using my woodburner with my gas heater in series -having major problems

[Jolin]

Ok, I am having some serious problems, and I thought I would come to the experts to help me out.

First, my system is a hot water heater (i was told that it is a heater because it heats the water and the water goes throught the lines and radiates fromt he radiator, as opposed to sending steam out -boiler) that has 3 series of loops that run throughout my large, old farm house. The 3 series throughout the house are not partitioned off very well (meaning that one loop goes through out the house in no organized way, making it difficult to section off the heat ).

About 2 years ago I built a small shed outside about 30 feet from my house, and installed a used, Jensen woodburner and ran the 3/4 inch lines underground to my house.

The Jensen woodburner is an older model, with just a small dampening door on the front of the main door of the burner.

I have the water lines from the burner going to the return line of the gas boiler so the gas boiler recognizes the water already hot enough, therefore not using gas to heat the water. That way, if I am not using the wood burner, the gas furnace can still heat the water.

All seems fine so far (at least to me). The problem I have is that this system is not effcient. If the house does not call for heat, the the water just stays in the tank at my woodburner and is constantly being heated. Then, when the house calls for heat and activates the pumps, it sends the "now too hot" steam into my lines in the house, and sounds like people are banging my water lines in the basement.

I guess I am seeking the best, most efficient way to use my woodburner as a supplement to the boiler I have in the basement.

Also, I do not have any duct work in my house.

any help, diagrams, info, websites, etc. would be greatly appreciated.

thanks, joe

[email protected]

 

[Eric Johnson]

I have a similar setup, Joe, although mine works pretty well. Are you saying that the pump only kicks on when a thermostat in the house calls for heat? Mine is set up so that hot water from the wood boiler circulates to the gas boiler through a heat exchanger when the water in the wood boiler hits the aquastat set temp. So, as long as I have 160-degree water or hotter in the wood system, the pump is circulating it and heating the water in the gas boiler. When a stat in the house calls for heat, water is distributed to the zones (with other pumps) from the gas boiler into the radiators.

When there's no call for heat, both boilers reach the temp set by the aquastat that controls the blower on the wood unit. So, if the aquastat kicks the blower off at 190 and water circulates for long enough, both boilers have 190 degree water. When the blower shuts off, it pretty much puts the wood boiler in stasis.

Do you have a heat exchanger, or do you just pipe the wood-heated water directly into the gas boiler vessel? Do you have a flow check valve on the system so that you don't get reverse circulation, where the gas burner is heating water that's then circulating back into the wood boiler. That's can be major source of inefficiency, alhtough I know that's not the problem you are talking about.

I guess a few more details such as how your aquastats are set up as well as some info on the pumps and piping would be helpful. Doesn't sound like a major problem, but I suspect you have a flaw in the way your system is currently set up.

If your problem is that you're overheating both boilers, then you need to take a look at the wood system air control, and maybe consider installing some heat storage in the form of a water tank that you can heat now and use later.

 

[Jolin]

thanks for the reply.

To be honest, I do not know much about either boiler. The wood boiler is hooked right in line with my current system, and does not go to the boiler directly. It just goes into the copper line right before it goes in the return. I like what you were describing with your system. I guess I should read up on my boiler.

I have a pump at my gas boiler, and a pump at the wood boiler. My wood boiler's pump is hooked up to the same control as my gas boiler. Both pumps turn on at the same time, so that one pump isnt doing all the work. I have it hooked up as one series. From what you are telling me, it sounds like you have to systems. One from your gas furnace to the house, and one series from your gas boiler to your wood boiler.

I did notice that there is somewhat of a blower that is not hooked up towards the bottom of the back of my wood burner. I will have to talk to the guy that I bought it from on how to work that. I am assuming that that has something to do with the temperature control within the boiler. I am sorry if I am sounding confusing.

I could make some kind of diagram and try to post it on here. Is that how I attach it by the bottom? does that apply the picture right to the post?

thanks again.

joe

 

[Jolin]

I have been reading up, and no, I do not have a heat exchanger. I have attached a picture of a diagram that I got from www.centralboiler.com. Is your system similar to this? does your wood burner heat your hot water tank as well?

