LP Gas On-Demand Water Heater

[MisterSandals]

didn't get any response.

You've posted on someone else's thread, its bad form to respond to hijacking as it only encourages it.

New threads are on sale right now, you can create one and have your own area to ask all you want and get answers for all your questions in one place.

 

[Hedges]

<I'll go look for that new thread>

 

[BuffaloTrace]

I built a small 3 ft. X 3ft. Fully enclosed shed shower outdoors with hot water utility sink. I used 1/2" high temp rated CPVC (very cheap) at about an 8ft run from the water heater. Heater is mounted under roof eve and inlet water comes from a T fitting on an exterior hose bib to a flexible stainless braided line into the water heater. For the hot water heater I opted to use an LPG tankless heater from Amazon. There are tons of cheap ones available. Mine was $130+tax shipped. Not the most efficient thing but combined with a $50, low pressure 400btu regulator the heater works better than I ever imagined. I use it every week. It has a very low pressure switch in it and the igniter is powered by 2 x D batteries.

This is a low pressure but high gas flow unit, so 1/2 psi regulator is required.

I cant stress how well this thing works but it's more of an off grid solutuon. I've seen linked together in series as well for more heat on high flow applications. but I use a 1.6 gpm shower head.

Amazon.com

Nice thing about tankless on demand heaters is that it's fairly easy to feed pre solar heated water into the unit prior to LPG heat using a simple solar water heater (to stay on topic)

 

[12VoltInstalls]

a $50, low pressure 400btu regulator the heater works better than I ever imagined. I use it every week.

I have a different brand but use it to shower, wash dishes, daily.
I have it on a rotary timer switch in an RV; the water pump and a 12V>3V transformer are fed by the timer output. I didn’t want to deal with expensive D batteries and it works great. I do have the battery holder and a pair of D’s as a backup but I’ve never needed them. 12V solar supplies the power.

I agree these type units are fantastic. I use a smaller unit and gas use is very very low but I could get 140*F water if I wanted. (I don’t want 140* water….)

Please elaborate on the 400btu regulator. Is this a gas regulator or a water temperature balance regulator?
The unit I bought came with a propane regulator and hose to connect to a 20# cylinder but I made up a copper 3/8 line from the former RV water heater supply and just used the RV regulator.

One recurring problem I have had with these is the water flow switch internal to the unit. It is supposed to activate the ignition and gas valve when water flow occurs (they all have) and when water flow stops gas valve should be closed. 3 units have failed- after six months or so of use you would turn of the shower but the burner would continue to run. Eventually the over-temp/high-limit would cut out but sometimes it would boil water and blow out the plastic RV hot water line.

I think all of these units are a safety concern. It appears that there’s a bunch of different brands with identical appearance, parts, and architecture. I’m not saying don’t use them, I’m saying they need active safety mitigation by the user.
I currently ’solve’ this consistent safety problem with a switch so that when I turn off the shower I can instantly unpower the unit which closes the gas valve. I do that habitually although I have noticed the unit will shut down 50% of the time.

My recommendation is to:
- Provide a convenient power cutoff switch
- Provide a gas shutoff valve at the unit
- always run a “whole house” water filter in-line ahead of the water heater.

Basically my conclusion is that the tiny waterflow sensor is easily gumped up and is most likely to be the cause of failure. It’s not a convenience failure- the gas valve not closing at no-flow is a safety failure! I have had 3 or 4 failures in the past three years, all the same issue. That is a concern!

 

[BuffaloTrace]

I have a different brand but use it to shower, wash dishes, daily.
I have it on a rotary timer switch in an RV; the water pump and a 12V>3V transformer are fed by the timer output. I didn’t want to deal with expensive D batteries and it works great. I do have the battery holder and a pair of D’s as a backup but I’ve never needed them. 12V solar supplies the power.

I agree these type units are fantastic. I use a smaller unit and gas use is very very low but I could get 140*F water if I wanted. (I don’t want 140* water….)

Please elaborate on the 400btu regulator. Is this a gas regulator or a water temperature balance regulator?

One recurring problem I have had with these is the water flow switch internal to the unit.

Eventually the over-temp/high-limit would cut out but sometimes it would boil water and blow out the plastic RV hot water line.

My recommendation is to:
- Provide a convenient power cutoff switch
- Provide a gas shutoff valve at the unit
- always run a “whole house” water filter in-line ahead of the water heater.

Basically my conclusion is that the tiny waterflow sensor is easily gumped up and is most likely to be the cause of failure.

