heating hot water with a wood stove.

[muddstopper]

We keep a 40qt stock pot filled with water on the wood stove during the winter. It is set on top of some old fire brick so it isnt direct in contact with the stoves surface. I have check the water temp several times just to see how hot the water gets and it usually around 150degrees, but will jump up to about 180degrees if the stove is really stoked up. This got me to thinking about trying to capture the hot water and route it thru my hotwater heater. I have looked at several of the hotwater kits for wood stoves, but dont really like the design, or cost. I am thinking if I can heat a large sealed tank on the stove, i could just plumb my water supply to the tank and then to my current hot water heater. This should supplement my hot water supply and reduce my electric bill some during the winter months. Of course i dont want 150 or 180 degree water comeing out of my shower head, but since raising the pot just a few inches off the heater surface seems to greatly reduce the water temp, I can probably experiment raising the tank to a height that would reduce my chances of getting scalded. I have a small 6 or 7 gal water heater that is just setting around, which is what I am considering setting above the stove and connecting to my water supply and water heater. Give me a few opinions on if this should or should not  work. Should I add a recirculating pump between the two water heaters, or just let the incoming water flow thru the wood heated tank and on to the bigger hotwater heater whenever we use hot water. I dont expect the saving to be huge, but investment cost is also pretty low, just needing a few feet of pipe to connect it all.

[WH_Conley]

I have been thinking along those lines too. My wood stove is in the basement, so is the hot water heater. The water line comes through the wall next to the hot water heater and splits off to the rest of the house. I have thought of setting an old water heater tank, without outer skin or insulation next to the stove. Route the incoming water to it first. A "tempering tank", I think is the proper term. Another idea is simply to take coiled copper line and hang it over top the wood stove. Warm it up some before it hits the water heater. I agree, the savings wouldn't be huge. Every little bit of propane saved would help.

[r.man]

A lot of your decisions are going to be based on budget and space so it would help if we knew how much of each you had. My fathers hunting camp had a very basic black iron pipe routed through a barrel stove, and many commercial stove had fittings or holes for this type of thing, that was connected to the top and middle of a 45 gal open steel drum filled with water. This was the hot water supply for the camp. WH, if you had an open barrel hooked this way you could pipe a circulation pump from the barrel to a sidearm heater on your water tank and then back to the barrel. A second thermostat in your hw heater could turn on the circulation pump. As long as the barrel is kept reasonably full the heat bleeds into the basement slowly moderating the temperature and since it is open to the atmosphere there is no steam explosion danger. You could probably run the water directly from the stove loop to the sidearm and then back to the barrel but you would not have any control over the hw temp. I expect a loop or run directly on top of the stove would work well enough for this. This idea would also allow you to run a hot water coil in a furnace plenum to move heat to other places or to heat an in floor system.

[beenthere]

I have a stainless steel 30 gal pre-hot water heater that has a coil inside it circulating boiler water by convection that works very well for me. And in the summer, the cold well water enters this 30 gal tank first so it gets some warming before it goes to the domestic hot water heater (which keeps it up to set temp with LP gas).  The wood fired boiler is to the left of the ss tank.



 

[JuniperBoss]

I've always loved the thought of the wood stove being like the sole thing that powers a home. You can make it create electricity (by steam), heat, and hot water. It can cook food too  :laugh:.
The best thing is it doesn't cost hardly anything to run a wood stove! That is especially if you cut wood yourself. That's self-sufficiency in style 8).

[Ivan49]

A friend of my uses his stove in the basement to heat his hot water. He  has a walkout basement and his water heater and furnace ar in the corner in a separte room. He took the inlet line to his water heater and ran it to his wood stove and made a set of coils on the back to preheat the water. He put a plate over these coils to help hold the heat around the coils. He first tried the coils on top of the stove but the water got to hot and he had no water regulate the temp. He said it put out all the water he needs.