 

[Eric Johnson]

I don't think the pumps should both go on at the same time. It sounds like what's happening is that the wood boiler is overheating because there's no circulation when the house stats are not calling for heat. You would be better off, (based on my experience only and not any formal training or education) to wire up the pump at the wood boiler for continuous operation. The right way to do it would be to put an aquastat in the wood boiler (or wire up one if it's already on there), to control the pump. You need an aquastat that "makes on rise," meaning that it turns the pump on when the temp gets to a set point, say 160 degrees. This is especially important since you are only using 3/4-inch pipe, since that makes it more difficult to quickly dissipate the heat from the wood boiler, which is what the current set-up is asking it to do.

Re-wiring the circ pump in this way will, as I said earlier, allow the water in both boilers to rise and fall more or less together, except that with the aquastat, the gas boiler (which is where your house is drawing its heat from) will not drop below the set-point. Actually, it will by about 15 degrees, but that's not the issue. When the circulator pump shuts off because the temp in the wood boiler has dropped below, say 145, then it has time to catch up and you can still draw hot water from the gas unit. And when all else fails, your gas boiler kicks on and keeps it nice and warm.

That's my suggestion anyway. I guess I should have asked upfront what the problem is. Are you burning too much wood, or not getting enough heat out of the system, or burning gas, or is everything going OK but the banging of the pipes disturbs you?

And I would check out the deal with the blower mount, even though it sounds like the boiler is working OK.

I do heat my domestic water. My set-up looks a lot like that diagram.

Hope this is clear. Let me know if it's not and I'll try again.

 

[Jolin]

yeah, thanks again for the reply.

What ever you said sounds like my problem. For one, I dont have a heat exchanger, and my system looks nothing like that. Now, in the picture, where does your gas system go in the series?

Is there a place that you recommend getting the parts to make my complete system? also, do I need a special heat exchanger if I want to hook it up to my hot water heater?

there are a few places in the diagram that I dont understand, as too what the parts are. I will circle them on this next picture. (the one I circled says its the "mixing valve", and that kind of confuses me.

again, I appreciate all the info that you have given me.

 

[Eric Johnson]

Joe,

Something wrong with the image file.

Anyway, yes, you need a heat exchanger to get the domestic hot water. It's really just a zone that you can build into your current distribution system. I have what's called a "side-arm" heat exchanger. It works on gravity, i.e., it hooks up to the water heater so that water from the boiler heats a 3/4-inch core. Just a little pipe containing the domestic hot water surrounded by a bigger pipe (1 1/4 to 1/1/2-inch copper) through which flows hot water from the boiler. As the water in the small pipe heats, it rises and circulates hot water into the water heater. Pretty neat. They cost about $150 from places that sell outdoor wood boilers. I made my own out of some spare parts, but the ones you buy are more efficient because they use a special, high-surface area core. The mixing valve is just a valve that mixes the hot water with cold water so that the hot water coming out of your tap stays hot but not super-hot. There's a great thread here talking all about it and with some great ideas from other members. Look around, it shouldn't be hard to find.

You can get everything you need (aquastat & well, piping & fittings at any good plumbing/heating supply place. The crappy ones probably have the stuff as well). Some wiring, you know, the usual stuff. You probably shouldn't tackle the job yourself unless you're comfortable with wiring and soldering pipe. The aquastat, with the right well, will probably run you $75-$100. If you knew exactly what you were looking for, the cost on Ebay would be about half that.

What I do is circulate hot water from the wood boiler through a heat exchanger connected to the gas-fired boiler. The reason I have a heat exchanger is that my boiler is out in the barn and most of the piping is above ground. So it's full of glycol so it won't freeze if I ever have to shut the system down in the winter. Since I have a big old house with radiators, it would cost too much to put glycol in the whole system. I would rather direct-pipe the water from the wood boiler because I think that would be more responsive and efficient, but life is full of compromises.

Basically, my system is as described earlier. I have a big pump that kicks on at about 160, and keeps all water above that temp circulating through the heat exchanger. I have another pump wired to the same aquastat, that circulates water from the gas boiler through the other side of the heat exchanger. They both go on at the same time. My boiler has a blower wired through another aquastat (this one "breaks on rise") that kicks it off when the water temp in the wood boiler hits 190. Tonight I have it turned up to 200 because it's below zero outside.

 

[webbie]

Joe,

I have a big pump that kicks on at about 160, and keeps all water above that temp circulating through the heat exchanger. I have another pump wired to the same aquastat, that circulates water from the gas boiler through the other side of the heat exchanger. They both go on at the same time. My boiler has a blower wired through another aquastat (this one "breaks on rise") that kicks it off when the water temp in the wood boiler hits 190. Tonight I have it turned up to 200 because it's below zero outside.