I've had mine running outdoors bolted onto the outside of the building up about 5ft off the ground, partially protected by an overhanging eve from the house that the lean-to bathroom is up against. So far I havent had any problems (havent even had to change the D batteries either)

The Regulator I speak of is a low pressure, LP regulator as required by the manufacturer, I seem to remember the specifications being in Pascals in the manual which is long gone. But it's a 2 stage 400 btu regulator, so at low pressure it has the high volume needed for the heater to work well, unlike those small low pressure low btu pin hole type regulators used for outdoor grills and lp stoves and ovens. I have the regulator screwed directly into the main valve on a 30lb (5 gal?) Propane tank which sits off the ground on a stand.

I can see there being faults on these as the price at $135 seemed too good to be true after I got this thing working so well but I run mine easy, never have I maxed out the 20 minute run time. Mine will automatically shutoff at 20 mins.

Sounds to me to you your heater set too high if you're blowing lines. I use the high temp type CPVC as it was the least expensive option, its glued (welded) together with the Christie's red pvc solvent based glue, which might work better for lines which are close to the heater. Directly on the heater I have braided stainless lines that run to the inlet and from the outlet to threaded cpvc fittings.

I like your recommendations, and I can see these units as having multiple failure points depending on manufacturing tolerances as well as use case, but damn the price was good and it worked out. Considering you can buy multiples of these for the price of some of the larger units. Installing one in the basement of a class A RV was also pretty straightforward.

 

[12VoltInstalls]

Sounds to me to you your heater set too high if you're blowing lines.

Did you read what I said? The burner wasn’t shutting off and was boiling water and the pressure went up. (Other reports online mention solder running out of the units.)

When operating the water is 103-ish because I have yet to develop a tolerance for 212*F water.

My point was these not-UL listed devices need a level of respect because they don’t always fail safe.

 

[BuffaloTrace]

Did you read what I said? The burner wasn’t shutting off and was boiling water and the pressure went up. (Other reports online mention solder running out of the units.)

When operating the water is 103-ish because I have yet to develop a tolerance for 212*F water.

My point was these not-UL listed devices need a level of respect because they don’t always fail safe.

I see. Agreed on the respect needed. In a residential setting on a permitted structure I wouldnt think of using one, not because of safety, as I dont have the same experience.

What pressure regulator are you using? Have you tested that its operating at 1/2 psi or less?

After I converted the pascals on my heater I believe it ended up being roughly
Closer to 0.4 psi, but closest I could get was a 1/2 psi lp reg.

I will also note that I do have high water pressure to the inlet. This may be helping keep the valve clean and free of debris, I am not using a filter, but after reading your suggestion, I am going to add one.

 

[12VoltInstalls]

What pressure regulator are you using? Have you tested that its operating at 1/2 psi or less?

A standard RV post regulator currently but I did run the first one on the regulator supplied with the unit which worked fine for six months+ with only one refill tank in that time. When it failed I bought another and when I installed it i used the camper propane lines for simplicity and no unsecured propane tank to steal.

The point you are missing is that they all run fine. The water flow sensor is what is failing every time. I have about 38psi with the pump running and waterflow volume exceeds the minimum by 100% (I’m using the onboard water volume control and the shower head supplied by the manufacturer with the unit. One would assume those are acceptable. The kitchen sink will flow 2 gals/min but the showerhead thankfully is much less)
Backflushing often ‘fixes’ it but only for a short time. The flame is a beautiful blue when running with appropriate crisp edges. I’m sure the gas pressure is fine; running is not the problem, water flow and pressure is fine.

My point was for people to be aware and watchful with these chinese not-UL listed products as in my opinion an unarrested flame is a fire hazard and a scalding hazard. Hard mechanical shutdown is a safe state to assure nothing happens to this fault-prone water heater that otherwise works very well.

 

[Hedges]

My home water heater has a gas valve which is switched on/off by a thermocouple.
Valves like this are fairly interchangeable between brands. Requires separate thermocouple. May be for natural gas only, not propane, but not sure why.

Amazon.com

Gas stove has similar. A redundant shutoff for gas supply would make the water heater safer. I think moisture or contaminants can jam the valve. I saw one that opened once, didn't close again (had been open to atmosphere, unprotected). Another valve ran for decades without problems.

 

[BuffaloTrace]

A standard RV post regulator currently but I did run the first one on the regulator supplied with the unit which worked fine for six months+ with only one refill tank in that time. When it failed I bought another and when I installed it i used the camper propane lines for simplicity and no unsecured propane tank to steal.

