williamson, national sales manager – boilers, for Bradford White Canada, Halton Hills, Ont.

The tankless advantage

Tankless DHW heaters offer several advantages. The first thing that manufacturers tout is “endless hot water.” But there’s a proviso with that; the unit must be sized to handle the load. As manufacturers have introduced larger units, this has become easier to achieve.

Energy efficiency is another plus. “When you go out of town for two weeks, that unit stays off for two weeks; it only uses energy when you use it,” said David Federico, brand director for Rinnai, Peachtree City, Georgia.

The already high efficiencies are increasing as tankless units adopt condensing technology. Traditional units have an energy factor (EF) of about 0.82 while condensing models operate in the range of 0.96, noted Lin.

The carry-on suitcase size of the typical tankless unit saves space as builders look to maximize living areas. Serviceability is another advantage. The lifespan is typically about 20 years and tankless units are designed to be repaired. Noritz recently introduced a 25-year warranty.

Home automation

Today’s homeowners are looking for automation. “Overall we see an increasing trend in connectivity with the development of apps capable of communicating and interacting with tankless water heaters,” remarked Afonso Cunha, product engineer for Bosch Thermotechnology, Londonderry, New Hampshire. “These apps are targeting both the end-user and the contractor with information and features that are relevant to these groups.”

Today’s mechanical room; this unit is located in a bathroom closet.

“With the popularity of smart home devices, you now have the ability with Navien’s NaviLink to control temperatures remotely, access usage data, receive diagnostic notifications and enable custom recirculation schedules resulting in additional energy savings,” noted Lin.

Rinnai Sensai condensing models with recirculation are equipped with Wi-Fi that operates though an app, Google Smart Home, Amazon Alexa, etc. “You can say Alexa, I need hot water, and it will kick on the pump,” said Federico.

Right sizing the appliance

Sizing is where contractors can run into trouble. There are two critical factors; peak water usage and the winter groundwater temperature in the region.

It really pays to talk to the customer and understand their needs. “Usage patterns in a typical family are dictated by shower usage,” noted Fleming. “With a tankless water heater, continuous usage is no problem, the main consideration is simultaneous usage. This is inverted from a traditional tank type where continuous periods of usage is the major limiting factor.” If the unit is slightly undersized, the user will still get hot water but at a reduced flow.

Top mounted water connections, long PVC vent runs make retrofits easier.

It’s also worth asking about future renovations. If the customer plans to add a “carwash” multi-nozzle shower system, the contractor needs to size the tankless unit accordingly.

The other important factor is the temperature difference – Delta T – between the groundwater and the desired DHW temperature. “The higher the difference, the higher the energy needed to heat the water. This is why in colder climates, with a lower ground water temperature, it is usually recommended to go for a higher capacity for a given flow rate,” said Cunha.

“I would not install single tankless units in colder climate applications that require more than five gpm for an 85F rise from a 35F water supply,” added Williamson.

Ease of installation

A key focus for manufacturers has been to mitigate the increased labour costs by making installation as easy as possible.

“Top mount water connections save a bundle of time in going from tank to tankless,” noted Fleming. Venting usually needs to be changed and manufacturers offer many options, including two and three-inch PVC. Bradford White’s Infiniti K-Series tankless unit, for example, can be vented up to 280 ft. with two or three-inch PVC or polypropylene.

Gas line sizing is also a major consideration. The typical gas line into a home is half inch and most tankless units today are designed to work with that.  However, sometimes the line must be upsized to ¾-inch and, in some cases, the meter too. “You will want to size the gas line for maximum Btu/h input specifications for the individual tankless unit,” noted Lin.

Garage installations are common in the U.S., not so much in Canada.

“Follow the B149.1-15 gas code and do not take shortcuts,” advises Williamson. “You are replacing a 40,000 Btu/h (storage tank) with an appliance up to 199,000 Btu/h; they require different gas lines. An undersized gas meter will actually spin faster and charge you for more than you actually use.”

The contractor also needs to keep in mind the gas requirements of other appliances in the home – a stove, fireplace or dryer, for example.

New gas valve technology

New gas valve technology may reduce the need to upsize gas lines and/or meters. In it’s condensing Sensai model, for example, Rinnai uses a zero-governor gas valve, which basically sucks the gas into the unit rather than relying on gas pressure to push it in. This largely solves the problem of variable gas pressure.

“Basically, it adapts to any fluctuations in gas pressure without the unit cutting out. The consumer benefit is that in a lot of applications you are able to use your existing (half-inch) gas line and not have to upsize the gas line, which is a major expense,” said Federico.

All manufacturers offer training, and it’s critical to be trained on the actual products that you are installing. “You need to make sure you have the product knowledge so that you are not quoting someone for work that doesn’t necessarily need to be done because that will result in a lot of times losing that sale.”

Customer expectations

It is important that the contractor spend some time educating the customer, especially those that are new to tankless. “The most relevant topic is how fast hot water will reach the taps,” remarked Cunha. “The term ‘instantaneous’ is commonly used to describe a tankless water heater… The problem is that this term is sometimes misunderstood and some homeowners expect hot water to reach the taps instantaneously.”

This is a more typical basement installation.

Tankless units must also be flushed about once a year, depending on water quality. It’s something the homeowner can do, or the contractor can do as part of a maintenance program, which also includes changing the filters. Some of today’s Wi-Fi enabled tankless units allow the homeowner to assign a plumber who receives an error code if anything goes wrong.

Recirculation systems

Many tankless units are installed with recirculating DHW systems. Some feature an integrated recirculation pump and others have controls for an external pump.

The Navien NPE-A model, for example, has a built-in recirculation system including the pump and a buffer tank to prevent the dreaded “cold water sandwich” in which the users gets a short burst of warm water, followed by cold and then warm again.

There are two basic ways to do recirculation; the first uses a dedicated recirculation line, the second is to install a crossover valve at the furthest fixture from the unit.

Many new homes are being specified with a dedicated return line. In a retrofit, adding a crossover valve between the hot and cold-water lines is easier. When the water cools, the valve opens and uses the cold-water line as a return.

Unlike storage tanks, tankless heaters have a minimum activation flow rate that is typically 0.5 gpm. “The recirculation pump needs to be able to push at least this minimum amount of water through the return line in order to function,” noted Fleming.

It is important that the homeowner knows how to set the recirculation control so that the system operates only when hot water is needed. “You don’t want to have it set so it recirculates every 15 minutes; that sort of defeats the benefit of having tankless,” said Federico.

Moving forward, contractors can expect to see larger capacity units, further smart home integration, building management system integration and other features, noted Lin.

It is likely at some point that all tankless DHW heaters will be required to be condensing.

“As customers and municipalities are looking to reduce the carbon footprint, moving towards the higher efficiency products is a direction we expect to continue,” said Fleming.

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