Two tankless water heaters?

bigskypc50 · 09-18-2018, 09:50 PM

Greetings everyone I have very cold ground water and very low pressure where I live. I have not had good luck with tankless water heaters in the past, so I am wondering if I bought two of the Excel tankless ventless water heaters and fed the output of the first unit into the second one if I could get good nice hot water out of that at the max 1.6GPM flow they are rated for?

Tango · 09-18-2018, 09:55 PM

You might check with "Ol' Trunt" (aka; Jack). As I recall, he discovered that you can over pressure the system if you are not careful and blow stuff up with too much heat/steam pressure. But...(also as I "recall") I think he figured out a fix.

milkmania · 09-18-2018, 10:07 PM

Quote:

Originally Posted by bigskypc50

Greetings everyone I have very cold ground water and very low pressure where I live. I have not had good luck with tankless water heaters in the past, so I am wondering if I bought two of the Excel tankless ventless water heaters and fed the output of the first unit into the second one if I could get good nice hot water out of that at the max 1.6GPM flow they are rated for?

personally, I've got great pressure... But, being the inquisitive one, I've experimented with my eccotemp L5.

I've got a portable hottub, and had a harbor freight transfer pump 12volt laying around... I plumbed to pick up water from the tub, feed through the heater, and back out to the tub... worked awesome! now, I did not run it back through a shower head to see if I'd like the pressure... but, what I saw on the outlet hose was similar to my regular water supply pressure.

Bryan at Eccotemp showed me how to adjust the propane burner and water pressure inlet to a range outside of factory specs, with 2 adjustment screws... so, that along with a standard garden hose ball valve... I can hit 192 degree outlet temps!

I know it doesn't answer your original question... but it might give you an idea what your heater is capable of.
personally, I think hitting the second heater with hot water isn't going to help you much. there might even be a high limit switch incorporated in your heater.

HF pump $39.99... wait for a sale!
https://www.harborfreight.com/12-vol...ump-63324.html

garden hose ball valve
https://www.amazon.com/Gilmour-Conne.../dp/B0006U66B6

also created a PEX manifold with Shark Bite ball valves and fittings to go to the shower and clothes washer... has worked great for over 2 years
Shark Bite fittings are awesome, because they're reusable!

ol trunt · 09-19-2018, 12:01 AM

Forget the second water heater. Remember, the Ecotemp heats ambient temp water by a set amount (can't remember the specifics). Therefore the hotter the water going in the hotter the water coming out. I put a recirculating circuit on my ecotemp to assure me of hot water nearly instantly. The problem was that as input ambient rose in temp so did output--until my hot water lines grew soft and finally gave up!?! I solved my problem by installing a thermocouple on the outlet that shut down the ecotemp at the temp I wanted. That works great. You migh consider a dedicated hot water tank coupled with a thermostat and a recirculating valve. I use a dedicated water pump one for hot and one for cold. This arrangement provides me with flawlessly regulated hot water temps and has done so for a couple of years.
Jack

ThunderstruckStudios · 09-19-2018, 12:46 AM

Bigsky,

Be careful of overheating the water. Even if the bulk of it doesn't boil (reach 212 F), there's a phenomenon called critical heat flux - basically a really thin layer of water next to the hot outer wall of the pipe (that's being heated by propane) can boil locally, creating a vapor gap, which then insulates the water in the center of the pipe. The temperatures inside the pipe can jump up super rapidly, ultimately causing the pipe to fail from excessive temperature of excessive steam pressure.

Short version: rapid overheating = pipe bomb. Not recommended.

Njsurf73 · 09-20-2018, 10:24 AM

What about a small (20 gallon) holding tank with a water pump. Would solve the low pressure issue and should allow the water to at least come up to ambient temperature and you don't have the worry of overpressure.

Quote:

Originally Posted by bigskypc50

Greetings everyone I have very cold ground water and very low pressure where I live. I have not had good luck with tankless water heaters in the past, so I am wondering if I bought two of the Excel tankless ventless water heaters and fed the output of the first unit into the second one if I could get good nice hot water out of that at the max 1.6GPM flow they are rated for?

Rivetboy · 09-20-2018, 12:44 PM

Quote:

Originally Posted by ol trunt

Forget the second water heater. Remember, the Ecotemp heats ambient temp water by a set amount (can't remember the specifics). Therefore the hotter the water going in the hotter the water coming out. I put a recirculating circuit on my ecotemp to assure me of hot water nearly instantly. The problem was that as input ambient rose in temp so did output--until my hot water lines grew soft and finally gave up!?! I solved my problem by installing a thermocouple on the outlet that shut down the ecotemp at the temp I wanted. That works great. You migh consider a dedicated hot water tank coupled with a thermostat and a recirculating valve. I use a dedicated water pump one for hot and one for cold. This arrangement provides me with flawlessly regulated hot water temps and has done so for a couple of years.
Jack

Good Morning Jack,

So my undestanding is you have an auxillary water tank with a pump connected to the output side of the water heater . The water heater and the pump to recirculate hot water through the tank are on a thermostat.
Do I need more coffee?
Is the recirculating valve supposed to read "pump"

Joe

bigskypc50 · 09-24-2018, 12:42 PM

Wrote the manufacturer. They said it should not be a problem with that setup.

Hello Eric,

Yes you can connect them in series to achieve a higher delta in temp increase for 1.6gpm.