The point you are missing is that they all run fine. The water flow sensor is what is failing every time. I have about 38psi with the pump running and waterflow volume exceeds the minimum by 100% (I’m using the onboard water volume control and the shower head supplied by the manufacturer with the unit. One would assume those are acceptable. The kitchen sink will flow 2 gals/min but the showerhead thankfully is much less)
Backflushing often ‘fixes’ it but only for a short time. The flame is a beautiful blue when running with appropriate crisp edges. I’m sure the gas pressure is fine; running is not the problem, water flow and pressure is fine.

My point was for people to be aware and watchful with these chinese not-UL listed products as in my opinion an unarrested flame is a fire hazard and a scalding hazard. Hard mechanical shutdown is a safe state to assure nothing happens to this fault-prone water heater that otherwise works very well.

Yea sounds like you diagnosed everything. They are simple units, not particularly efficient either...but the price and simplicity of the unit is what originally got me to research them, and read through all the amazon reviews, which were surprisingly good. I did see some others having issues with the water flow switch, under what I assumed was low pressure but never saw anything about a melt down like you described.

I'm going to keep my eye on that flow switch now, and I just ordered an inline hose filter as my unit is fed from a standard hose bib. It isnt a whole house filter but as a precaution.
I dont use it much, now maybe once a week at the moment, but for almost a year after first installing it got used everyday. Crossing fingers I dont have the same problem as you.

With my unit I have the gas flow knob turned down 1/3 setting so that it cant flow enough gas to scalled. That being said flow rate of the water has a lot to do with how these simple units operate. Lower flow rate, will mean more water heat, while higher flow rate will be less. I have the flow rate knob on the unit open as much as it can go as to max out the flow rate of the unit itself. I always have the summer/winter setting set to winter as the only point of that knob is to shut down 2/3 of the burner surface area which seemed odd and less efficient as the water will run through all of the heat-sinked copper tubing regardless.

 

[BuffaloTrace]

My home water heater has a gas valve which is switched on/off by a thermocouple.
Valves like this are fairly interchangeable between brands. Requires separate thermocouple. May be for natural gas only, not propane, but not sure why.

Amazon.com

Gas stove has similar. A redundant shutoff for gas supply would make the water heater safer. I think moisture or contaminants can jam the valve. I saw one that opened once, didn't close again (had been open to atmosphere, unprotected). Another valve ran for decades without

My home water heater has a gas valve which is switched on/off by a thermocouple.
Valves like this are fairly interchangeable between brands. Requires separate thermocouple. May be for natural gas only, not propane, but not sure why.

Amazon.com

Gas stove has similar. A redundant shutoff for gas supply would make the water heater safer. I think moisture or contaminants can jam the valve. I saw one that opened once, didn't close again (had been open to atmosphere, unprotected). Another valve ran for decades without problems.

These bargain tankless heaters use a water flow switch which activates a piezoelectric electric igniter run by 2xD batteries. I have not opened mine up as I have yet to have problems but I'm assuming the same flow switch also opens the gas valve, how it does this I am not sure, when water stops flowing the gas valve is supposed to close. It is also supposed to automatically close after 20 minutes of continuous run time, which mine does as I've tested this with a particularly long shower.

 

[12VoltInstalls]

I'm assuming the same flow switch also opens the gas valve, how it does this I am not sure, when water stops flowing the gas valve is supposed to close.

I believe the flow switch closes and both signals the ignitor and provides milliamperes to the gas valve.
If you either open the battery door (or kill the 3V power supply I’m using) thereby interrupting power the flame immediately extinguished. The high limit safety switch opens the circuit to the gas valve as well. I ‘think’ there also is a proofer to open the circuit to the gas valve if the burner does not ignite.

 

[BuffaloTrace]

I believe the flow switch closes and both signals the ignitor and provides milliamperes to the gas valve.
If you either open the battery door (or kill the 3V power supply I’m using) thereby interrupting power the flame immediately extinguished. The high limit safety switch opens the circuit to the gas valve as well. I ‘think’ there also is a proofer to open the circuit to the gas valve if the burner does not ignite.

Aah so it's being controlled by the hydro switch and powered by the 3vdc power source. There is definitely proofer, I am on my 3rd or 4th tank swap now and have had the tank drop so low that it would not ignite. the igniter would try for a good 20 or 30 seconds than stop, though I DID have a feignt gas smell, much like around a standard household water heater prior to ignition, it was such low pressure in the empty tank that no ignition, but no gas flow after igniter stopped, so I never worried about it. Being that my setup is all outside I couldn't be happier. My neighbor and I installed one in a vented Class A RV basement in place of the old water heater. Its a small one, only 6L I think, but the owner uses ultra low flow spigots including shower head and seems to like it compared to his old tank furnace...hes a boondocker and doesnt like the idea of the hot water being heated all the time as was the case with his original unit. Saved himself a small amount of weight and basement space as well.

