Possible solutions for low inlet temp and high flow rate?

Users who are viewing this thread

phurley12

New Member
Messages
2
Reaction score
0
Points
1
Location
Oregon
This seems to be a very common problem as it is not always readily explained or understood that tankless water heaters cannot always contend with the combination of low inlet temp and high flow. Thus, I fell victim to the appeal of the tankless on-demand water heater.

I recently bought a house and did a remodel, replacing the non-functional leaking tank heater that was over 25 years old with an Eco27 by ecosmart. It has worked well until I installed a higher flow rainfall showerhead in the shower that pulls about 4.4 gpm. Living in Oregon with inlet temp from our well being about 55F the best that it can manage is 85-90F which is just under a fairly comfortable shower. All this while not being able to run any other hot water taps or appliances.

After scouring the internet and reading post after post on many different forums I think I have a couple different options and want to know what would be the best to move forward with.

In no particular order:

-Energized low-temp setpoint tank style water heater piped in series before the tankless. In theory providing already semi heated water to the tankless heater making a larger temp rise easier. Downsides being extra energy use for maintaining temp and not knowing if the Eco27 has a max inlet temperature (awaiting email from ecosmart)

-A smaller tankless water heater in series just before the larger one. I have the space on my electrical service which is 200A but would adding another small one just before really make that much of a difference or just be a waste of money and energy? I also realize it will double the min flow rate for activation which is 0.3gpm for most ecosmart models making it harder to activate with low-flow fixtures.

-A tempering tank placed somewhere that would allow incoming water being used for hot water to increase in temp via heat exchange with the surrounding interior. downsides being I don't have room underneath my house for a large tank which means i'd have to put it into the pantry next to the tankless one. Plus our house stays relatively cold most of the time since we use minimal heating.

-solar pre-heaters mounted on the roof. I couldn't find much info on this. We definitely have a south facing roof that I could mount something like this on but again, running up against the issue of not knowing if ecosmart has a max inlet temp.

I would love input on any of these options as well as others I may not have considered. I have ample ability to do different plumbing configurations and wiring configurations as I have a friends who are professionals and will help for free/beer.

Specs/details
Eco27 27kw tankless water heater
inlet temp: 55F
max flow desired at 105F: 4.5gpm
electrical service: 200A
 

HardDrinkin'Lincoln

New Member
Messages
3
Reaction score
0
Points
1
Location
Central Wahington
Let's run the numbers. To heat 4.5gpm at 55F to 105F requires 1,874 btu/min. or 33 kW. So right at the start we can see you are short 6 kW of power power. If you put a 6 kW preheater before the Eco27 you can raise the incoming water temperature by 9F to 64F. The Eco27 would then be able to provide the desired 105F at 4.5gpm.

The alternative to directly preheating the water with 6 kW is a small electric tank type water heater with a heating element of 1 or 2 kW. That would provide a buffer of 15 to 30 minutes depending on the tank volume, and the duration of the 4.5 gpm flow.
 

Bannerman

Well-Known Member
Messages
4,339
Reaction score
616
Points
113
Location
Ontario, Canada
Most Natural Gas or propane fueled tankless units are capable of heating water more rapidly which will support greater temperature rise and higher flow rates.

Consider Navien NPE-240 series models have a maximum heating input of 199,900 BTUs which can support up to 7.8 GPM @ 50℉ temp rise. Navien's smaller NPE-180 series max fire rate is 150,000 BTU, will support 5.9 GPM @ 50℉ rise.

https://www.navieninc.com/series/npe-a

To obtain adequate performance from your existing electric tankless unit, without prewarming the water or installing a second identical unit plumbed in parallel, the flow rate would need to be reduced which probably will eliminate use of the 4.5 GPM rainfall shower head to return to a 2.5 GPM standard head.
 
Last edited:

phurley12

New Member
Messages
2
Reaction score
0
Points
1
Location
Oregon
Most Natural Gas or propane fueled tankless units are capable of heating water more rapidly which will support greater temperature rise and higher flow rates.

Consider Navien NPE-240 series models have a maximum heating input of 199,900 BTUs which can support up to 7.8 GPM @ 50℉ temp rise. Navien's smaller NPE-180 series max fire rate is 150,000 BTU, will support 5.9 GPM @ 50℉ rise.

https://www.navieninc.com/series/npe-a

To obtain adequate performance from your existing electric tankless unit, without prewarming the water or installing a second identical unit plumbed in parallel, the flow rate would need to be reduced which probably will eliminate use of the 4.5 GPM rainfall shower head to return to a 2.5 GPM standard head.


unfortunately i do not have access to natural gas and do not want to install a propane tank on the property. Nor do i have enough electrical power available to install another identical 27kw heater.

I will probably look at installing a smaller eco heater ahead of the eco27 in series as I don't have any fixtures that run at less than 1gpm.

Thanks for the input.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks