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Hot water pre-heater tanks next to wood stove?


Billy_Bob
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I've been reading these forums for a few days and thought what a great place to ask certain tricky code questions BEFORE construction!

Is this ok? (I'm not a home inspector)

Anyway I want to install two 50 gallon water heater tanks next to my woodstove to pre-heat the water before it goes to my electric hot water heater. The chlorinated city water entering my home is 40 degrees F. and the area next to my wood stove is typically around 110 degrees F. when I am burning wood.

Note: Water boils at 212 degrees F., so no danger of steam being created with this setup.

I've set up temporary tanks to see if this works, and it works so good, I don't even need to have my electric hot water heater on! The water is hot enough for a shower.

Anyway now I want to install these two 50 gallon water tanks "to code". But is there a code for something like this? (This is in Oregon BTW)

I'm thinking that installing them like a water heater would do the trick? (Drip pans with drain, T&P valve, and earthquake straps to hold tanks in place.)

However this is in the living room, so it is visible by occupants daily. Any leaks would be seen right away. So I don't know if a drip pan would be necessary in this situation?

I prefer to use galvanized piping for the connections to these tanks as I need all sorts of valves to fill and drain them (Need ridged pipes to support these "ball valves"). So there are no flexible connections as would be with a regular water heater.

I don't know if it is a requirement to have flexible lines connected to a water heater? Or to these tanks?

Also these tanks are from old water heaters (insulation, heating elements, and dip tubes removed). The cold goes in the bottom and warm out the top. I suppose a check valve would be required where the cold goes in the bottom so water would not flow back into the city water system if there was a loss of pressure.

Anyway what codes would apply for something like this?

If you were inspecting a home with tanks like these, what would you want to see? What would be OK?

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Hi,

Yes, it's ok to ask your question here.

What you're essentially doing is emulating an indirect water heater system using tempering tanks. You could have actually purchased tanks for that purpose instead of tearing up old water heaters to do it. I looks like you've already figured out the other requirements, so I think that the only question you really need answered is the one about whether you need flexible connectors at the top of the tank, since Oregon is in seismic zone 3, no? Check with you local code guy and make sure that you install T & P valves on those tanks regardless of the fact they can't boil.

Jim, Chris, or one of the other Oregon folks will need to help you with the codes 'cuz I don't know which ones they're using down there.

ONE TEAM - ONE FIGHT!!!

Mike

P.S.

Did you know that there are wood stoves designed specifically to work as water heaters? All you need in addition to the stove is a circulator. You plumb them into the regular water heater tank. They have a radiator in the firebox that's heated up by the fire and then that water is circulated into the water heater.

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Originally posted by hausdok

...Did you know that there are wood stoves designed specifically to work as water heaters?

Yes. These are very expensive, so not an option for me.

Also people have designed pipes which go directly into a woodstove or pipes which wrap around the chimney. In both cases I have read of problems with overheating (steam), and with the chimney heat exchanger idea, this cools the chimney and they have trouble with draft/creosote buildup.

I want to stay away from steam since I've read just enough about this to know how dangerous it can be! (Boilers blowing up and launching through the roof and into a neighbor's house, etc.)

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I would also put expansion tanks on there. Thats a fair volume of water and as it heats up is volume will increase quite a bit. If you have a check valve on your city water supply you would absolutely need expansion tanks and if you don't it's a good idea anyway.

Steam isn't necessarily a problem by itself. It will become a problem since, contrary to your statement, water doesn't boil at 212 degrees when it is under pressure... Under city pressure you could easily achieve 240 degrees without boiling, then the instant that pressure is dropped sufficiently to allow boiling, the entire mass of water flashes to steam instantly. Then your having a bad day.

Another issue is temperature control. It's kind of hard to turn down a fire when your water is getting hot enough to make the steam problem a real issue. With the T&P valve in place and all you have protection but that is only after a problem develops. There are some fancy controllers out there that you could use with solenoid valves to basically dump water to cool a runaway situation but now your getting very complex and expensive.

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Unless you have physically piped the water supply to the bottom of the tanks, I would put the dip tube back in.

Make sure that the tpr's are in place and operational. This will help with temperature control in case it gets too hot. Another option would be to place them at a level higher than the heat source and take advantage of thermo siphoning using copper tubing. Google "thermo siphoning" for more info.

Place a pan under them, move the assembly to another area of the home if you are worried about looks. In reality, this isn't going to be pretty anyway.

BTW, I did this several years ago by placing an old 20gal. electric heater tank (with the element removed) on top of my wood burning furnace. The furnace was heavily jacketed so it was actually like placing it on top of the plenum instead of the burner wall, which protected it from too much heat. It worked great as I would have to use at least 20 gallons of hot water before I would introduce cold water into my gas water heater.

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I do have the tanks painted flat black as I read that this would absorb the heat better.

Also I have a pressure gauge on the tanks and it reads the same transitioning from cold to warm. So there is no check valve in my water piping from the city. Water expands back out into the city pipes.

