Water Heater Coil

PostBy: Cap On: Fri Dec 22, 2006 11:13 pm


I tried piping my system in the same manner as you did your loop.

I originally piped from the outlet of the well tank directly to the inlet side of the coil, outlet to to the top of the hot water domestic tank. Should work, right? IT DID NOT CIRCULATE while no hot water demand in place.

The only way I could get natural migration in times with no hot water demand, I had to run from the bottom of the hot water tank ( also the inlet to the tank ) up two feet into the stove, out of the stove up 2' and into the top of the hot water tank. This allowed natural migration via heat expansion

This method allows the domestic hot water to be heated continuesly, whether we are puling hot water or not. If I allow the stove to get too hot, I too will heat the water tank in excess of 200F and blow the relief valve. Luckily, with the mild temps, I have been maintaining 150F at the very top of the tank. By the time i shower in the morning, #3, I am running short of heated water. ( My son take 30 min swims in the shower! ) Once the water at the or near the top equalizes with the coil temps, the natural migration slows and stops flowing.

I am still dumbfounded why my original scheme did not work. I even had a shutoff valve in the standard cold water line at the inlet of the domestic water tank installed outside of the well water inlet.. In my mind, there is no reason why the first scheme did not work.

But if you study the drawing in the Harman manual, it calls for the scheme I have in place now.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: LsFarm On: Fri Dec 22, 2006 11:35 pm

Mark, I think we have some confused comunication. KTM's system is a hot water boiler [pressurized], with a continous loop of water pipe with a circulator pump. The water heated in the boiler goes first through his water/water heat exchanger for the hot water tank, then on to the water/air exchanger which transfers heat into the hot air duct system.

So KTM's system doesn't use any thermo-siphon He was asking about why there was a pressure relief valve in the thermo-siphon system. His system is 'apples' and the thermo-siphon system is 'oranges'.

Confusing I know, but it happens.

KTM's and my domestic hot water systems pipe the cold water going to the water tank through the water/water heat exchanger before it gets to the water tank. In my system, the water is heated to 140* before it enters the tank. I don't know what KTM's tank input temperature is.

With this system, as long as our boiler is producing hot water for the exchanger, the cold replacement water entering the hot water 'heater' is preheated to around 140*. This type of system provides unlimited domestic hot water.

The hot water circulating through the boiler and heat exchangers is separate from the domestic water system. Mine has glycol in it so it won't freeze if I don't fire the boiler during cold weather.

I hope this clears up the confusion. Greg L

Last edited by LsFarm on Fri Dec 22, 2006 11:51 pm, edited 1 time in total.
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: Cap On: Fri Dec 22, 2006 11:49 pm

Okay. Greg.

I do not know much about boilers as i never lived in a home with a boiler. Always had forced hot air/natural gas. I hated it! Of course my parents think I nuts, shoveling coal. But my electric bill not including the $16.50 service charge was under $50 for the month & $75 for coal! Folks at work spend 4x for electric or oil heat.

What is that an image of under your user name? My eyes are blurry up close! I' m over 40 and over the summit, heading back downhill!
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: LsFarm On: Sat Dec 23, 2006 2:44 am

Hi Mark, the image is an aerial photo of most of my farm. It was taken from a hot air balloon several years back.

Greg L

Lets not talk about 'over 40', or 'over 50' either!! I'm both!
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: ktm rider On: Sat Dec 23, 2006 9:28 am


I have forced air heat ( the wife wanted it when we built the house, I'm not that fond of it either) The only thing the boiler does is replace the oil/gas furnace. Otherwise it is the exact same set up as any ordinary forced air system.
I have a big air handler in my basement with a blower in it of course. Then there is a water to air heat exchanger sitting above the blower inside the duct work. My boiler runs hot water through the heat exchanger 24/7. Then when the house thermostat calls for heat it simply turns on the blower inside the air handler and that blows air up through the heat exchanger and then the air goes through my duct work...

You know it is REALLY hard to type explainations of how things work. If you would look at my system for 2 seconds it would be crystal clear.

Not sure if you meant you didn't understand how a coal boiler would work with a hot air system or not. but, if not, there ya go..
ktm rider
Stove/Furnace Make: AHS Multifuel
Stove/Furnace Model: CO 55 with oil backup

PostBy: ktm rider On: Sat Dec 23, 2006 9:34 am

I am clueless when it comes to thermo syphoning. Not even 100% sure what it is really ( I would like to know) but just from reading this, and i may be WAY OFF her but, wouldn't simply putting a temping valve in the loop fix the PRV problem if the PRV is somehow opening because the water temp is getting too high?
then again, why would the PRV open just because the water got to hot?
I have a PRV valve on my boiler and when I over fired it to 240deg :shock: It still didn't pop my PRV because the pressure didn't climb to the set pressure ( 20psi in my case) that would open the PRV.
I'm probably totally off on this one but hey, that is how you learn things, by asking really stupid questions...
ktm rider
Stove/Furnace Make: AHS Multifuel
Stove/Furnace Model: CO 55 with oil backup