 

[12VoltInstalls]

Saved himself a small amount of weight and basement space as well.

The thing that crossed me mind is the clearance in a confined space. This was a vented/piped exhaust I assume?

Mine is sold as ‘outdoor’ so no ‘vent’ chimney. This past spring I mounted it inside on a wall with 20” overhead and 12” each side. The ceiling doesn’t get hot; warmish after a shower, never hot (or I would have not kept it there). So in winter that makes it 100% efficient lol

As far as efficiency, while people say these are not ‘efficient’ as far as the heat exchanger function I don’t look at it that way. An RV 5-gal water heater uses way more propane than these do in a month, and you can run an RV tank water heater out. This unit will run ‘forever’ at several gallons/minute rate - never runs out. If I’m gone a week it uses zero propane. That’s efficient in my mind- it costs 25-35% what the RV water heater costs for the same use.

EDIT: Fun facts on trying stupid things:
I know a guy that that’s a propane tech and system designer. He uses one of the bigger units as a whole-house heater for baseboard hydronic heat and another for hot water into a super-store. In the coldest months it can’t keep up by itself but they have a tiny woodstove in the kitchen and a big pellet stove. (he has a small pellet mill and manufacturers enough pellets to make his pellets and cordwood free)
The cheapo propane heater keeps the bedroom zones 70*F+ because the kitchen and living room zones don’t call with the pellet stove going. When they’re gone it will hold at 60-62 at 0*F outdoor over a weekend. He estimated that this cheapo setup saved them 20% of annual propane gallons versus the old whole-house system and was $6K less than a real furnace. He had the money for a furnace but thought he’d try it. I think it’s been five or six years successfully. Last we talked on it they still have the money set aside for the furnace but they’re not going to do it unless they decide to sell.
The flow valve issue doesn’t effect him because it only gets power when the circulators call.

 

[BuffaloTrace]

Mine is sold as ‘outdoor’ so no ‘vent’ chimney. This past spring I mounted it inside on a wall with 20” overhead and 12” each side. The ceiling doesn’t get hot; warmish after a shower, never hot (or I would have not kept it there). So in winter that makes it 100% efficient lol

Yes, the 2 that I have personal experience with are direct vent out the top. Mine has a round chimney exhaust out the top, didnt use, just covered it for some rain protection with a stainless shelf. The smaller one (used in RV) had a rectangular exhaust on the top, we used a steel rectangular 90 dg vent to redirect the exhaust out the side vented area from basement that the original water heater used.

I suppose by efficient, the amount of heat generated by the gas that's actually transferred to the water. I do know my neighbors RV uses way less propane now because like you said he isnt trying to heat 3 or 4 gallons of water all the time. In that respect hes saving gas.

I really like the idea of using these on other RV or shed projects and probably will in the future. I'll be helping another neighbor use one for an outdoor shower setup, hes just going to use this In-line with no cold, and have it adjusted to the temp he wants. Again well probably just use one of the smaller ones for that, but the 18L model was overkill for my 1.6gal/min shower head.

 

[SolarPrep]

This thread has bounced around quite a bit, so just some general comments on techniques I've used with good results.

Buy good quality heating equipment. The Takagi units that Steve mentioned are widely used for heating water in car washes, and other tough service areas. They are very robust.

Gas service lines: super easy, just look on one of many published charts, and find the line size that will delivered enough BTU. You have to measure the pipe, tally up the fittings, etc. For example, an elbow can be the same as 5' of straight pipe in equivalence. This same approach goes for venting, and fresh air intakes. Don't cheap out, if you are at the limits, bump up to the next size. ( For venting, you do need to maintain a certain velocity, so just going bigger is not always better) Don't use conventional white teflon tape to seal gas threads. Get the yellow stuff, or better yet use a good sealant like Gasoila.

For ball valves, physically look inside the valve and see what size the actual hole is. It can be shocking to buy a 3/4" valve and then see that the port size is less than 1/2". Buy full flow valves. Less restriction.

If you are pumping, restriction is a big issue. It isn't just about distance, it is about elbows, adapters you use, pressure drop across a 3-way valve, etc. One of the reasons I use Wirsbo PEX is it maintains full size through the fittings, due to expanding the tubing. Many others crimp the tubing on, and reduce flow. I used to install a lot of Honeywell 3 way valves, but have now switched to Caleffi because of their improved flow. (reduced restriction) You should take these factors into account when sizing pumps.

