hot water water on demand with a with a normal water heater

[Frank's Trailer Works]

Okay, This may be one of those left field thoughts, but... well here it goes. Why not have instant hot water without using an expensive on demand unit. In my house the hot water is in a loop and a pump circulates the water so that when I turn on the water, it is hot almost at once. A customer of mine wanted some fancy towel warmers in her bathroom. The plumber, being somewhat of a hillbilly, circulated the water through the warmer without any form of pump. It was like magic... no pump and hot all the time. I think that his clever trick might be able to be used in a trailer... it is so simple that only a hillbilly would know to do it. He ran a line from the heater to the warmer( substitute sink in the case of the trailer) then he ran a line back to the heater and tied that into the drain on the water heater. He replaced the drain with a "t" and connected into that. He created a giant loop to make it simple. This all caused the force of nature called convection current to take the hottest water in the top of the tank and flow thru the pipe to the warmer. As the water cools it actually causes the water to flow faster back to the water heater. It was a very clever solution and very cheap to do. Could this work in a trailer? If a loop was started from the top of the tank, fixtures were "t" off of it and it was to return to the drain on the water heater, would it not circulate? What do you all think?

[overlander63]

Why stop there? Put in a heat exchanger, and have a fan blow across it, creating a hot water furnace. We do this in cars, though with a water pump in the line.
Hot water, and hot air, all without a pump. If you really wanted to do this, I wonder if you could concoct a small radiator, like we used to have in our houses. No moving parts, you could even do this boondocking, and do away with the catalytic heater, and potential for CO poisoning.

[87MH]

Originally Posted by 62overlander

....If a loop was started from the top of the tank, fixtures were "t" off of it and it was to return to the drain on the water heater, would it not circulate? What do you all think?

Three things are wrong with this scenario.....first, in a trailer, unlike a house, the top of the water heater is at a lower elevation than the sinks or shower valves. The second point is that there is usually a charge of air at the top of the water heater. This air charge acts as an accumulator to reduce water hammer when opening or shutting either cold or hot water valves. The presence of this water/air interface complicates a workable convection circulation. Third, the relatively small total system capacity found in a trailer would lead to an excess of cold water circulating from the bottom of the water heater (where the inlet is) to the top of the water convection system (normally the top of the water heater - the outlet) whenever a hot water tap is turned on. This means that cooler inlet water could mix with the hot water coming from the top of the water heater.

Sorry, good idea, but I do not think it would work on a trailer sized system

[SilvrSausage]

Great minds think alike! I was thinking of a hot-water recirculation system from near each hot spigot back to the heater to save waiting-for-it-to-get-warm water when boondocking.

I hadn't thought of a convection system. That would probably work fine in a house with the water heater in the basement; within a trailer it would be hard to get the elevation and slope of the pipes to what it needs to be to develop a worthwhile convection current. Not to mention, the convection method will be circulating hot water out of the heater continuously and uncontrolled. The cooler the weather, the more the heater burner runs, without turning on a single faucet.

I was thinking instead of having a small pump to recirculate the water; this would work well if you have, or would like to add radiant heating now or in the future. The pump could be activated manually when needed, perhaps a button by each hot spigot would be crude but cheap and effective.

If you wanted to get real fancy, you could have it run on a longer or shorter duty cycle, say 30- seconds on, 3-5 minutes off. Increase the percentage of on-time the colder it is.

I was thinking of ways to make the system perform better, to get a longer duration of hot water for showers. One way is to have the water not recirculate to the heater directly, but instead to a (let's just call it) Boost Tank. This is a small (3-8 gallon) tank that should be located near the existing water heater, preferably within the same insulated space. The water heater would draw the hottest water from this tank as its input, and when recirculating intermittently to faucets, the boost tank would become somewhat warmer than ambient temperature, enough to allow a substantially longer runtime than possible when cold hookup (or tank) water is going into the heater directly. Incoming cold water blends with prewarmed water in the boost tank before moving on to the heater. If you really wanted to put your engineer cap on, you could add a small solar loop to the boost tank.

In case you haven't guessed yet, I LOVE overengineering things!
-SilverSausage