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Old 02-25-2008
Rose Mary's Avatar
Rose Mary Rose Mary is offline
Senior Member
Join Date: Jan 2008
Location: tenmile oregon
Posts: 342
Default on demand tankless hot water heater

Hi group
one of the issues I will be working on when I get home is the hot water heater.
Has anyone installed the tankless on demand? In theory it sounds great, energy efficient etc. plus when dry camping wouldn't need to run the genny to heat shower h20...

would it fit in the location of the present hwh? under the bunk in back by..
I understand it would need vented to the outside like the furnace...

Rose Mary
presently in Bandon by the Sea
only 60 miles from home
after some agate hunting this morning we will be home for the first time in 3 months....

Rose Mary
82 turbo FC 35
JP's White Bird
SW Oregon
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Old 02-25-2008
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peteaeonix peteaeonix is offline
Former Bird Owner
Join Date: Jan 2008
Location: Ridgefield
Posts: 2,010

I have the AquaHot system --- which is, essentially, a tankless hot water system -- it provides both domestic hot water and hot water used in the hydronic heating loops (as well as engine preheat for cold weather starting). It uses diesel (fuel oil) instead of LP gas.

On the whole, I'm satisfied with the system. It provides significant amounts of hot water--far more than an 8 or 10 gallon tank-type system could produce.

However, a tankless system actually only increases the heat of the water as it comes though the system. So, if it heats the water by 30 degrees, then water entering at 70 degrees will be a pleasant 100 degrees, but 50 degree water will still be a chilly 80 (for a shower). This is hypothetical as I don't know exactly how much the A/H actually heats the water (and the initial flow, once the hot water has reached the faucet, is well above 120 degrees) -- but realize that the colder the water is at the start, the colder it is when it hits your body in the shower.

A side effect of the A/H system, that might not be present in a true tankless system, is that the tubes in the A/H store some quantity of water, so the initial effect is like having a modest-sized hot water heater. Depending on the input water temperature, once the initial quantity is used, the water temperature can drop rather dramatically. I soon learned that the system delivered very pleasant, almost limitless length showers in Texas during the spring, but lingering too long during December in Denver was not very practical.

For installation, you'd need to ensure that the venting system could be accommodated. Personally, I wouldn't feel too comfortable with a source of CO2 or CO directly under the bed (to say nothing of the heat that needed to be dissipated). While the vent would handle the exhaust gasses, I'd prefer to find a location where a failure in the venting system wasn't at all likely to direct exhaust gasses into the living area, especially in a bedroom.

I note that the A/H in my coach is approximately below the dining table in the basement compartment. The exhaust exits under the side of the coach but any combustion products that escape into the basement are most likely to drift out through holes near the sewer hook up (nearby) than to penetrate through the floor (that's pretty well sealed).

I'd also suggest looking for RV-certified units. There are many home-type tankless systems that might appear attractive, but they may not be able to handle the vibration of over-the-road travel.

Pete Masterson
(former) 95 WBDA 42'
(now) 2011 Roadtrek RS-Adventerous
Ridgefield, WA
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Old 02-25-2008
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RGloverii RGloverii is offline
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Join Date: Jan 2008
Location: Linden, MI
Posts: 1,556

Just to chime in on the topic...

I have a true tankless natural gas water heater in my home, and I can tell you it's an amazing product. I have a digital panel mounted in my kitchen, which indicates the temperature it's st to achieve, and I can raise and lower that temperature with the press of a button. In my household, it is saving me about 1/3 on natural gas versus the original tank style heater.

As for its ability to heat cold water, there are different models out there that have different 'heating' capabilities. For the most part, however, even the cheapest would be able to make the coldest water hotter than 130 degrees.

That being said, I would NOT recommend putting one into a motorhome. Reason why? They use a TON of gas (natural gas in my home, LP in a coach) when they are actually in use. The unit will consume zero gas when you're not using hot water, but as soon as you turn on a faucet, trust me, the gas is flowing hard! I just really doubt the LP tank on a coach would be able to support a tankless unit for very long.

Take that with a grain of salt, cause I never looked at specs for a RV tankless unit. Just going from my experience at home, I don't think it would be practical. I would think the Aqua Hot or Primus systems would much better suit your needs.
Robert Glover, II
91 SP36
Linden, Michigan
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