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Tankless (On-demand) Water Heater

Talking Points and Considerations

Benefits

Installation Flexibility

• Smaller tanks allow you to utilize more space. Residents appreciate more space for storage and commercially this could be a huge benefit for businesses like restaurants that need a lot of hot water during certain time of the day and also have space restrictions.
• As long as they can be vented they can fit on a wall anywhere
• Models are available that can even be placed on the exterior of a home
• Can make conversions from electric to gas easier if tank needs to be relocated

Ability to Make Hot Water

• Excellent product for homes with soaking tubs, high output shower heads and families with higher demands
• Some of the smaller tankless heaters may have trouble keeping up with demand and are not designed for full home use (Proper unit sizing is important)
• Better temperature control. As demand increases on a standard tank and cold water enters the tank and mixes with the 120° stored water, delivered water temperature will decreases. Tankless heaters have a sophisticated control system that maintains constant temperatures mostly by utilizing a modulating valve.

Cost less to operate that tanked water heaters

• Because they make water instantaneously they don’t have stand-by losses
• They operate more efficiently than conventional tanks. High efficiency storage tanks (S/T’s) generally have an Energy Factor of .6 to .64, tankless heater typically are .75 to .85 or higher
• Tankless do not have a pilot light
• With recent increases in natural gas rates the amount of savings increase as well. One tankless advocate writes, “We are the only country on the planet that uses tanks. I always ask: Do you leave your car running all night for the morning drive to work?”

Have a longer life than tanked heaters

• Typical life of a tankless heater is 20 years instead of 10-15 for typical tank heater

Drawbacks and considerations

Cost

• They are expensive relative to tanked heaters (but because of changes in requirement for conventional tanks & meeting code requirements the gap is closing) Cost of metal, flame barrier tanks & the fact that most storage tanks now require an expansion tank that are typically not required on tankless heaters (see table for addition details)
• Typical Tankless heater lasts ~30% longer that standard tanks

Additional Limitations

• High BTU input rating can mean that interior fuel lines may have to be resized
• For conversions, utility meters may be reaching their capacity on larger homes, this could mean additional cost to replace the meter without adding any load
• Long 5/8” service lines may not be able to handle capacity
• Whole neighborhood with product could experience pressure drops certain times of the year and different times of the day
• Electricity is required
• Re-plumbing on conversions
• See below for more information about meter and service line sizing

Estimated Operating Cost Comparison

Annual Savings, Estimated Equipment Cost, Simple Payback

*The fact that a tankless heaters last 30-50% longer needs to be taken into account.

Installation Checklist (issues to consider)

Verify Adequate Gas Delivery

A tankless water heater has a significantly larger gas input rating meaning that this type of water heater uses a larger amount of gas to heat water only when needed. It is important to make sure the existing meter and service line is large enough to supply the equipment.

Natural Gas Usage-Connected Btu Input - Typical Home

House with Tanked WH		House with Tankless WH
End Use	Btu Input Rating	End Use	Btu Input Rating
Furnace	80,000	Furnace	80,000
Water Heater	35,000	Water Heater	15,000- 175,000
Fireplace or dryer	25,000	Fireplace or dryer	25,000
Range	40,000	Range	40,000
Total	175,000	Total	155,000-315,000

Meter Sizing

- A residential meter can serve appliances and equipment as follows:

Meter size	Delivery Pressure	Total CFH	Total Max BTU/hr. (~1050 Btu’s /CF)
A 250 (typical)	6 “ WC	300	315,000
A 250 (typical)	2 pound	330	346,500
A 425	6 “ WC	540	567,000
A 425	2 pound	600	630,000

 

Natural Gas Service line Sizing (without Excess Flow Valve)

Maximum connected Btu’s per hour on PE Intermittent Pressure service lines:

Service Line Length (ft)	Service size	Maximum CFH	Total Max Btu’s Hr
50	5/8” (typical)	550	577,500
100 (typical length)	5/8” (typical)	400	420,000
150	5/8” (typical)	350	367,500
200 - 300	5/8” (typical)	300	315,000
50	1 1/8”	4,000	4,200,000
100	1 1/8”	3,000	3,150,000
150	1 1/8”	2,500	2,625,000
200 - 300	1 1/8”	1,500	1,575,000

Fuel Line Sizing

Due to the larger Btu input rating of tankless water heaters (varying from ~15,000 to ~200,000 Btu’s depending on demand for hot water) the fuel line serving the appliance must be sized adequately. The installing contractor should check existing piping to be sure fuel line capacity is adequate. For example, a natural gas furnace and standard water heater located together requiring 30 feet of fuel line could use ¾” fuel line and be connected with ½ inch flexible connectors. If a tankless water heater were installed with a furnace the fuel line would need to be increased to 1” fuel line and the connection is recommended to be hard piped to maximize gas flow.

Water Piping Issues

Older homes with galvanized pipe that are restricted with sediment and mineral build-up could result in complaints of low flow of hot water. Although manufacturers say units will work with 15 pounds of pressure from city water the optimum is approximately 60 pounds.

Corrugated flexible water connectors are not recommended because they can reduce the flow of water due to increased resistance. Installing contractor should evaluate low water pressure or low flow of water.

Low Water Flow Appliances and Minimal Usage

Rinsing dishes with a small flow of hot water and some ENERGYSTAR appliances with very low hot water demands and can pose a possible problem for tankless applications. Most tankless water heaters need a minimum of .5-.7 gallons of water flow to activate the system. A demand of less than this could result in no hot water to the appliance or sink.

Maintenance and Servicing

Tankless water heaters have a water inlet filter screen that can accumulate sediment and reduce water flow. The screens should be cleaned after initial installation and then regularly cleaned. Generally speaking tankless water heaters have less ongoing servicing needs than conventional tanks if the screens are regularly checked/cleaned.

• Limited servicing is available because of limited product knowledge (check with installing contractor to be sure servicing is readily available)

Investigate Warranty

Tankless water heater warranties are generally longer than those of tank-type units. Typical limited warranties (parts only) are 2-5 years for the unit, and 7-10 years for the heat exchanger. Expected life of tankless water heaters is 20 years.

Standard tank-type water heaters have usually have limited warranties of 1 year, tank warranties of 5-10 years and the expected life is between 10 and 15 years (PATH, Partnership for Advancing Technology in Housing).

Use Hot Water Wisely

The tankless water heater can easily meet the demand for unusually large quantities of hot water for soaking tubs, multiple head showers and other uses in some of today’s homes more efficiently than tanked systems. We encourage good stewardship in both water and energy use and that hot water use be watched closely. The ability to heat water continuously could result in longer showers and therefore result in higher bills if you are not careful.

 

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