[r.man]

You can preheat the inlet water to save money and if you only ever used small amounts of hot water at a time the savings would be substantial. If however you are like most people and you use a lot of hot water at one time you need to circulate your heated water through the hot water heater some way. If it is unregulated you will either have to keep the primary heat on to supplement the wood heated water or you may have hot water that is too hot at times. Most people I know with sidearms and OWBs have water that is too hot unless they use a separate pump and thermostat for the hot water. The cheapest way is to pipe to the sidearm and then to the plenum coil. People who pipe to the plenum coil first complain of a lack or hot water volume.

[Ianab]

or you may have hot water that is too hot at times

You can get a mixer valve that you connect to the hot water tank outlet. It will automatically mix in some cold water if needed as you draw it off, to keep the hot supply at a safe and sensible number. Gets around the boiling tap water issue.

Ian

[SwampDonkey]

Years ago my grandmother heated the water with an attached copper tank that came with the stove. Then they heated the water by hooking up to a vertical water tank which they used for years. It was in a small closet behind the stove. Always had hot water. But up here electric is cheap compared to some of you guys so people just use an electric hot water tank now-a-days. My electric bill is most times less than $100, but the heater is also looked after by the power company.

[r.man]

Swamp could you figure out the real price of a kwh for me. Take your hydro bill, taxes, delivery fee etc and divide it by the number of kwhs used. I'm interested in how much it differs from Ontario. I also have a small charge on my bill that is called a " debt reduction charge". That one ticks people off. The public utility built up a debt in the past so they are reducing it with a charge to present customers who may not have been customers when the debt was incurred. They should have hidden that one.

[giant splinter]

looks like some great ideas for hot water on a day when the power is out, it rarely happens in my area that the power would be off for more than a few hours so I never think about my electric water heater or well pump being out of juice but I can and will happen to everyone.
My backup water supply and shower is a deep fried turkey fryer (never seen a turkey) that I set up for a wall tent to use on fly fishing trips.
This rig is comprised of a large turkey cooker of the outdoor propane type, a heavy thermometer, a cheap 12 volt marine water pump with an old lawnmower battery, a metal stake that holds the pipe riser supporting one conventional hose bib, two separate shower heads with shutoff valves
one is a ball washer about three feet off the grate and the other is a 6.5 foot tall conventional shower head. This rig is a easy to heat and use portable shower and grandkids think its fun to use in the summer when they have been crawling around in the sandbox all day with their Tonka earthmoving projects.

[SwampDonkey]

In Dec was 580 KWh @ 9.85 ¢/KWh  $57.13

plus    service       $21.63
       water heater  $6.00
taxes                   $11.00

[bandmiller2]

There are many ways to heat your domestic hotwater.Myself I have an outside furnace assisted hot water system.I have an Everhot heat exchanger,my hot water from the outside furnace goes through the everhot first where it heats the clod water headed for the electric water heater.Basically in the winter it preheats the water and the waterheater just maintains the hot water .Summer switchover is seamless the cold water feeds through the everhot to the water heater.I tried just the everhot unit but not quite enough hot water, read quick shower. Frank C.

[muddstopper]

I took a good look at my small electric water heater I had planned on placing on top of the stove. It is glass lined. I read somewhere that the glass lining was only good up to 250degrees. While the water in the tank would probably never get that hot, the top of my stove will. For this reason I have decided not to use the water heater on the stove. The tank also has one inlet at the bottom of the tank that has some sort of plastic insert in it. The stove heat might cause this to melt. Anyways, I am now looking for some sort of small metal tank I can use. I thought about welding up a metal box to just fit the stove top, but steel rust and stainless is expensive. My next ideal is to just get some copper pipe and make a coil, stick it in a upside down metal 5gal bucket and set it on top of the stove.

[r.man]

Mudstopper I would strongly advise against using any kind of closed system unless you have  a reasonably sized reservoir, a circulation pump and a pressure relief built in. This type of system would also be dangerous in a power outage that stopped the pump because of steam and pressure build up. 