PostBy: coaledsweat On: Sat Dec 23, 2006 10:06 am

It is a lot like the draft in your chimney. The warm water rises in the boiler and leaves via pipe to the top of the water tank. The water in the tank is cooler and desends in the tank and out via pipe to boiler bottom where it is heated and rises.
The problem comes in when you use a stove instead of a boiler you expose the coil to a lot more available heat. A boilers water temperature has a control setpoint of say 180F. That is the temperature that the water your are heating is exposed to and the most your hot water would get. In a stove, the coil can be exposed to temperatures of maybe 500F, and if it doesn't move quickly enough through the coil it will flash to steam. To give you an idea what happens then, use this formula 1 cup of water = 16,000 cups of steam. You quickly build enough pressure to pop your saftey valve.

No stupid questions here, we're all scientists. :P
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

PostBy: LsFarm On: Sat Dec 23, 2006 10:47 am

Shawn, coaledsweat described thermosiphon perfectly. Hot water is less dense than cold, so it rises. If the water holding tank is at or above the level of the heated loop the water will rise, and around and around it goes.

As for your question about using a tempering valve. they require pressure and water flow [water being used] to mix the cold water with the hot water, so a standard tempering valve wouldn't work with a thermosiphon system. The flow is pretty slow, and there is not any differential pressure.

Have you ever looked at a Ford Model T? That is the early Ford made up through the mid '20s ?? They did not have a water pump. Water was heated by the engine, rose up to the radiator, was cooled and flowed back out the bottom of radiator to the engine block.

Early 2Cylinder John Deere tractors used the same system. The water hoses and pipes were pretty large, 2.5"-3" if I remember correctly.

This type of thermosiphon loop is as simple as water heating system can get, no pumps, just burn coal in the stove, and the hot water tank gets heated too. The only problem is when the stove runs a long time, and no hot water is used, the tank gets too hot.

A PRV for a hot water tank is not just a PRV. I call it a 'WATTS' valve, but that may not be correct. There is a 'Watts' company so maybe all the PRV valves I've come in contact with were made by this company, rather than being this type of valve?? Don't know.

But anyway, a PRV for a hot water tank, has a temperature sensor, as well as a pop off pressure spring. If you read the metal tag on your hot water heater, you will see that it has a temperature rating as well as a pressure rating.

Sorry for the long post, I should have just telephoned??

Merry Christmas!! Greg L
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: coaledsweat On: Sat Dec 23, 2006 10:50 am

I would say that the WATTS Co. made about 95% of the PRVs I've seen in homes. They have become synonymous at this point.
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

PostBy: ktm rider On: Sat Dec 23, 2006 10:54 am

Clear as mud now. (Just kidding. ) I think I will just stick with the ol' pressurized system.
ktm rider
Stove/Furnace Make: AHS Multifuel
Stove/Furnace Model: CO 55 with oil backup

PostBy: rouxzy On: Sat Dec 23, 2006 10:58 am

MjwoodO, the PRV was opening ever so slightly mainly because there wasn't any demand for hot water yet in the day. Since then it has been fine.

KTM, the reason why my PRV comes into play and yours wouldn't is because in my system the heat is constantly heating the water. The only way to regulate the heating of water is either turn down the stove or use hot water. In your system it is controlled via a thermostat to shut down the heating process when necessary.

Greg, I think I may hook up a leg of baseboard heat because when the temps outside get really cold I feel I will not be able to use all the hot water that is produced. I will use isolation valves so that I can regulate when the water is redirected to the baseboard.

Chad, in my original system the cold water outlet from my tank was about a foot below the cold inlet to the stove. I had hot water with this setup, but now my new system has the cold water outlet from my tank just about level with cold water intlet to the stove and the thermo syphoning works alot more efficiently.
Hand Fed Coal Stove: Harman Mark III
Coal Size/Type: Stove, Nut / Anthracite

PostBy: WNY On: Sat Dec 23, 2006 7:01 pm

From another thread, here is a few pages I found that explains a typcial system...it is PDF format.

Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

PostBy: Charlie Z On: Sun Dec 24, 2006 10:07 am

Hello all, this is my first post. I've been studying hooking up a coil or boiler to my existing system and have only limited 'web-knowledge', which is why I'm a fan of this site. It's terrific.

(I don't have a coal stove and I'm not a HVAC guy, so my comments are worth what you've paid for them.)

Now then, the problem in hooking up a wood/coal/solar heat source is that it is uncontrollable, compared to oil or gas, which can be shut down immediately by stat, etc. With solid fuel, things melt and water boils.

I've read the masonry system report and wonder if a better job can't be done? The swing check valve and TPR are kinda patches to the problem - last-resort type safety devices that are not designed as primary controls.

