Tankless water heater for heat?

idamanzz

New member
Hi gang,
Has anybody considered using a commercial tankless propane water with power vent heater for hydronic heating? They are commonly used for this purpose in houses. Im considering using one in place of a Espar or Webasto. (possibly cheaper) Pump coolant through it, use water(coolant)/air heat exchanger for cabin heat. Run a loop for engine pre heat. Water (coolant)/Water (domestic) flat plate heat exchanger for hot domestic water.
Any thoughts? Thanks!
 

Carlyle

Explorer
Sounds like a nice idea to use for engine pre-heat. I understand that they are a problem if they freeze though and that was the major factor that kept me away from it.
 

kerry

Expedition Leader
I'm pretty sure some European motorhomes use that kind of system. I had a motorhome with a small Paloma tankless for hot water and I loved it. I think there is no need for a powervent. Mine was either vented thru the roof or out the side but definitely not power vented.
 

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Co-opski

Expedition Leader
Yes, a 50/50 mix with anti-freeze and h2o would help keeping it from freezing, like in your cooling system. I like the idea keep use posted.
 

pskhaat

2005 Expedition Trophy Champion
Tankless LP/propane water heaters use a LOT of energy like rated 100,000s of BTUs. You might get a way with less volume for propane but likely not that much less. I don't remember the volume/pressure figures off my head.

Additionally they require a substantial amount of flow in order to trigger the ignition and a really good circ pump would be necessary. The temp rise rate is quite substantial too so I don't know what type of effect that would have on coolant.

You might have to check out getting a very small one, are you thinking something like this http://www.houseneeds.com/shop/HeatingProducts/WaterHeating/rv/rv500waterheatermainpage.htm
 
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SicNick

Observer
any updates on this, I really like the idea of having a heater that uses antifreeze like the one in your vehicle, with the added benefit of keeping the truck warm on sub freezing nights.:coffeedrink:
 

dzzz

You will need at water to water heat exchanger, which is not "tankless" for hot water.
I would never use a home product for heating water in an RV. It probably wouldn't last long, and is potentially dangerous.
I'm going to do this type of heating, unless I'm way over budget. I believe earthroamer does it this way.
The antifreeze loop runs through the engine and also a 6 gal water to water heat exchanger in the cabin. The espar hydronic is in this loop.
Fresh water is heated in the heat exchanger.
After driving, there's always hot water available without the espar running. When the coollant water is cold, the espar heats it. Either for engine warming or hot water. But for camping in winter, it is desirable to prevent heated water from entering the engine. So Controlling water circulation is the issue. Add a water to air heat exchanger for camper heat, and it gets more complicated.
An easier way is a multizone boiler made for large RV's. The smaller one I've seen has four pairs of inlet/outlet. Four zones. I would use one for engine warming, one for hot water, and two for cabin heating.
Both the espars and the RV boilers can be diesel fired.
 

mhiscox

Expedition Leader
Both my Unimog and the Sprinter campers have on-demand propane-fired hot water heaters, I like them a lot and think it's a good way to go. The Sprinter unit is a $1500 marine unit that works extremely well (as it should for the price), whereas the Unimog has a $300 wall mount unit that has less capacity that I bought off of eBay. It works well, too, but the performance is more dependent on inlet water temperature. You can only get a big temperature increase if you cut the flow.

Both of these, however, are self contained, which is one of their advantages. Three or four connections--cold water in, out water out and a propane line, and 12V on one (the other's ignition is a 9V battery)--are all it takes. No tie in to the engine, so no "free" hot water, but these systems are both easier installations than engine heat exchangers and have less to go wrong than the diesel-fired heat-exchanger alternatives.

The EarthRoamer Jeep, however, does have an IsoTherm setup for engine-sourced hot water. It works well, but the drawback is the big cylindrical hot water storage tank, which may or may not be an issue in any particular situation.
 

jesusgatos

Explorer
I'm going to use two Takagi TK3 tankless water heaters in my Deuce. One of them is going to be used to heat fresh water, and the other is going to be used in a closed-loop (anti-freeze) for radiant and forced-air heating. I know I could have just used one water heater and a heat exchanger, but it wouldn't have saved much/any space and this way I have a backcup. They'll each suck down almost 200,000 BTU's when they're on full-blast, but they can also 'simmer' down to 11,000 BTU's. These are top-of-the-line tankless water heaters but they're designed for residential applications; so the mfg cannot officially endorse using them in mobile applications. With that said, they (Takagi) has installed these water heaters in a lot of emergency vehicles for the US government (fire trucks, disaster relief, etc.). I don't know how they're going to work out, but I'm going to give them a whirl. Precision Temp makes the only RVIA-approved tankless water heater that I'm aware of, but it costs $4600!
 

dzzz

Good find. Precision temp has a $1000 unit as a direct tank replacement. But I bet the Tagaki is better made. RV specific products that aren't made for boating usually seem cheap to me. At least in the U.S.
 

dzzz

The EarthRoamer Jeep, however, does have an IsoTherm setup for engine-sourced hot water. It works well, but the drawback is the big cylindrical hot water storage tank, which may or may not be an issue in any particular situation.
Does earthroamer have the espars above or below the floor? I'm hesitant to run diesel lines into the camper, although my concern is probably not rational.
 

jesusgatos

Explorer
Good find. Precision temp has a $1000 unit as a direct tank replacement. But I bet the Tagaki is better made. RV specific products that aren't made for boating usually seem cheap to me. At least in the U.S.
Yeah, but if you being able to use a tankless waterheater for radiant and forced-air heating was half of the appeal (to me). I did buy a couple of forced-air heaters from Precision Temp. They're a lot more reasonably priced than their water heaters. The only thing I have left to figure out is the heat exchanger, so that I can tie-into the engine's coolant. Mah Deuce doesn't have a heater in the cab, so I'm thinking that I might make a heater out of a plate-style heat exchanger by putting it in an enclosure and adding a fan.
 

dzzz

Precision temp RV-500 is about $1000 with the vent fan. The advantage of the unit is that it using out side air for combustion. You can't fire up a tagaki in a small tight space without providing air.
 

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mhiscox

Expedition Leader
Does earthroamer have the espars above or below the floor? I'm hesitant to run diesel lines into the camper, although my concern is probably not rational.
Well, if you're concerned about the diesel, you probably won't be excited to know that the cabin heating unit, installed in the bottom section of the storage rack,, is petrol-fired. :Wow1:



You can see the circular vent for the heater output cut into the black bottom panel.

I've studied it, though, and can't see any problem areas. I'm content that it's a good safe installation.
 

jesusgatos

Explorer
A lot of the military trucks have diesel-fired heaters mounted inside vehicles. They pull fresh air from outside the vehicle, dump the exhaust back outside the vehicle and the combustion chamber is sealed-off from the inside of the vehicle. Same thing with a lot of tankless water-heaters. I don't see a problem.
 
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