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-   -   Flash Boiler with Used Tankless Heater Build (http://www.homebrewtalk.com/f51/flash-boiler-used-tankless-heater-build-197179/)

PaulHilgeman 09-23-2010 11:21 AM

Flash Boiler with Used Tankless Heater Build
I got a free 10 year old tankless heater, old for sure, but very little use.

So far, I have disassembled everything and have the burner solenoids controllable and the ignition system working.

I have a few questions. As far as the burner goes, it was origianlly a NG burner, will LP work the same as long as I keep the PSI real low, at least for testing? I suppose I can always throw a regular burner in there if it doesnt work.

Second, the heat exchanger is 10 passes, about 6" long of 1/2 inch copper pipe through a series of about 75 1/32" thick copper plates. I guess time will tell if this is enough.

Has anyone else done this? Would seem to be an easy way to get some parts to find one on Craigslist.


PaulHilgeman 09-26-2010 01:24 PM

well, This doesnt just work well, it works perfectly.

I set-up the system at 1/2 gal per minute and fired the burner up, after about 10 seconds, I was getting just steam out of the outlet and I got scared and shut it all down.

After some tweaking to get to the magic 170 degree mark at the output, I measured the flow rate at 2 gal per minute, maybe a hair over.

This was with 68 degree input water.

I will post some pictures of the build shortly, but I think the key is to have as much surface are in contact with the flame as possible, and the forced-air blower provides a ton of O2 for the burn.

The only problem with the propane is that I am getting a little soot in the exchanger, but I probably ran about 50 gal through it yesterday when i was testing, equivalent to probably 6 5 gal batches.

kladue 09-26-2010 04:45 PM

How much control of the fuel flow do you have?, enough to reduce the flame to a point you can do fly sparge water heating at a low flow rate?. IMHO the flash boiler is the only way to go, makes it possible to get started in minutes from a cold start, and with flame level control you can do fly sparging and steam injection RIMS.

cascadia 09-26-2010 05:20 PM

Very intriguing. Can you post some pictures? Thanks

PaulHilgeman 09-26-2010 11:28 PM

I'll post some pictures tomorrow.

Sure, I am sure all it would take is some regulator on the gas input, The one I have is from a propane heater that had a regulator piped in on the equipment, so I wasnt able to salvage it. Eventually, I will upgrade to a regulator on the propane side, but for now, I am a batch sparger, and this is perfect, I can just adjust flow rate to get everything right.

MacBruver 09-26-2010 11:36 PM

Wow... 100F delta at 2gpm... that rocks! Very interested to see more pics of it.

PaulHilgeman 09-27-2010 12:52 PM

Ok, so here we go:


Here is a shot of the very dangerous test run, you cant see the thermometer, but that is 170° water coming out, 68ish° coming in. This is a good example of mixing, Fire, Water and Electricity. The GFCI tripped right after I took the photos, which closes the solenoid valves for the gas.


This is a basic shot of the front of the unit. I sprayed it all white, the left switch is a 25A DPST switch, flipping it up sends rectified and smoothed AC to the solenoids to open them up, and sends unrectified AC to the motor to get the blower running. Assuming gas is hooked up, it starts flowing. Next to the right is a simple push button switch that feeds 120V to the ignite (generates a spark above the burner) to ignite the LP.


This is the guts of the unit, you can see my wiring in the lower left, from the bottom to the top, you can see the blower housing with the solenoids, above that, the burner chamber, followed by the heat exchanger.

It has 3/4" NPT inlets and outlets, I plan on reducing these down and putting quick-disconnects on them, that way if I ever want to use it after the sparge, I can really bring things to a boil quickly by pumping my sparge through it.

weathejx 09-27-2010 02:14 PM

very cool

Jawbox0 09-27-2010 03:39 PM

How sensitive do you think it will be to the Input water temperature? I'm not totally clear on the specifics of temp control in these things?

skinydipper 09-27-2010 03:49 PM


Originally Posted by PaulHilgeman (Post 2294184)
I have a few questions. As far as the burner goes, it was origianlly a NG burner, will LP work the same as long as I keep the PSI real low, at least for testing? I suppose I can always throw a regular burner in there if it doesnt work.

You need to change the orfice from NG to LP, the orfice sizes are different. I don't remember which way, but I believe the NG orfice is smaller than the LP orfice so you may be able to reem the hole to the correct size.

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