[beenthere]

When the electricity goes off, my damper automatically defaults to 'closed'. Any coasting of a fire in the closed system that causes 'steam' is relieved by the relief valve.  A relief valve is standard procedure.
So don't see a danger to the closed system, if there is one.

[muddstopper]

Mudstopper I would strongly advise against using any kind of closed system unless you have  a reasonably sized reservoir, a circulation pump and a pressure relief built in. This type of system would also be dangerous in a power outage that stopped the pump because of steam and pressure build up.

The water heater I had planned to use did have the factory popoff valve. I am thinking the valve on my regular water heater should prevent pressure buildup without having to put another valve on whatever I decide to use for a preheater. Someone please correct me if I am wrong!! Right now, I havent been able find anything smaller than about 45gal galvinized tanks. While it might be nice to have 45gal of preheated water, a tank that size is not practical to set on top of my stove. I am thinking 10 or 15 gal. Am also considering the use of a recirculating pump between the water heater and preheater. This might take some tinkering to keep from getting the water to hot, nothing like turning on the shower and getting ran out of the stall with scalding water.

[muddstopper]

http://www.michigan-horse.org/preheater/

[r.man]

As someone else mentioned there is a device called a mixing valve that can be installed on the outgoing hot water pipe to the house. It also has a cold water pipe feeding it so it can mix the right amount of both to keep a maximum temp in the outgoing pipe. In my area these valves run about 80 dollars. I was thinking that an indoor stove would not be dampered down in a power outage and while the pressure relief should protect I would prefer a system that doesn't require one. If space is at a premium an open system is probably not doable without a pump but with a pump you could put a storage barrel in the basement, pump from it to a coil on the stove and then piped to a sidearm, back to the barrel, no pressure, no worry. It might actually move water with convection since I saw a hot water tank a few months ago that was heating a loop of about 50 ft of half inch copper pipe by convection.

[barbender]

Beenthere, where did you get that tank, and how much are they?

[SwampDonkey]

Indoor furnaces have limit controls that under power will open the draft, but if power is lost this will reverse by gravity from the weight of the chain and damper door. I know we are talking about a different heating system, just saying. Mine works with a mercury switch at the thermostat under power. To close the damper when heat is not called for, the circuit is cut. Works like an hour glass, sorta. On the oil, it turns the burner off and on.

[r.man]

Electric thermostatically controlled devices do, but many indoor wood stoves are manual only or are controlled by a bi-metal non electrical control. Twenty years ago I had a stove like that, safety approved that had a design defect that I have often told people to look for. A bi-metal spring was mounted on the side of the stove above the draft door between the firebox and the outer decorative shroud. A knob allowed the operator to set the desired heat level. If it was higher than present a chain attached to the draft door lifted it open. When the stove warmed up the area and the spring because of the draft door being open the bi-metal changed shape causing the draft door to drop. Pretty standard device used on many stoves of all types. Unfortunately mine didn't have a positive stop on the bi-metal movement and if the stove overshot sufficiently the bi-metal would re-open the draft door. Bad, bad stove. I didn't keep that stove and for years have looked at controls like it. All the control needs, and some have it, is a bolt below the spring to act as a stop. Dangerous thing to miss.

[beenthere]

r. man
That sounds like the old Ashley wood stove I had. Never caused a problem, but was something I worried about happening.

barbender
I bought that tank from the company that mfg. the wood boiler, in northern MN (Babbitt, MN).
But a few years after that (mid to late 80's), the business either was bought out and closed or it folded. In the early 90's, I was so impressed with the boiler unit, that I planned to order a spare (didn't expect this one to last another 20+ years  :D ) but couldn't get any response from them. The ss side tank also disappeared with the business, as near as I have been able to find out. It was $285 fob

[Bill_G]

This is my setup with 120 gal tank and pump . I put a relief valve on the high point in the system and one on the tank . Been working great for two years .

  

 

[r.man]

That's a good looking system Bill, have you ever had the stove going during a power outage? I would be concerned about that but I was also wondering if convection would be sufficient to stop it from boiling. Might be that I am just a worrier.