It is important to understand the relationship of ground water temperature and the flow rates of tankless water heaters. In Southern US States a tankless can produce substantially more hot water as the incoming water can be as warm as 75 degrees. The tankless system doesn’t have to work very hard to get the water up to 120 degrees (45 degree rise). Here in Ontario it’s a different story, our winter water temperatures dip into the low 40 degree range, this puts additional pressure on the tankless and requires the system to produce more heat to achieve the large temperature increase (roughly a 78 degree increase).
Here in Toronto we recommend tankless systems that are on the larger end of the spectrum, these systems usually produce about 199,000 BTU. This much energy allows the production of an adequate amount of water for most residential home demands from Toronto’s low winter water temperatures.
The Picture below shows water temperatures for most of the USA and some of Ontario of which you can determine average winter water temperatures for many cities and locations.
Although most tankless systems utilize very similar systems to heat water efficiently each tankless manufacturer has their own proprietary systems for heating the water. The unique of each system has created minute differences in hot water production at certain temperature levels. Though a lot of digging we have created a chart containing the most popular tankless systems and their respective hot water output at certain intervals.
We chose a 77 degree rise as a baseline for winter water temperatures that a tankless owner in Toronto or surrounding area would experience. We also included the stats for a 35 degree rise which is more common for summer water temperatures in Ontario. These two levels also enable you to see the production difference incoming water makes on a tankless water heater.
| Tankless Brand & Model | 77˚F Rise | 35˚F Rise |
|---|---|---|
| Bosch Tankless Systems | (Gallons Per Minute) | (Gallons Per Minute) | Bosch GWH 715 | 4.2 | 9.2 |
| Bosch GWh C 920 ES | 5.4 | 11.8 | Bosch GWH-800ES | 4.6 | 10.1 |
| Bosch Therm C-1210 | 5.4 | 12.1 | Bosch Therm C-1050 | 4.7 | 10.5 | Bosch Therm C-950 | 4.2 | 9.3 | Bosch Therm 940 | 4.2 | 9.3 |
| Navien Tankless Systems | (Gallons Per Minute) | (Gallons Per Minute) | Navien 180 | 3.8 | 8.3 | Navien 210 | 4.6 | 10 | Navien 240 | 5.1 | 11 | Navien 180A | 3.8 | 8.3 | Navien 210A | 4.6 | 10 | Navien 240A | 5.1 | 11 |
| Rinnai Tankless Systems | (Gallons Per Minute) | (Gallons Per Minute) | Rinnai RL94i | 4.1 | 9.1 | Rinnai RL75i | 3.9 | 7.5 | Rinnai RC98i | 4.9 | 9.8 | Rinnai RC80i | 3.9 | 8 |
October 15, 2018
Not a problem. 4.2 gallons per minute would be for a natural gas or propane powered tankless, an electric tankless would produce far less hot water. A tankless can provide infinite hot water, so in this case it could make 4.2 gallons of hot water continuously, it wont stop until you turn the tap or shower off.
September 26, 2018
Hi there so if the manufacturer says 4.2 GPM in winter time for example, what does that mean? For how many minutes can it provide that type of output? Sorry but trying to understand the numbers. I’m newbie to tankless but looking for electrical on for my house in Toronto
January 16, 2018
Thanks, you were correct, everything fixed now.
April 16, 2016
A simple way to increase your GPM flow, is to use the hot waste water from showers and sinks that goes down the drain. A drain water heat recovery system will raise the temperature of incoming water (40degrees) up to between 75-85 degrees before it supplies your tankless OR hot water tank. Use less energy to heat water, reduce costs and DON’T run out of hot water ever again. Simple to install.
November 11, 2015
We have one that came with the house so it’s at least 5 years old and probably much older. It only heats the first sehowr and then the rest of the people get a mediocre to cold sehowr. So, now I have a tank and the tankless, hot water in the sink that will burn your hand and a comfy sehowr. I am sure though that they have improved over time or the previous owners bought a cheapy one. Keep us posted. I’d love to hear how it works for you.