BTW I looked through the Oregon codes and did not see anywhere that flexible lines are required for water heaters???

Codes aside, I want a safe and durable installation. Is it better to have flexible lines installed to a water heater for an earthquake?

Is it possible that with galvanized lines connected to a water heater that these could break and flood the house? And that with flexible lines, these would have a bit of give and not break?

(I will also install earthquake strapping per code.)

Or is it just that flexible lines are intended for easier installation?

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  • 1 year later...

Billy,

I've been looking all over the internet---trying to find some information about putting a hot water tank NEAR a wood stove. I'm not much interested in CONNECTING a tank to the stove (way too hazardous for my taste!) Your post, is (so far) the only info I've found about the tank NEAR a wood stove idea.

My situation is "slightly" different than yours. I'm presently using a 20 gallon gas hot water heater--- that small because it is running on a VERY limited supply of free natural gas. I can only run that heater on the tiniest of flames, but we manage to squeak out two showers a day---and the heater just barely recovers from that! So... I've been trying to come up with a pre-heater tank(s) for this little heater.

I have a propane refrigerator which puts out a good bit of heat from the flue in the back. I experimented by propping up a 4 gallon pot of cold water over that flue---and it got up to 120 degrees ---AND held at that temperature overnight.

SO... I'm going to get a 6 gallon electric water and install it in the small cabinet over the fridge. (I'm off-grid, so I cannot just plug in that tank!) I will aim the flue at the bared bottom of that tank--leaving the insulation on the rest of the tank. I'm quite certain that preheating will help our situation year round.

THEN... I got to thinking about adding yet ANOTHER tank... a 40 or 50 gallon tank NEAR the wood stove---as either a pre-heater for the refrigerator tank (in the summer) and then just use a 3-way ball valve to let that wood stove tank be the main source of hot water during the winter--and then we might have enough hot water to consider ourselves living almost like normal folks!

What a CONTRAPTION! So far, I've drawn a zillion diagrams---and always trying to design the valving so that no possible combination of valve settings would result in a "closed" system---with heated water having no where to expand into.

My cold water supply is a 1200 gallon tank up on the hill that gravity-feeds down to the house. Any expansion in my hot water system would easily push that water uphill.

HOW CLOSE IS YOUR hot water tank to the wood stove? Is it right up against it? A few inches? Please give me any additional details on what you have noticed and learned thus far.

I'm contemplating using a new electric hot water tank for putting near the wood stove---and stripping away ONLY the portion of the insulation and jacket that faces the stove. I figure the remaining insulation would help CONSERVE whatever heat the stove puts into the tank.

I'm a firm believer in Temperature Pressure Relief valves and will also install a small bladder-type expansion tank in the cold water line leading to the tank which will be near the wood stove. Safety first.

All if this is SO MUCH more interesting than just installing a great big propane water heater---and then sending a huge check to Amerigas each month. My philosophy is to spend ANY amount of money investing in a situation which will allow me to live without paying monthly bills. I invested in photovoltaic panels and batteries to avoid an electric bill. But I do use a modest amount of propane for my cook stove and refrigerator. I have lived with a wood cook stove, but they are a bit of a hassle and not pleasant in the summer.

PLEASE tell me any tidbits you have learned about this project. Thanks.

Gene

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Hi,

Yes, it's ok to ask your question here.

What you're essentially doing is emulating an indirect water heater system using tempering tanks. You could have actually purchased tanks for that purpose instead of tearing up old water heaters to do it. I looks like you've already figured out the other requirements, so I think that the only question you really need answered is the one about whether you need flexible connectors at the top of the tank, since Oregon is in seismic zone 3, no? Check with you local code guy and make sure that you install T & P valves on those tanks regardless of the fact they can't boil.

Jim, Chris, or one of the other Oregon folks will need to help you with the codes 'cuz I don't know which ones they're using down there.

ONE TEAM - ONE FIGHT!!!

Mike

P.S.

Did you know that there are wood stoves designed specifically to work as water heaters? All you need in addition to the stove is a circulator. You plumb them into the regular water heater tank. They have a radiator in the firebox that's heated up by the fire and then that water is circulated into the water heater.

I inspected a home last month that had the stove setup and used to supplement the boiler heat.

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You need to look into a solar thermosyphon(sp?) system.

Tom

I've been a bit discouraged into looking at such a system---in the winter months, my direct sunshine is limited to between the hours of 10:30AM and 1:30PM. (The joys of having a house nestled between two steep hills...) I have a sizable investment in photovoltaic solar panels---and, while that helps a bit in the winter, I am not getting the full benefit because of early morning and late afternoon shading. They do very fine in the summer though--when the sun is higher in the sky. Perhaps I should sign up for one of those "mountaintop removal" projects they have going elsewhere in the state. (Heaven forbid!!!)

When I first moved out here and was living in a backpacking tent while building a cabin, I rigged up quite a nice outdoor solar shower with a large surplus refrigeration coil, a pull-chain valve, and a huge flat-faced shower head which must have been delivering 10 gallons a minute! [;)]

Basic truth: The worst possible shower--taken outdoors--is light-years ahead of the best shower taken inside a building.

Over the years I have gone through all the phases of looking into just about every possible alternative energy source and have come to the conclusion that I have:

  • too-little stream flow and head in my creek for hydro
  • too fluky wind conditions for a wind turbine
  • and not enough sun to warrant any year-round projects.

Though none of this has stopped me from setting up really small demonstration projects to amuse myself.

Now, I've decided to try to take advantage of using the small bits of energy which are presently escaping untapped---starting with my gas refrigerator. This morning I ordered a six gallon water heater which I will shoehorn into the cabinet above the fridge and use it as a preheater for my basement gas water heater. I'm hoping to hear a progress report from Billy_Bob on his "tank near the wood stove" project and tie that into the system as well. (I tried sending him an email, but that feature was turned off for me--- Hint, hint, moderator!) Oh, I'll probably go ahead anyway with the entire project because:

  • The pencil sketch looks like Rube Goldberg inspired me.
  • The (undeniable) bragging rights.
  • and lastly, the consternation all of this is causing my lovely wife when she hears that she is about to lose a kitchen cabinet and also have to look at a "large, ugly, painted, tank in our smallish living room!"

Life is short; might as well have fun.

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Gene,

I still think the thermosyphon will work, even if only as a preheater. If you can build all that stuff living out of a tent, then you should be able to build a simple thermosyphon, my first thought when I saw the Sunmaxx kit was that I could build one. The basic principles might even allow you to scavenge heat from lots of sources into a single storage unit. BTW, you should be thinking of heat storage as a medium separate from your potable water, once you do that the posibilities are almost limitless.

Tom

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Billy Bob,

I don't know anything about Oregon codes, but I like your idea. Pratically speaking:

Since there will be no direct heat source on your tanks (they will be near the stove, but not touching it), I think drip pans and drains are a good idea, but unnecessary.

That water will never boil and expansion shouldn't be a concern at those volumes and temps.

I don't think you need a check valve either. What would be the harm if heated water from the tank worked its way back into the cold water pipe it just came from? It's not like we're talkin' about boiler water.

If I came across a setup like that during an inspection, I'd smile. All you're really doing is running the cold water feed to your water heater through a conditioned space.

Cheers to you,

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According to the SunMaxx website, their thermosyphon system is "perfect for warmer climates where freezing conditions are not a problem.... Since both components of this system, including the storage, are exterior, it is imperative that you be in a non-freeze climate."

Our winter temperatures here can drop down to as low as -20 degrees. Add in the very short portion of the day in which the sun could shine on our house (and factoring in the 50% of the time the sky is overcast) I'm not about to get into any sort of passive solar water heating device.

I already have a 2-storey solar green house on the south facing wall of the house--with a considerable amount of mass in a masonry wall--and even with that, there are only about two hours a day when it makes any sense to throw open the large doors and and try to get some of that "heat" into the house. The 10-foot tall thermopane glass is most likely a net heat loser---and I already have enough twice-daily chores around the farm to consider adding insulating window shutters/curtains. As is, the lowest temperature ever recorded in that room (which is not heated by the woodstove) was 33 degrees. Considering how much time I already spend keeping ice and snow off of the solar photovoltaic panels, I wouldn't be keen on adding additional square footage in a water heating system which would require similar attention.

f_mrtfam2p2qm_44100a3.jpg

I spent many hours figuring out the position of the roof overhang---and was delighted to find that, after construction, the sun actually strikes most of the back wall in the winter---and hardly shines in in mid-summer. See the big hill behind the house? There is an equally big hill right behind where the photographer was standing---and if it weren't for that hill, I might be a bit more open to another solar project. The picture was taken on a (rare) sunny day. To the right rear of the house you can see an old Zomeworks passive tracker on a pole which is holding eight Arco M-75 panels.

As you can see, there's plenty of wood to heat with---although being late in the season, little of it is in the wood shed! Last week I finished stuffing it with oak and hickory--a feeling which is similar having to money in the bank.


A note: After considerable browsing on this website, it is just becoming clear to me that the main thrust of the site is about house inspections. (Well, duh!) my posts have had nothing to do with house inspections---and I apologize for hanging around trying to soak up some information.

I would add that no one has ever inspected this house----but I built it always thinking that some day someone might! As an owner/builder, I did a lot of book research, and kept my eyes open whenever I had the opportunity to visit with any tradesmen. I live in a part of the country where such attitudes are not the norm. Many people build their own homes, but few look beyond what methods their neighbor has used. As a result, there are a dreadful number of homes which have completely un-vented plumbing systems, inadequate foundations, and roofs which need re-shingling every presidential election. I remember once passing a neighbor's house and watching him beginning to shingle his house; he had started at the ridge and was on the third course down, when I pulled my car over and sat for a while trying to think how I could approach him diplomatically.

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