Harmon or US Stoves

Modern and vintage hand fired coal stove are similar to a wood stove and in some cases can burn either. They need to be regulated and fed by hand usually every 12 to 24 hours depending on your usage. They require no power to operate making them ideal for rural settings with long power outages.
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Pa George
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Post Wed. Dec. 06, 2006 9:31 am

I am looking at buying either a Harman or US Stove add-on wood/coal forced hot air furnace. I would like some feedback from those of you that have use these companies units before.

I've had a Harman hot water coal unit before and it worked great. Paralleled it to an oil boiler. I know the hot water unit I had came with an automatic draft control (through the ash pan) and an overtemp control which kicked on one of the circulating pumps (zone) to bleed off heat so it never got too hot.

Do either of the warm air units come with features like this? Do they burn well or are they hard to maintain a fire in. My old water unit was quite easy to keep burning.

Thanks in advance for the feedback. :)

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LsFarm
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Post Wed. Dec. 06, 2006 10:04 am

Hello George, and welcome to the forum. I personally would recommend a coal boiler and use a water-to-air heat exchanger to put the heat into the furnace duct system.

This provides at least two advantages. One, much more controlable heat, with the ability to absorb extra heat in the water as the coal fire backs down [when the house thermostat is satisfied].

Second, a built-in hot water source for domestic hot water. Do I hear unlimited hot water, 45 minute showers and laundry at the same time??

The system you described is usually called a heat-dump system, and it is in place in most boilers, and big furnaces. You have to be able to shed the excess heat when the coal fire is trying to make max heat, and then suddenly the demand for heat is shut off [thermostat satisfied]. The coal fire can't just turn off like oil or gas.

In a hot water system the water can continue to absorb the heat from say 150* water all the way up to 220* water, That 's a lot of BTU's. In a furnace, the fan will have to keep running until the temp of the heat exchanger drops to a safe level to prevent damage from overheating. This means the the house will get way too hot just when you don't want it to get warmer.

Here is a thread with lots of links to boilers and heat exchangers:
Help With Considering a Coal fired Furnace

The US Stove units are wood/coal units right?? I would shy away from these, unless you want to be able to burn wood too. The compromises for burning wood often greatly affect the quality of the coal-burning experience. I made my boiler to burn both, I REALLY wish I had built it to burn just coal. I've had to learn and modify a lot to make up for the compromises made for wood-burning.

There are several high quality coal units that can burn wood, the emphasis on burning coal very well. Not visa-versa.

Hope this helps. Greg L
Burning Pea/Buckwheat through an antique stoker [semi retired SSboiler],
Running an Axeman-Anderson 260M boiler burning Pea, About 150-250#per day
Farming, Fixing, Fabricating and Flying: 'spare time' what's that?

Pa George
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Post Wed. Dec. 06, 2006 2:44 pm

Glad to be here. Actually grew up in coal country (Scranton/Wilkes-Barre area.

So if I am right what your telling me is the get a coal fire boiler and place a coil in the existing ductwork?

Then I would need a way to turn on the fan when I call for heat so it would circulate through the house. I would assume I would want to have a separate thermostat for the coal furnace but be able to turn on the fan in the oil furnace so air would circulate.

Right now I have a oil warm air system. I want to parallel the coal furnace to the present system.

The one problem I will have is one furnace will be at one end of the house and the new coal furnace will be at the opposite end of the house. this is because of chimmey considerations.

Are there any diagrams that would show me a typical installation for this?

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Yanche
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Post Wed. Dec. 06, 2006 3:18 pm

Yes, you would put a hot boiler water to air heat exchanger in your existing oil furnace. This is common in large commercial office buildings. Hot water in winter, chilled water in summer. A standard HVAC air handler product. It can be placed in the return or supply of your existing furnace. Location of the coal boiler will not matter. You plumb hot water to the heat exchanger in insulated pipes controlled by a water circulator pump. A single high end programmable multi-stage heat thermostat with some external relays can handle it all. Automatic switching to oil back up should the coal fire go out can be engineered in. Have you considered heating your domestic hot water with coal? A coal boiler makes it easy and heating water with coal is cheaper that the common electric, gas or oil.

You will likely need to learn about the individual components of such a system yourself. Then contract with a HVAC contractor for installation or do it yourself. It's unlikely you will find a HVAC contractor that will engineer a system for you. What is really custom is the coal bin, coal feed (hand shovel or stoker) and ash removal. Every installation is different depending on the physical space and desires of the home owner. Since you grew up in coal country you know the work required. There is a lot of experience and help available on this forum. Search on my name for other postings that give the details.

Yanche

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LsFarm
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Post Wed. Dec. 06, 2006 4:55 pm

Hi George, actually because of your chimney considerations a coal fired boiler is about the only way to tie into your hot air duct system effeciently.

Your Boiler will use an aquastat to maintain an effective water temperature. Your regular house thermostat can control the blower on the furnace. The same call for heat from the thermostat could turn on the circulating pump to the air handler [heat exchanger]. So the thermostat calls for heat, the circulating pump turns on, heating the air handler, the furnace blower turns on, moving the heated air throughout the house.

