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hot water

Started by breederman, October 28, 2004, 05:48:46 AM

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breederman

The propane man just filled the tank yesterday and the bill got me to thinking.
   I have an inside wood furnace and wonder if anyone has any ideas on how I could plumb up a coil in or on the plenum to heat water and then dump it in my water heater simply and safely?
    Could I just tee off the hot line,run it through the coil and put it back in the cold side? would I need a circulating pump? They are in the same room/height.
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WH_Conley

    I did that. You won't need a pump if you use it as pre-heater. Cut the input line, run it to your heating coil and back to cold water in on the tank. That way your water heater just has to keep it hot not heat it from cold. If you would put it inside the firebox you get into a whole different ballgame as far as pressure and relief. A lot more complicated.
Bill

chet

I would put a tee in below your relief valve and one behind your tank drain. Then run a line from the drain tee to the heating element then back to the tee under the relief valve. This way the water in the tank will constantly circulate and be heated by way of a thermal siphon.
I am a true TREE HUGGER, if I didnt I would fall out!  chet the RETIRED arborist

beav

   Yes you could. A coil of 1/2 or 5/8 flex copper layed on the plenum plumbed from the drain to the hot out  on your tank will allow you to shut off the propane during heating season. The temperature would be unregulated so a tempering valve might be in order.
   The only problem might be your h/water tank might have to be moved up on a stand to allow thermosiphoning to work. Otherwise a circulating pump with a differential thermostat would be required. For simplicity I'd move the tank up.
   The t/p valve already on your h/w tank will take care of the safety issues. If you do this you will probably want to shut the gas off to the heater and plug the flue cuz the heat will be constantly bled off. In order to use all the hot  water available you may have to enforce mandatory 20 minute showers for all :) ;) :D 8)

SwampDonkey

We tried the hotwater tank hooked to the furnace deal and it didn't last long because of corrosion and lime buildup. We installed an electric and pay $4.95 a month to the power company. The power bill in summer is under $60 and in winter its under $100 per month. The extra power drain is the motor driving the fan on the furnace. Not saying its a bad system for some folks, it'll probably save you a few $$ in the long term if you have a large family using alot of water. But, for me here alone there's no real advantage. Some folks I know turn off the power to the hotwater heater when not needed, then turn it on for a few minutes when needed for bathing.

cheers
"No amount of belief makes something a fact." James Randi

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Woodcarver

We have a hot water coil (actually a V-shaped stainless steel tube) in the firebox of our wood furnace.  It's connected to a tempering (pre-heat) tank.  Cold water supply runs to the tempering tank and then to a propane fired hot water heater that heats the water when we aren't using the furnace.

Circulation to the tempering tank is thermal siphon as Chet described. We used an old hot water heater for the tempering tank and added an expansion tank to deal with the thermal expansion, pressure issue Chet mentioned.

The system works well, but does require mainenance to prevent lime buildup. The tube in the firebox is fitted with tee's with plugs in the ends that I can remove to clean the tube.  I use industrial strength (20%) vinegar to remove lime.  I've been told that the cleaner used to clean pipeline milkers in dairies will also work, but I haven't tried it.
Just an old dog learning new tricks.......Woodcarver

breederman

thanks guys!
   I have the exact tempering tank set up that woodcarver described. Would you plumb it through both tanks as one unit or just the tempering tank? Would I need the expansion tank as both tanks have relief valves?Does my coil need to be lower than where it enters the tank?
    Thanks in advance.
Together we got this !

Buzz-sawyer

    HEAR THAT BLADE SING!

Lenny_M

 Hi all
 Got the parts to the domestic hot water from the boiler but havn`t found the time to put it in.
 Plan on using a heat eachanger like you would find on a hydrualic power unit (20"long X 3" Dia) In line between the wood boiler and the first baseboard on the second floor.
Temp runs around 180-190 deg (unless kids feed the &%** out of the stove.
  Domestic water would feed through this from the cold water feed looped through the heat exchanger back to the top of the water heater. May have to raise the water heater for the thermal circleation
  180-190  deg is a bit hot for demostic hot water so a mixing valve is needed  to regulate the temp to the delivery side .
   NOTE  whenever tying into the system MAKE SURE YOU`RE PROTECTED WITH THE PROPER  RELEIF VALVES
                               Lenny
                All around maintence (millwright) type guy.