The thermosyphon system described above is a 'one-pipe' steam system. My aunt still has one of these in her house. Steam rises into the radiators and cools back into water and returns through the same pipe. The oil boiler simply replaced the coal system in 1954 w/o any mods to the system. She could go back to coal anytime and its a marvel of simplicity - no pumps (other than for the burner).

Missing from some proposed thermosyphon systems is the requirement that radiators and expansion tanks have to be above the water line of the boiler. Also, steam systems (best at this no-pump thermosyphon method) require large diameter sending pipes (returns can be small stuff.) My aunt's system is all 2",3" and 4" iron pipe to the rads above.

The masonry system is a hot-water system (not steam) and I don't imagine that it works too well w/o a circulator pump. Pumps keep the water liquid instead of gas. Small-pipe systems came on scene with circulators and importantly, oil and gas burners that can be controlled.

I thought it interesting that the Brits never really got off of open, vented systems and they still use kitchen cookstoves with 'back-boilers', which they connect to CH and DHW. The best description of hooking these up safely for self-control is this .pdf: http://www.solidfuel.co.uk/pdfs/link_up.pdf

They use different terms -- the most unusual was the 'airing closet'; a tempering tank in a second floor linen closet and 'link up' is connecting your stove to CH. Check out the use of the 'neutralizer' in the first section and the control device in the second.

Pretty slick stuff, but you can't use it if you have the closed loop system, like a hot-water/baseboard system most of us have (that aren't forced air).

This is as far as I've gotten to understand all this. What I'd like to find out is what we can do to configure a hot-water system to meet the same designed-in safety and control requirements with our closed systems?

Besto, - Charlie
Charlie Z
Stove/Furnace Make: Coalbrookdale
Stove/Furnace Model: Darby

PostBy: LsFarm On: Sun Dec 24, 2006 10:49 am

Hello Charlie, welcome to the forum.

I had no idea that the brits still use open systems. Maybe this is a carry-over because of the old piping?? I don't know.

You mention reading 'the masonry system report' what is this?? Can you supply a link? Or describe what it is??

These hot water coils are just an attempt to capture and use some of the heat in a hot air stove to reduce the cost of our domestic hot water. I suspect that only 3-5% of the forum members use this system. The plumbing and location of tanks, heaters etc. can make it too complicated and expensive. However, with little if any additional coal use, these members are reducing their cost to heat domestic hot water to near zero during the heating season.

I'm thinking about hooking up a solar panel to a pre-tank for my domestic hot water this spring. This will further reduce my propane use each year.

Take care, Greg L
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: Yanche On: Sun Dec 24, 2006 7:45 pm

Charlie, You make some very good points. Some of the add on features
individuals have added to their room stoves, like domestic hot water and
ducting hot air to existing house heating systems, are short on
engineering, particularly safety engineering. They represent the best
in the application of individual ingenuity and for those that tinker,
they accept the risk of doing so. As you point out solid fuel systems
can not be immediately be shut down and are more difficult to control
the the "modern" fuels. This is largely the reason the "modern" fuel
systems have become so commonplace. Be assured a fully safety code
complainant coal system for residential heating and domestic hot water
can be designed and built with "off the shelf" components. The
difficulty is finding such a skilled designer. It's unlikely you will
find someone in the residential HVAC business. You almost have to
engineer it by yourself. If you are so inclined I would recommend
reading all the books written by Dan Holohan see:

This link is broken, either the page no longer exists or there is some other issue like a typo.

My favorites are:
"How Come? Hydronic heating questions we've been asking for 100 years",
"Hydronic Radiant Heating - A Practical Guide for the Nonengineer
Installer", "Lost Art of Steam Heating", "Pumping Away", "Primary
Secondary Piping Systems"

The heating systems of yesteryear like your Aunt's have have changed
because of cost. You can not find a residential HVAC guy that can
thread pipe larger than 1-1/2 inches. They don't have the equipment and
don't want the job. America went to pressurized systems because of
safety. When all that vented water boiled off because of inattention
you had an explosion. Pressurized systems can move more heat (BTU'S)
through a smaller (i.e. cheaper) pipe. Gravity systems are obsolete
because it much cheaper to increase flow with a pump and use a much
smaller pipe (same BTU moved). The design is also forgiving, no
pitching of pipes, no multiple pipe sizes to control flow, etc. Solid
fuel central heating is making a niche comeback because it's 1/4 to 1/2
the fuel cost. Homeowners are driving this, not the fuel or equipment
industry. When is the last time you saw an ad for a coal boiler in a

There are a few anthracite stoker boilers still being manufactured,
Axeman-Anderson and the Eshland (now Alternate Heating Systems). There may be others. I don't know much about bituminous boilers and if stokers are available. Hand fired units certainly are. Modern electronic controls added to new, but old design coal boilers, make a world of difference in efficiency and convenience. Send me a PM and I'll send you my phone number if you want to call and talk about it.

Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea