InspectAPedia®   -   Search InspectApedia

Tankless water heater (C) Carson Dunlop AssociatesHot Water Heating Capacity of Tankless Water Heaters
Demand Water Heaters or Instantaneous Water Heaters or
Endless Hot Water Systems

Hot Water Heating Capacity of Tankless Water Heaters: this article explains the hot water heating capacity of tankless water heaters, also called instant water heaters or "on demand" water heaters.

The quantity hot water is delivered can be expressed in gallons per minute of hot water at a particular temperature rise over the incoming water temperature.

We also discuss the question of what "endless hot water" really means.Our page top photo illustrates three Bosch instant water heaters for sale in a Home Depot in Celaya, Mexico in 2012.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Typical Tankless Water Heater Capacities

Rheem tankless water heater © D Friedman at InspectApedia.com A typical small point of use electric tankless water heater may be able to increase incoming water temperature by about

A larger electric tankless water heater may be able to increase incoming water temperature by about

Some tankless water heaters are rated at 9.8 GPM but be sure to check the temperature rise that the heater can provide at that flow rate (35 deg.F.).

We haven't seen a tankless water heater providing more than 5 gpm flow rate at high temperature rise (over 65 degF) rating.

If your building needs higher hot water flow rates you may need to use a conventional hot water tank or a gang of tankless water heaters.

If you're trying to provide 100° water, a 35 deg.F. temperature rise assumes an inlet water temperature of 65°F - not something you can count on in cold climates.

In our OPINION, even 100° temperature rise may not be high enough if the system is being used with a mixing valve or on long piping runs that we described earlier.

Does a Tankless Water Heater Provide Endless Hot Water?

Tankless water heater (C) Carson Dunlop AssociatesWell yes, no, and sort-of.

Limitations on Hot Water Production Rate of Tankless Water Heaters

Each model of tankless water heater is rated to provide a specific water temperature rise, for a given water flow rate.

[Sketch of a point of use tankless water heater courtesy of Carson Dunlop Associates]

Typically a tankless water heater can provide 2 – 5 gallons (7.6 – 15.2 liters) of hot water per minute.

For example, a heater may be capable of increasing the temperature of incoming water 60 deg. F. at 3 gallons per minute flow rate.

The temperature rise that a tankless water heater can provide and the water flow rate that it can support depend on the heater's BTU output capacity which in turn is a function of the fuel used (gas-fired or electric) and the efficiency and the size of the heater.

Also see tankless water heater Problems & Defects where we describe the Tankless Water Heater Cold Water Sandwich Effect. Readers should also

see ALTERNATIVE HOT WATER SOURCES to distinguish among these types of hot water producing systems.

The original text of this article was provided courtesy of Carson Dunlop Associates - that text has been edited and may not entirely reflect CD's views.

Our OPINION is that readers looking for plenty of hot water heated efficiently should also consider the heater we describe

at INDIRECT FIRED WATER HEATERS

 




ADVERTISEMENT





Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Comment: decide against the tankless system

(June 30, 2011) Don Wells said:
Your findings helped me to decide against the tankless system as it seems to be high maintenance. I'll stay with the gas water heater with a good insulation rating.

Reply:

My opinion is that the life and performance as well as maintenance of tankless water heaters can be good depending on the local water chemistry. Hard water can be a problem for some units.


...

Continue reading  at TANKLESS WATER HEATER CONVERT TO? or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

Suggested citation for this web page

TANKLESS WATER HEATER CAPACITIES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to WATER HEATERS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification
when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Comment Form is loading comments...

Citations & References

In addition to any citations in the article above, a full list is available on request.



ADVERTISEMENT