SF-250 Hot Water Coil

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Cap
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Hand Fed Coal Stove: Harman SF 250, domestic hot water loop, heat accumulator
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Post Mon. Oct. 02, 2006 7:06 pm

Eric--
Too early to tell. The temp cracked 200F one time but that is the temp of the incoming water to the top of the tank. Obviously the bottom of the tank is closer to the well water temps.

My wife is complaining about all of the *free hot water* cause it is hotter than what she is use to seeing. I think once I start burning coal on a continuous basis, the temps of the water will remain more constant. Hopefully I can maintain 150F or thereabouts. I have 40% of my firebox reduced so I really don't burn as hot as I could. A 2nd tank would be a great idea, ( maybe a used LG-45 liquid nitrogen vacumm jacketed ss container? ) But one of those may be hard to come by. But seriously, I did think bout it, but I don't want to buy a tank. Really no need for it. Once the water at the bottom of the 80 gal tank becomes warm, the natural migration should slow down and I'll probably create steam at the top of the loop thus the reason I installed the bleeder valve.

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endinmaine
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Post Tue. Oct. 03, 2006 3:15 pm

Cap,

Great ,, please us all updated with your findings. I will look forward to them.

Eric

tiogacounty
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Post Tue. Oct. 03, 2006 8:47 pm

cant you cut the outershell of your hot water heater and install an aquastat made to fit. thats how my hot water stayed controlable with my outdoor woodburner

wenchris
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Post Fri. Oct. 06, 2006 2:06 pm

Just ordered a Hilkoil hot water coil. It will be installed in a Harman Mag Stoker. I will be using a tempering tank with a cirulator as the level of the tank is below (In basement and stove is on 1st floor) and about 25 ft from the stove. Is one relief valve at the tank enough, or should one be put up near the stove? Trying to keep this as least noticable as possible.(Stove is in living rm.) Thanks Jimmy

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Post Thu. Nov. 02, 2006 4:41 pm

Finally got my coil in the stove today, what a job that was!

I thought that I made it small enough to manuver into place, while keeping it big to gain the most heat I could. I barely got it in place, had to take the stoker unit off the back of the stove, and it was still a bear.

Word to the wise, make your coil just a wee bit smaller than you think you have to...

What made mine harder was that I put the feed lines in one corner straight through the floor of the stove. The floor on mine is the only single wall steel, the rest is two layers for an air jacket for the blower to ram air through.

I didn't hook up the plumbing yet, will probibly do that this weekend.

*** Cap,

I got two copper couplings that fit the 3/4" OD to the 3/4/" copper nice and tight. I was told that I have to braze the connections and got the special bar & flux for it. Do you think map gas will do it? I couldn't find compression fittings to do the job, if you happen to have two, I'll gladly buy them from you.
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Coil in coal stove.jpg

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Cap
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Hand Fed Coal Stove: Harman SF 250, domestic hot water loop, heat accumulator
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Post Thu. Nov. 02, 2006 4:50 pm

Try brazing it if you are sure the connections are correct. Direct your heat on the copper the entire time and allow the heat to migrate to the ss. If you *burn* the ss, stop, cool with cold water, clean with emery and retry. Sweating copper to ss is a challenge but so far you seem to be made of the *right stuff*! You will need silver braze at least 35% with white or brown flux.

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Cap
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Hand Fed Coal Stove: Harman SF 250, domestic hot water loop, heat accumulator
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Location: Lehigh Twp, PA
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Post Thu. Nov. 02, 2006 4:55 pm

The coil I installed is working just a little too *good*. A modification is in order. I am blowing the main relief valve on the tank cause the water temps are reaching nearly 200 F. So I have been isolating the coil from ime to time. I have a trash can under the relief and I can easily dump 15 gals overnite. I plan on repiping it this w/e moving the relief valve away from the flow of the hot water. I knew this was a mistake. :x

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LsFarm
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Post Thu. Nov. 02, 2006 9:07 pm

Mark, Eric, George, and anyone else. Please consider using a tempering valve at the exit from your normal hot water heater, just prior to getting to the supply to the rest of the house.