Or you can have the circulating pump running continously [I would] they only burn about the same as a 100 watt light bulb.

You can have a low limit temp switch that would fire up the oil burner if the coal wasn't supplying enough heat.

To heat your domestic hot water, leave the circulating pump running all the time, and have a water-to-water heat exchanger plumbed into the water loop from the boiler, water/air exchanger, water/water heat exchanger then back to the boiler.

Through the other side of the water/water exhanger run the cold water supply to the domestic water tank. Then any time you run hot water, the cold water entering the tank will be preheated by the exchanger. In my system the water entering my water tank is at 140*or more. I installed a tempering valve at the outlet of the tank to prevent scalding. ~115* is normal hot water.

Getting coal to your boiler in the basement: do you have an area that you could make into a coal bin? With an outside window or door access so that it can be delivered by a truck in bulk?? Or will you need to buy bagged coal, and carry it to the boiler??

If you can make a coal bin, then consider an EFM auger feed boiler, the only regular service will be emptying the ash pan every few days. The auger would feed the boiler directly from the coal bin. If you need to bring the coal in bags or buckets, then any of the hopper fed boilers will work great.

Hope this is helpfull. Greg L

.
Burning Pea/Buckwheat through an antique stoker [semi retired SSboiler],
Running an Axeman-Anderson 260M boiler burning Pea, About 150-250#per day
Farming, Fixing, Fabricating and Flying: 'spare time' what's that?

ktm rider
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Post Thu. Dec. 07, 2006 12:12 am

George I also have a coal boiler with forced air. The system works really well. I have an AHS Boiler and it allows me to burn wood also if I wish due to the unique grates in the boiler and it has two draft controls, one that drafts above the fire for burning wood and one below the fire for burning coal. Both draft systems can be shut off depending on which fuel you are using at the time.. . It burns both fuels equally well, but obviously I get more BTU's out of burning coal.

I agree with Greg, I would not waste my time ( or money ) on a hot air furnace when you have such an easy way of incorporating a boiler into your system. there are alot of advantages to a boiler over a hot air furnace like greg discribed.

All it would take is a heat exchanger inside your duct work and another thermostat that would only turn on the blower in your oil furnace. It doesn't actually run to the coal boiler its self. Unless you do not want to run your circulating pump continiously. I personally run my circ pump 24/7.

You would also already have a built in back up ( your oil furnace ) so, all you would need to do is set the primary therostat at say 72 degrees and the oil furnace thermostat at 68 deg. and then you would not have to worry about getting home in time so the house will be warm.
Father, Farm owner, Bow Hunter, GNCC racer

Pa George
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Post Fri. Dec. 08, 2006 12:47 pm

Thanks for all the help. Sounds like with a little research I can do this installation myself. I did the last one without any problem. Would AHS be the preferred supplier of the boiler. It sounds as if many here have used their boilers and are quite happy with them.

The boiler would be getting its own new chimmey. The oil one is a powered vented installation.

I won't be installing until 2007 (Spring/Summer) so I have plenty of time to work out the exact installation.

I definitely will add the domestic water heat exchanger to this system. I had a small pump running continuously on my last one since domestic water was heated by the the hot water oil furnace (no water heater tank) Never ran out of hot water.

mslagle
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Post Thu. Jan. 04, 2007 12:51 pm

George, I am just finishing up the install of a coal/wood combo boiler. The hardest part to this point has been the thermostat and the crazy furnace wire scheme, as I am using the existing furnace blower to force the air. Let me know if I can help with any questions. I know I had to do some searching to find all my answers. :)

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ktm rider
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Post Thu. Jan. 04, 2007 12:55 pm

If the final step that has you stumped is simply hooking up the thermostat to the oil furnace blower, I would just call an electrician or a friend who is an electrician. I'm sure the cost would be minimal and then you will know it is done correctly.. Just a thought..
Father, Farm owner, Bow Hunter, GNCC racer

mslagle
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Post Thu. Jan. 04, 2007 9:36 pm

I was almost to that point but I am working with a 24v system so I wasnt worried about my hair catching on fire. So here is what I found.

With a new style digital thermostat on a 24v system you need the G and the R if it is a battery powered thermostat. If the thermostat is 24v the you also need the common 24v or C.

Then it is just connecting wires.

G to G
R to R
C to C

If it is 110 I would talk to a furnace specialist.

dirvine96
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Post Fri. Jan. 05, 2007 9:00 am

what are you trying to do? Turn the fan on when the t-stat calls for heat. If so you need to connect the W (white) on the t-sta (heat curcuit) to the g (green) on the furnace (fan curcuit).

Don

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Post Fri. Jan. 05, 2007 9:14 am

If you looking for strickley hot air, I would recomend Harman. Best warranty, great dealer help,quality.

mslagle
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Post Fri. Jan. 05, 2007 7:08 pm

Don, thanks for the info. I looked at my t-stat and once again did not catch my hair on fire. Here is what I found, there is no W but I do have a W1, W2 and W3. I left it how it was G to G. It is working but I would like to learn more about my system.

Thanks for the help.

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