You can tinker with the gas knob and the water flow knob for the desired performance

You can buy them at this link:

http://excelonlinestore.com/excel-16...p-ventfree-lpg

Excelamerica , LLC
Fernan Ech Usher
6010 NW 99 Ave
Unit 107
Doral, FL 33178
USA

gasflex is a registered trademark USPTO

ol trunt · 09-24-2018, 03:28 PM

More coffee----

2 pumps, 1 hot, 1 cold both from same tank.

water heater output goes to both the faucets and to a solenoid valve which diverts hot water back to main tank. Water can flow through either or both. As long as there is water flow and pressure, the heater will stay lit rather than constantly cycling. This assures hot water "instantly".

These heaters maintain a temp differential based on the ambient temp of the inlet water. As the main tank drew down, its ambient temp went up due to the recirculation of hot water --all the way up to 150 degrees F. That was hot enough to melt the joints on my PVC water pipes and make a mess. With a thermocouple switch on the heater output side I am able to control the upper temp limit within a couple of degrees without nearly as much heater cycling.

If you are stuck with very cold inlet water, a 2 tank system (1 hot, 1 cold) would hasten getting your inert water temp to within the desired heater temp differential. Ha! Clear as mud.
Jack

dan-fox · 09-24-2018, 09:22 PM

Quote:

Originally Posted by ol trunt

These heaters maintain a temp differential based on the ambient temp of the inlet water. As the main tank drew down, its ambient temp went up due to the recirculation of hot water --all the way up to 150 degrees F. That was hot enough to melt the joints on my PVC water pipes and make a mess. With a thermocouple switch on the heater output side I am able to control the upper temp limit within a couple of degrees without nearly as much heater cycling.Jack

Do I misunderstand your setup, or are you at risk of having 100 degree water coming out of the cold faucet? Not conducive to a good shower if both faucets are the hot faucet.

ol trunt · 09-24-2018, 10:35 PM

No more coffee for you. Ha, Ha. Jack

Hotpuppy · 09-29-2018, 05:26 PM

Some brands divide the flow and allow each heater to heat to the setpoint. The heaters restrict flow to meet the output target.

It may make more sense to look at where you tank is and what your use case is. If you are boon docking in the Arctic then you may need supplemental fuel heat.

I'm planning to install a water heater that can run LPG, Electric, and take a feed from the engine coolant to scavenge heat.

In addition to this I'm going to add a tankless heater for when I'm plugged in and not paying for power.

Lastly, a tempering valve on the output side will make your water go a long way. I have a tankless at my house and it was set to 120 max at the factory. I originally was going to crank that up but I've since found it's liveable. On a tank water heater I might set that higher and use a tempering valve to meet the setpoint while consuming less of my heated water.

o1marc · 10-01-2018, 12:12 PM

Does the efficiency change on size of heater. Does the lower GPM heat faster than 4.5GPM unit? I checked at my home and it takes 50 seconds to fill a gallon jug. Do I need/want the larger capacity, or is it overkill? BTW, the hot water hadn't reached the faucet in a minute, such a waste of water.

Hotpuppy · 10-01-2018, 12:42 PM

Efficiency is largely a factor of design.

What I found is that the ultra-efficient heaters were really expensive and produced a corrosive condensate that shortened the heater life and created new issues. When I did the ROI against natural gas prices at my house.... well there wasn't one. So I bought the less efficient, lower maintenance heater.

I think realistically the same thing applies for RV's.

My use scenario divides into "with utilities and without."

With Utilities means at a campground with water, 30A+ electric, and sewer connections. At that point I'll use a small electric tankless so I can enjoy a nice long shower.

Without Utilities means boondocking. When I'm boondocking I need to conserve water and resources. There I'll use a LPG/Electric/Engine Heat source 10 Gallon water heater. Probably in LPG mode, but the engine heat shouldn't be discounted as it's free waste heat that will warm the water. I'll put a tempering valve on it to limit output to 120 so that I can stretch my hot water supply.

I had a Truck Camper before with a 6 gallon water heater. A shower was very do-able in that if you were thrifty with water. One key is turning off the water. Wet down, turn off, soap up, turn on and rinse, turn back off and soap more and rinse again.

Another neat trick I saw was incorporating a water valve and button to cycle cold water back to the tank and bring hot water to your fixture. That saves a gallon or two at most, but it adds up. Sort of an on-demand recirculating loop. I've priced the components and it's cheap.

Tango · 10-01-2018, 04:34 PM

Interesting. I am looking at possibly installing two water heaters. One LPG for boondocking...and...a small electric when power is available. But they would be plumbed separately with just a couple of ball valves directing the water where needed, as needed.

o1marc · 10-01-2018, 06:42 PM

Comments, pros and con?
https://www.ebay.com/itm/Rain-Man-L1...nd!30534!US!-1

Tango · 10-01-2018, 08:19 PM

Not familiar with that brand so can't really comment. What I do know (from experience) is that the biggest weak point with most tankless is the flow rate. With all but one (that I know of), you have to crank the hot open to a high flow rate or the burner shuts down. Makes for a lot of wasted water. The only unit I am aware of that has overcome that issue is the Excel. It is also "ventless" meaning you don't need to cut a hole in the roof.

https://www.campingworld.com/excel-v...SABEgKfWPD_BwE

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