Wood-Stove Hot-Water system

[Grahamsurette]

Alright I think I've figured it out.... Normal hot water tank, thermo siphon supply into the top of the tank with the return from my floor Y'ed Into it. Return going back to the stove exiting from the drain at the bottom of the hw heater with the suppy to the floor T'ed off somewhere in this area along with the circ pump. If it was designed correct I think it would work well and the suction from the circ would encourage the flow of natural convection. Thoughts?

[organic farmer]

You sir, have built yourself a bomb. You are just one power or pump failure away....

No, not really. I have pressure-relief valves in the loops.

[Mike90250]

... Unfortunately with my woodstove it was not possible for me to design it for thermal-syphoning. I must use a circulator-pump. ......

You sir, have built yourself a bomb. You are just one power or pump failure away. Or some mineral deposit clogging. If you have a fire stoked up in your stove, and loose circulation, it goes boom in 2-30 minutes, depending. You just said in the nuke subs, they naturally circulate slowly, or else they would go boom too.

[LucMan]

Hi there,
I recently built a 28x32 garage with in floor heat. What I'm trying to do is find a hotwater tank with a heat exchanger built in. I've got a wood stove in the building which I plan to rob heat off of and fill my tank via thermosyphoning. The infloor would be a closed and seperate loop from the hotwater tank, only pass thru to be heated. If anyone has any useful info for me it would be greatly appreciated. Thanks Graham.

http://www.htproducts.com/superstor-ultra-waterheater.html

[organic farmer]

Hmmm interesting idea with the horse trough, I will do a little research on that. I would think that if both systems were taking from the same body of water it would mess up my thermosyphoning. The reason I want the stove exchanger system geared up like this is in the event of a power failure the thing would keep heating the tank and worse case the circ pump for the floor loop would stop. Thanks again

I understand.

I was a crewman on various nuc subs for 20+ years, so I have seen thermal-syphoning applications at work. Our nuclear power plants are designed to do it [but they call it 'Natural-Convection']. When everything is working feed pumps are running, and when the feed pumps are shut-down the system still continues to do 'Natural-Convection' [though at a slower speed].

Unfortunately with my woodstove it was not possible for me to design it for thermal-syphoning. I must use a circulator-pump. My in-floor radiant loop is nearly 1000', simply too long, too much resistance to flow for thermal-syphoning to work well in that application.

However my plan for the added Solar-Thermal array, is to design that loop to thermal-syphon [when it's pump is shut-down].

I suspect that during start-up, the flow may need the 'encouragement' of a circulator pump. If that makes sense.

In our home, we have a Thermal-Bank that we circulate the water through. In the example I used of a horse-trough, if you think of it as being a Thermal-Bank, it is storing the heat for when you need it. Then each individual loop, whether it be a loop from a heating device, or a loop through your floor, each loop can be designed independently in terms of trying to get them into doing the whole thermal-syphoning routine.

[Grahamsurette]

Hmmm interesting idea with the horse trough, I will do a little research on that. I would think that if both systems were taking from the same body of water it would mess up my thermosyphoning. The reason I want the stove exchanger system geared up like this is in the event of a power failure the thing would keep heating the tank and worse case the circ pump for the floor loop would stop. Thanks again

[organic farmer]

Hi there,
I recently built a 28x32 garage with in floor heat. What I'm trying to do is find a hotwater tank with a heat exchanger built in. I've got a wood stove in the building which I plan to rob heat off of and fill my tank via thermosyphoning. The infloor would be a closed and seperate loop from the hotwater tank, only pass thru to be heated. If anyone has any useful info for me it would be greatly appreciated. Thanks Graham.

The LPG water-heater I have only has the one tank for water. There is no heat exchanger in it, all water going inside gets mixed with all of the other water in it. This is very common among home/apartment heating and domestic hot-water applications in my area.

My woodstove also heats water, using a 50' coil of 3/4" copper tubing in the secondary combustion chamber of my woodstove.

One in-expensive method of making a heat-exchanger, would be to use a 200-gallon horse trough wrapped with insulation. Drop 50' coils of 3/4" copper tubing in it. Then you would have two separate bodies of water sharing heat with each other. This is what I plan to do when I add an outdoor Solar-Thermal array into my heating system.

[Grahamsurette]

Hotwater storage tank

Hi there,
I recently built a 28x32 garage with in floor heat. What I'm trying to do is find a hotwater tank with a heat exchanger built in. I've got a wood stove in the building which I plan to rob heat off of and fill my tank via thermosyphoning. The infloor would be a closed and seperate loop from the hotwater tank, only pass thru to be heated. If anyone has any useful info for me it would be greatly appreciated. Thanks Graham.

[Mike90250]

Wood pellet stoves often have a hidden cost - the 300w of 120VAC needed to run the auger, fan and ignition circuits.

[organic farmer]

Our woodstove heats water. The heated water circulates through a Thermal-bank under the floor. That also circulates through our radiant heated floor.

It allows me to capture more of the heat produced, to store that heat, and to transfer that heat to the rest of the house.



I hope to eventually add a Solar-thermal array, and then to begin circulating from it, to our thermal-bank as well.

[derekza1979]

I'll have to suggest something to my friend who has a cabin and heats with a wood stove, it sure would save a few hundred over the winter months in electricity!

Sounds quite extraordinary. Speaking about wood pellet boilers is the effect the same?
I am asking you because wood pellets are becoming extreemely popular judging by offers http://ukrfuel.com/wood-pellets-b327.html

[LucMan]

Keeping the flue temp over 275 F minimizes condensation & creosote formation.

[J.P.M.]

What temperature is the dew point.

Kind of oversimplifying and not absolutely correct, but the dew point temp. for the water vapor in the flue gas mixture (water vapor being one of the products of combustion) is that temp. of the gas mixture where the water vapor in that mixture just begins to condense. Not usually a good thing unless accommodated for in the design somehow. The H2O can then combine with other gas products and depending on the fuel, air/fuel ratios, and other variables, produce corrosive or generally bad stuff. The dew point temp. is a variable number, depending on the many of the same and more variables mentioned above.

[Johann]

One comment about scavenging waste flue gas heat -- beware of flue gas condensation. Burning wood produces large amounts of moisture (hydrocarbons + O2 => CO2 + H2O ...) and you don't want to cool the flue gas below the dew point IN the flue gas stream. That's why super-efficient heaters and the like require double-walled flue pipes -- to prevent additional cooling and condensation.

What temperature is the dew point.

[Paul Deel]

Greenhouse is right to be wary of overcooling the flue gases. Only 60' of 3/8 tubing on the outside of a 6" flue pipe on an air tight stove should be pretty safe though. One suggestion for greater efficiency would be to break up the laminar flow up the flue pipe with the use of a diverter inside the flue pipe like those used in gas water heaters. Laminar flow up the flue allows the hottest gases to flow straight up the middle of the pipe while the cooler air next to the pipe wall will tend to insulate the wall from the hotter interior gasses. Down side of course would be cleaning the thing.
I like the use of a "hot water dip tube" in the cold water supply to the water heater. It allows maximum hot water stacking in the water heater.
As a young plumber many, many years ago we heated water with 1" Type K copper coils and a gas or coal fire under it. Water circulated by gravity into the hot water storage tank near the basement ceiling. From there the hot water rose to the attic and circulated by gravity to every fixture and back to the tank. Instant hot water at every faucet and no pumps.