If you are doing a return line for hot water, it doesn't not have to be the same size as the feed line. You only need to move a little water. Old timers would sometimes have a gravity return, which can work fine if properly done. I prefer to pump, and use the smallest one available. I picked up a 1/40hp bronze pump at a Goodwill store NIB for $10. You can put one on a timer if you like, and just have it come on periodically and move water around the loop.

Insulate the heck out of your tanks. Insulate hot water lines. I still have not done that on my delivery lines, and hope to get around to it sooner, rather than later.

There are some nifty units available that combine some of these functions into one device. Caleffi, Grundfos, etc.

If you are piping in copper ( I still like soldering, believe it or not) make sure you ream the cut pipe. It has been proven that over the course of a typical house, the ridge left inside the pipe can drop the effective flow rate for 3/4" pipe to nearly 1/2".

I have become a huge fan of the Grundfos Alpha 2 pumps. They are extremely efficient, and long lasting.

Wasting water is a bad habit that needs to be changed, not just based on an economic payback scenario. With the advent of PV, it looks like a lot of people will just keep adding panels, and not change their consumption habits. I'm not preaching here, but am trying to be a better steward of available resources. It makes me smile to look at one of my new pumps and see that it is using 18 watts, instead of the old one that used 90 or more.

 

[BuffaloTrace]

I agree with all of the above. Insulated soldered copper pipe is the best, but costly and more difficult to work with. Over sizing gas and water lines is also an example of future proofing, can help with different future appliances as well as water services (muni vs onboard/pumped). Water pressures vary drastically for even muni services based on slight elevation increases.

My uncle uses a Grundfos 2hp pump in his jury rigged lead acid solar/wind powered well and it has functioned flawlessly for several years. He doesnt use very many panels, but combined with his windmill and diesel truck sized batteries (diesel mechanic), hes never had any down time. His system is basically as good if not better than muni water and his Grundfos pump was the last component in getting his system reliable on his lower power productio. system.

 

[12VoltInstalls]

Wasting water is a bad habit that needs to be changed

Wasting water is subjective and regionally defined.

I get sensitive about that because of some ‘local’ attitudes regarding aquifers and “the world (is) running out of water.”

Here, we had a very dry spring and summer. Some shallow wells did dry.
Though water just runs out of the ground here. Up behind me there is a ‘small’ mountain ridge and I’m pretty close to the steep rise to the peaks. Before it started raining again the two brooks and multiple seeps up on the hills near the ridge were still running. Slower, but constant water flow.

You can’t put a cork in them. Totally unconcerned with ‘wasting’ that water. Local records say these hills have been wasting water for hundreds of years. The problem? State law has made groundwater, dug, and ever-running surface springs and wells illegal “they’re not safe.” So people have to have a $12,000 (or more) 3-gal/minute well drilled instead of using the 20 gallons a minute running out of the earth that’s available in so many places.

/rant

 

[SolarPrep]

Wasting water is subjective and regionally defined.

I get sensitive about that because of some ‘local’ attitudes regarding aquifers and “the world (is) running out of water.”

Here, we had a very dry spring and summer. Some shallow wells did dry.
Though water just runs out of the ground here. Up behind me there is a ‘small’ mountain ridge and I’m pretty close to the steep rise to the peaks. Before it started raining again the two brooks and multiple seeps up on the hills near the ridge were still running. Slower, but constant water flow.

You can’t put a cork in them. Totally unconcerned with ‘wasting’ that water. Local records say these hills have been wasting water for hundreds of years. The problem? State law has made groundwater, dug, and ever-running surface springs and wells illegal “they’re not safe.” So people have to have a $12,000 (or more) 3-gal/minute well drilled instead of using the 20 gallons a minute running out of the earth that’s available in so many places.

/rant

Hey, I agree with you. My comments are aimed more at the very common situation in millions of households where you turn on the shower, and wait for a minute to get hot water. It truly adds up. And, the vast majority of that water is coming from municipal water systems, not free flowing surface water.

I've owned a lot of buildings in my lifetime, and nearly all of them suffered from this. Some of them were 8-plexes, and that really adds up.

I've also (at times in my life) bought into the bigger is better paradigm. I regret that. I'm trying to be cognizant of how my actions affect others, my own financial situation, etc. And, just trying to help a few other make wise choices.

 

[BuffaloTrace]

For the these low pressure on demand LP water heaters, a regulator that is under .5psi. The instructions though not extremely easy to understand, do specify the pressure in pascals, which I believe converted down to .4psi.

I originally tried a small camp stove regulator but it had a pin sized gas hole in it, only obtaining around 100k btu or less.

For my outdoor shower setup I used this 2 stage regulator. Works flawlessly.

https://www.etrailer.com/Propane/MB-Sturgis/108220.html