 EDK  If you need a hand or a bit of guidance with your system Let me know.  I`m about 4 miles from you.
  We may have met somewhere? Are you in the centr of town? Carl Y ring a bell?

breederman

Still working this out in my head.Is my goal to get the inlet higer than my coil or the outlet at the bottom of the tank higher in order to get this thing to circulate with no pump? :-/
Together we got this !

beav

   Craig- The thermosiphon is actually a misnomer for gravity siphon. Hot water weighs less than cold water.The higher you can get the h/w tank the more efficient it will be. I installed my h/w storage tanks right up to the ceiling leaving just enough room for plumbing it.
   The process works as long as the hot water can rise.If the center of the tank is above the coil it will still work, but it will reverse flow when the furnace is out. A check valve will prevent this but will also slow the flow.
   hth. Jay.
   Keep asking questions ??? ;D

breederman

   Thanks beav! I can move my tempering tank up easy enough.It wouldn't be to hard to raise the heater up as it is  a forced vent through the wall, but I will have to check on the allowable clearance from the top of the unit.
   I think I can place my coil inside the furnace cabinet,that would get it down close to floor level.Am I thinking right? ???
Together we got this !

beav

   Craig- Yeah, I think you've got the idea. I'm starting to think maybe your tempering tank would handle the DHW duties. How big is it? Why not totally bypass the  propane unit when the furnace is running and draw off it?
   I think that is what woodcarver has, but his is in the DHW coil built into his boiler
    HTH. keep asking.. :D ???.

Woodcarver

The two heaters I have are actually connected in series.  The cold water supply runs to the inlet on the tempering tank.  The outlet on the tempering tank runs to the inlet on the propane water heater. We draw our hot water from the propane heater

In the summer, when we're not using the wood furnace, the water sitting in the tempering tank will warm to room termperature (depending on the amount of water we're drawing) reducing the amount of propane needed to heat it.

I have several in-laws who have similar setups.  They use uninsulated water tanks for their tempering tanks.  They lose some heat when using the wood furnace, but gain more tempering in the summer months. Which is best, insulated or uninsuIated, I don't know.

My tempering tank isn't elevated.  The coil in the furnace is about at the mid-point of the tempering tank. Probably would be better if the tempering tank were elevated, but it seems to work OK.


Just an old dog learning new tricks.......Woodcarver

breederman

Would a copper coil of 3/8" work better than 1/2"? Less water to surface area?Any guess as to how long a coil I should use? I'm thinking to make a coil of soft copper in  a frame and put it between the cabinet and the fire box.The out side of the cabinet gets hot with a big fire.We have so much radiant heat that I have a fan on a thermostat in the door to the utility room that blows heat out into the basement.
  My temp tank set up is the same as woodcarvers I think I'll raise it up 2 feet to the ceiling.It is 5feet tall 40 gal?
   One other concern I thought of last night--- the house is plumbed with cpvc,it has worked fine but if the water is too hot I wonder about more expansion of the pipes and then leaks at conections.
   Thanks for your help! All too soon fire will have to be 24-7 snow showers in the forecast for the end of the week. :(
Together we got this !

Jeff

breeder man you have the ability to delete your extra post(s). :)
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

IndyIan

Breederman,
Just be careful what you're doing, a coil on the outside of chimney pulls heat out of the chimney and you can get alot more creosote build up than you normally would.  Just make sure you check once and a while so you don't get a chimney fire.   :(
Ian

beav

   I think 1/2 copper would be better to allow more flow. I like the idea with the frame. Will it be flat or vertical? the vert. would have to be set up like esses but the horiz coil could be a coil with the top pulled up a bit- you kind of have to let the hot water make its way up the coil as it heats.How far away is the tank from the furnace?
   Not too sure about the cpvc... The system pressure is limited by the T/P valve on the hot water tank (if you bypass the prop.heater you'll have to put a T/P valve on your tempering tank). I would think that a tempering(or mixing) valve would take care of temperature issues,and pressure would be similar...
   Yep, the woodstove's crankin'- might snow here tonight :(

breederman

It's going to be vertical in order to get it down on the side closer to the floor.
    About 15 feet  to the tank. The reason I was wondering about the smaller pipe for the coil was maybe it would heat faster/higher in the coil and that would make for better circulation?
Together we got this !

Buzz-sawyer

I have a question for some of you hvac experts.
Why couldnt a large high capacity/high efficiency water heater be used with a circulation pump as a boiler?
    HEAR THAT BLADE SING!

Mark M

Buzz

I'm not an expert (but I saw one on TV), this is sometimes done especially in radiant heat systems where lower temperatures are needed. Some states have law forbidding this practice but I don't know why.


beav

   Both sizes would work,one probably better,who knows which ? 3/8 might work better in a vert. orientation.I kinda think bigger is better cuz when your furnace is really cranking you want it to move enough water to carry the heat off.I used 1/2 cuz I got a bunch real cheap in a yard sale. I wished I'd tried 5/8. But my case is different- I wrapped the outside of a beehive type stove and it is a seperate zone to my solar hot water storage tanks.
   As for how much tubing, I would say as much as you can get in there.  :)

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