Most domestic hot water is around 120*. any hotter and you risk getting scalded or a burn. If you use up the cooler 120* water in an average 40 gallon hot water heater, and then the 200* water gets into the supply you can have some painful consequences.

If you have kids taking showers this could be serious.

A tempering valve is not real expensive, around $50 if you shop around. and also not difficult to hook up. It adds water from the cold supply line into the hot water to control the temperature, it is manually set with a simple knob.

If I was at home I'd take a photo and post it, but I'm in Houston tonight. Maybe this weekend I'll get a photo and some links to suppliers of tempering valves.

Mark and Eric, I think you may have too much of a good thing: too much coil area for the amount of heated water you will be using. It may be necessary to hook up a length of baseboard heat or radiators to the system to drain away some BTU's.

Greg L

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LsFarm
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Post Sun. Nov. 05, 2006 12:16 am

I was playing with my laser thermometer today, and I checked mt hot water temperature at the tap.

With my boiler pre-heating my water and then going through a tempering valve I have water that I find uncomfortably hot if not mixed with a little cold water. I measured the temperature, and came up with 110*, which surprised me, I would have guessed 125* or so.

If I were to take a shower under pure undiluted hot water I would have some minor 1st degree burns. It is that hot to me.

I also checked everywhere I could to find prices on tempering valves, I swear I paid only ~$60 for mine. But he lowest I could find was $102.

So the valve costs more than I remembered, but it takes much cooler water to be uncomfortable or dangerous than I thought.

Greg L

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endinmaine
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Post Sun. Nov. 05, 2006 9:17 am

Greg,
Great suggestion ,, I was thinking about installing one also but did not know what it was called. One my new home is built and I installed my Mark III with the SS water loop I will add this and take pictures.
Do you have an idea of how big the storage tank should be ,, 80 , 100 gallons or larger ?
Years ago my father designed a system using a 30 gallons tank with a very small wood stove that was used only to take the chill off the kitchen for 2-3 and the whole 30 gallons was piping hot,, way too hot to use without mixing plenty of cold water. My concern is that my Mark III will over power an 80 or 100 gallons storage tank and constantly blow off extra water. Some one's suggestion to add a radiant coil to use the excess hot water was also good.

Eric

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Matthaus
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Post Sun. Nov. 05, 2006 9:36 am

Pex Supply is a good source for this kind of stuff. They have tempering valves (120 to 160 degree F) for as low as $38.

http://pexsupply.com/product_dtl.asp?pID=3665&bra ... ts&cID=329

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LsFarm
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Post Sun. Nov. 05, 2006 11:13 am

Thanks Matt, I was sure the valves could be bought reasonable.

Eric, personally I wouldn't buy a storage tank, I'd resurect a discarded hot water heater and use the tank. If one 40 gal isn't enough, I'd add a second in series.

Greg L

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endinmaine
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Post Sun. Nov. 05, 2006 11:36 am

Matt , thanks for the link for the mixing valve.

Greg,
I'm still concerned that a 40 gallon old hot water tank would be overwhelmed with the heat output of my Mark III as my experience above with my father's setup. If there was a constant drawing of water then that would keep the build up in check but when no hot water is being used the larger stove would quickly heat the tank to 200* or more blowing the safety valve. A 2nd tank would be an option.

Eric

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LsFarm
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Post Sun. Nov. 05, 2006 4:19 pm

Eric, how about putting a length of baseboard finned tubing in the loop, this would convert some of the hot water to heat.

Greg L

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Post Wed. Nov. 15, 2006 11:34 am

Does the coil in the stove have to be mounted directly above the fire? or can it be mounted on the inside side of the stove next to the fire? I don;t want to get it too hot, there is only 2 of us and no one is usually home all day...

Thinking about doint this when we move, since the stove will be in basement. I need to replace the hot water tank and will use the existing one as a tempering tank. If using 2 tanks? How does the 2nd one get the hot water circulating without opening a valve? anyone have a drawing of a setup for 2 tanks?

What is a good pump for this application? Thanks!

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