Dale's Two Tank hot water System - Quick start up and achievement of desired temperature. Easy control of maximum temperature.

Wood fired hot water systems are often less than ideal due to these 2 factors.
1. Heat up time - Due to the quantity of water involved,it can take an hour for the system to attain suitable temperatures for bathing, dish washing etc.
2. Dangerous overheating – If the tank has no means of controlling maximum temperature, the quantity of fuel used for a given firing must be quite accurate in order to not exceed the desired temperature. Anything over 140 F is considered dangerous for domestic use.

This simple plan addresses both concerns while needing no electrical components, or special monitoring equipment.

1. Heat up time. In a one tank system where we want to heat up a large quantity of water, it can take a long time. I would like a 50 gallon system. A system that heats only 5 gallons will reach the desired temperature in a very short time given an equivalent heat source , so this is the size I've chosen for sake of illustration. This tank can now be connected to another much larger tank by means of two short lengths of large diameter pipe, one at the top and one at the bottom of the 5 gallon tank. Thermostats prevent interaction between the tanks at first.

Anyone familiar with automobiles has heard of the thermostat which allows water to move to the radiator once the water jacket around the engine reaches operating temperature. This system works in a similar way except that no pump is used. These thermostats open and close according to the temperature of the water and are available in a wide array of temperature settings.

Suppose we want to produce water no hotter than 140F. A thermostat of that rating could be placed in the pipe leading to the secondary tank. It would only allow the water to thermosiphon between the two tanks when the temperature reaches 140F. This means that the system could not overheat and it would have a far shorter lag time between start up and a point in time when 5 gallons of hot water is available. This is plenty of water for cleaning the dishes, hand washing etc. and would easily be available in the time it takes to cook and eat the meal. The 5 gallon tank is connected to a 45 gallon tank. It takes considerably more wood to heat up this much water, so it would be a simple matter to stop feeding the stove as the desired temperature is reached. In order for the system to be idiot proof, I intend to have it open to the atmosphere so that steam pressure can never build and to put a thermostat on the outgoing tap, so that dangerously overheated water cannot be used by unsuspecting guests. Should the system be overheated, it would be necessary to either wait for it to cool or to run cold water into the system to bring it back to a safe temperature. The safety thermostat at the spigot would then open, allowing water to be drawn off.

This water heating system is to be part of a multifunctional cooking and heating system as described in - Dale's Rocket Mass Heater/ Grill/pizza oven/Hot Water Heater – One appliance does it all. http://www.permies.com/t/19603/stoves/Dale-Rocket-Mass-Heater-Grill

Dale ; Your use of an automobile type thermostat to regulate domestic water flow is revolutionary ! By volume to be heated, and because
it's open to atmospheric pressure you have protection against '' BANG- SQUISH! However once the water has come up to temperature ether within the 1st or the 2nd tank
a very simple mechanically operated (by-metal?)control dial-in system (which is existing technology,) can be used to deliver water at any preselected temp
This is a common over-ride system in hotel/motels , this mixes with much cooler water to provide almost any safe pre-selected temperature !
This is usually a mechanically operated dial-in system that should be hidden from idiots in a locked sealed cabinet, otherwise it is still existing technology.

This is only a little more complicated than the mixing valves of a standard washing machine, mostly in the re-build.
If you have the electricity to 'run' 1 set of washing machine type mixing valves, a redundant set or sets should give you the flow and the temps. that you want !

There is a commonly used Field hot water system where you self regulate the amount of hot water you drain off of pre existing pre-heated hot water,
this works by a system where the cooler water that is added to the volume of pre-heated water, is delivered to the bottom of the container,
causing a directed /ducted over flow of hot water off of the top off the container , this overflow happens before any mixing of waters of different temps. can occur !

I hope that i have explained my points clearly enough to be useful to this dialog ! Be Safe , Keep Warm , PYRO - Magicly yours , - Allen L.

It's a tempering valve, some times the words just won't come ! Thank you - R. Scott

You can put a LOT more heat into water than you realize. My little woodstove already heats all the hot water for my family of THIRTEEN. In fact, we have to make sure to do warm or hot laundry just to draw down some of the HOT water when it is cold. It regularly gets my 50 gallon electric tank over 175 because it trips the overheat breaker on the upper element and I have to reset it in warm weather when we aren't burning wood. I have a tempering valve to bring the outlet temp back down to 125ish (safe for kids but still makes a good hot shower).

Thank you Allen and R. --- Is there a version of these valves that work without electricity ? This building will not have power at first and I just like to pare things down to the bare bones in order to reduce dependence on anything likely to fail. The Idea is to live as luxuriously as possible with as little reliance on high technology as possible. Of coarse if I do give the building electricity, I'll definitely wire the place for sound so that I can listen to music while I watch movies from the comfort of the hot tub where I WILL use a laptop despite the “danger.”

If the mixer thing can operate without power or water pressure, then sign me up.

http://en.wikipedia.org/wiki/Thermostatic_mixing_valve

Sounds solid state using the same wax style thermostat as your automotive idea. I am making a water heater as well so this is good info for if I plumb it into the hot water supply.

Good old mechanical adjustable T-stat based technology, so no electricity is no problem. I bet they need a minimum pressure, though. Not sure if gravity feed is enough.

Here is a place that sells them (no affiliation, but I have bought from them) http://www.pexuniverse.com/honeywell-mixing-valves
They also have all the documentation in PDF for most things so you can read up from there. Great resource even if you don't buy anything.

Cheap insurance that should be installed on any wood-fired hot water system IMO. or solar. It adapts for the wildly varying tank temperatures so you don't have to.

Good point about overheating with solar. I looked around and found this British company. They say that they can work on gravity feed.

It had the longest link address I've ever seen which made this page 3 feet wide on my screen. Very awkward to read.

One thing these valves don't address is the problem of lag time for a large vessel of water. But being able to heat the tank to say
180F and then mix with room temperature water would effectively provide about 11 gallons at a comfortable temperature from a 5 gallon hot tank.

Dale Hodgins wrote: But being able to heat the tank to say 180F and then mix with room temperature water would effectively provide about 11 gallons at a comfortable temperature from a 5 gallon hot tank.

Yup. That is also how I can get by on a 50 gallon tank when I really should have 80-120.