Boiler installation is deceptively simple - one hint would be to see if you can buy a manual for an HS TARM MB55 (this is a natural draft boiler) from TARM USA. They surely have them, and this at least gives you some diagrams, etc.

I generally used a parellel setup as opposed to series, which simply means:

1. The two boiler are hooked together with an additional circ.
2. The circ turns on whenever temp at wood boiler hits about 185 and off at about 165 or so.
3. Turn down control on gas or oil boiler to about 160, it will then not turn on unless below that.
4. Have an "overheat" aquastat that automatically jumps one of the thermostats if the water temp gets about 190 or so....

Now, some other thoughts - The Jensen does not hold a whole lot of water....your gas boiler may not also. This means the system cannot store much energy and can easily overheat.

Solutions:
1. Additional storage tank to hold hot water
2. (suggested) 4-way mixing valve installed on one or more of the larger and most used house zones.

The mixing valve varies the temp of the water delivered to the house slowly, so the house can act as part of the storage system. It is a great addition to any hydronic (hot water) system.

The TARM manual should mention these, and there should be lots of other info on the web about them.
http://www.honeywell.ca/water-controls/products/v5442.htm

Good Luck

 

[Jolin]

thanks again.

so the heat exchanger is actually a 3/4 inch pipe that goes inside a bigger pipe that contains the hot water? So it keeps both water systems seperate?

so do you have 2 heat exchangers? one at the hot water heater, and one at the gas boiler? so that the wood burner heats both? or do you just have one. If the wood boiler is not on, does the gas boiler heat your hot water heater? thanks again for any info. It would be great if I could just talk to you on the phone. If your ok with it, my cell is 319-750-3499. Or I could call you. Its free for me past 9.

thanks again, I think I am pretty close to understanding.

joe

(broken link removed)

 

[Eric Johnson]

Craig knows a lot more about this stuff than I do.

The Tarm installation manuals are $20 and you can order one over the phone. They also have some basic installation diagrams on their website, tarmusa.com.

But to answer your question, yes, I have two heat exchangers. One is a flat plate exchanger to get hot water into the gas boiler for distribution up into the zones. The side-arm water heater takes the same water coming in from the wood boiler and passes it by the domestic hot water inside the heat exchanger. Both recover whatever heat they can as the water circulates through them and back to the wood boiler. It doesn't sound like you need a flat plate heat exchanger, which is good. I switch the gas boiler off in the Fall and don't turn it on again until late in the Spring. I don't want it kicking on at all.

My problem is not overheating, it's getting enough heat through the heat exchanger. I recently wired the zone circ. pumps through an aquastat on the gas boiler so that the pumps won't kick on until the water temp hits 140. They pump water into the house until the gas boiler temp gets down to 115. That allows the system to catch up on cold nights. It was set up so that the house zone pumps turned on whenever the stats in the house called for heat, regardless of the temp of the water being circulated. I didn't think that was terribly efficient.

 

[BrotherBart]

Ya know. Reading all of this technical stuff I am starting to love my dumb old wood stove and electric water heater a whole lot more.

 

[Eric Johnson]

It's like anything else, BB. If you're into it and like fooling around with this kind of thing, there's a lot of satisfaction in making it work.

It reminds me of waxing cars. Some people really enjoy it. Me, waxing a car is about the last thing I'd choose to do on a nice day. Now splitting firewood, that's a whole different story.

 

[BrotherBart]

It's like anything else, BB. If you're into it and like fooling around with this kind of thing, there's a lot of satisfaction in making it work.

It reminds me of waxing cars. Some people really enjoy it. Me, waxing a car is about the last thing I'd choose to do on a nice day. Now splitting firewood, that's a whole different story.

I understand completely Eric. When ya got something ya love ta do it is great. And if it keeps ya warm too, fantastic.

I remember well when I would come home every day after work and either grab the chainsaw or the maul. 12 months a year. In fact when a nasty one was at hand I would drink a beer and circle it a few times every night. Then one night I would come home, change clothes and start touching up the chain. My wife would come out and say "Ok, it's going down. The number is still 911 right?"

The most famous one it was a 94 foot red oak that had split down the middle to within eight feet of the ground. Huge springs left and right. Everybody knew it was coming and when Old Yaller fired off people showed up from half the neighborhood just to watch me get killed. I put that sucker on the wood pile.

Now it is just work. Old ya see.

Keep having fun buddy and be safe.