Thanks Boiler Room! My Tarm is up and running

[oldmilwaukee]

I just got my Tarm Solo 40 Plus up and running! I have 200 yards of concrete in my basement that was at 40 degrees so it's going to take a few days to get this place real cozy, but I'm already up to 66 degrees! (new construction, but I've been working on this house so long it feels like old construction) So far I love it.

By lurking here, I learned several things that changed my design and installation for the better.

primary-secondary piping... thank you boiler room.
WILO stratos ECM pump... thank you for the knowledge of its existence.
Superstor 60... didn't know what an indirect water heater was 3 months ago.

Next season I might be ready to try 1,000 gallons of water heat storage
and turbulators... and... and... there's a lot to absorb here.
Seriously, thank you to everyone who posts here.

-Thomas

 

[hoth2oguy]

Congratulations Thomas! Great Blog too!

 

[Duetech]

Really nice blog. Best to you and yours. Off the grid too! Sweeeeettt!

 

[Jackpine Savage]

Congrats! That is a nice blog and a beautiful home. You do nice work.

 

[f3cbboy]

congratulations on getting yet another project finished in your home. The blog is really pretty amazing!!

 

[sweetheat]

Hi Thomas: I'm sure your happy you have your Tarm assembled and working. Mine has exceeded my expectations. Your house blog is my house blog of 25 years ago! alas no blogs in the 80's. You have written it for me. Not quite the same but I do love my warm timber frame home and my Stanley wood cook-stove. I stayed on the grid because of cheap power then and a large assortment of woodworking power machinery. My daughter and son-in-law are on my same road and off the grid completely. They are building their house as they go also. A Stanley wood cook-stove is going to be installed in their home too. As soon as more stone chimney veneer gets lay-ed up. Sweetheat

 

[Jim K in PA]

Congratulations Thomas. You know I have been following your blog for a few years now. Great work, as always. :coolsmile:

 

[oldmilwaukee]

Thank you guys for the kind posts about my blog. It started out as a way to update the family on my house project without clogging their email boxes with jpgs. I found that if I updated them more frequently, they were less likely to ask "d'ya move in yet?" The project has gone on so long that I go back and read the blog from 4 years ago to remember how or why I did things a certain way. It can also serve as an online repair manual for whoever lives here 50 years from now.

Sweetheat, maybe we are living in parallel universes, 20 years out of phase. Today we cooked chilli on the Waterford Stanley while the Tarm chugged away silently in the basement. With warm floors at our house site, we will no longer feel bad asking folks to take their shoes off when they come in, and maybe we can get the place almost clean enough to live in.

Chris, I think it is a tribute to your company that you participate in these forums and respond to emails. I am really impressed with the unit. I think if there were more people familiar with how to install them properly and if more people knew about them, they'd be everywhere. Like my off-grid solar system, when I quit paying attention to it, that will be a sign that it's really doing its job. It will be several days before I quit opening the "blast door" every hour just to look at the 2000 degree flame! (sorry, can't help myself... I just can't get enough joy through that foggy little round piece of pyrex in the door)

oh oh - my back-ordered BioHeat Ash Hod just showed up from the UPS man! Gotta go see what an Ash Hod is.

-Thomas

 

[Hankovitch]

Hello Thomas,

I am SO happy for you. Very interesting....I just found this. I have some questions for you. It appears that you did not put insulation under the basement slab. Is this correct?
Is this because you insulated the walls of poured concrete?
Did this insulation of the walls make it unnecessary to insulate under the slab?
- I did a quick scan of your blog and did not find where you addressed this, if it is there just direct me to month/year for me to read.
I ask because we have a barn (in SW Wisconsin) which we will convert into our home. 36'x104' footprint. Hay mow is 25 feet from hay mow floor to barn roof peak.
First floor of the barn is the former milking parlor - 12" thick concrete walls up 8 feet, footings go down nearly 5 feet below level of the milking parlor floor.
We will use 3" of Sprayed Polyurethane Foam on the OUTside of the barn, from peak to ~4 feet below grade. Will this be sufficient to allow the entire structure to function as a huge heat sink (as it appears to me you have done) if I put in-floor radiant heat tubing into the newly poured concrete of the new First floor of the barn/home?
And then I will NOT need foam under the slab?

Sincerely,

Hankovitch in SW Wisconsin

 

[oldmilwaukee]

Hanko,

Excellent question. How effective will the earth work as a heat-storage medium? I have not yet addressed this on my blog, but I have been thinking about this every night for the past 3 days. (and the internet is full of conflicting "facts") Take everything I say with a grain of salt, and realize that every situation is unique, but I took a BIG gamble (when I poured my foundation 2 or 3 years ago) that I can use the earth to store heat if I accept that I will lose some portion of that heat. My basement is 2,200 square feet, and I ran pex in one half of it (the other half is garage that will only get misdirected heat from the first floor pex and from the heated half of the basement if the door is open to it.) I insulated the outside of the basement walls on the half that I plan to heat. (4" of blue foamboard from the footer to the bottom of my SIPs - 9 feet in height, 7 feet of which is below grade) Also, on this half of the basement, I insulated under the edge of the slab 2 feet in, with 2" blue foam. The edge of the slab is isolated from the walls with 1/2" open foam zip-strip type expansion material. I value structural integrity over energy efficiency, so my footers (30" wide and 18" thick) have no insulation beneath them. (I know, I should draw a picture - I will do that and post it if I can find some more time.)

As I type this, my Tarm is on about its 9th load of wood and the 1,000 square feet of slab I am pumping heat into will still soak up almost all 140K BTUs w/o letting the boiler idle down. That could be good... or that could be bad. If this is still the case one week from now, then I'm going to have to start wondering if the earth is just a big heat-suck! (Of course, I am pumping heat into the 1st and 2nd floors too, but every now and then, I send all the heat to the basement slab to see if it will still take all the Solo 40 can put out - so far that is still the case and the basement slab is up to 72 degrees I think.)

Here in KY, the soil below a certain depth is 59 degrees year round. Our frost line is 24 inches deep (although the ground rarely freezes below one foot). One of my motivators for not insulating beneath the entire slab (and leaving half the basement uninsulated) was to maintain the natural cooling benefit of the earth. (taking advantage of the heat suck effect). I wasn't living in the house this past summer, but the basement was really comfortable when I was working here. One neat thing I realized just the other day is that I can run my radiant circulator pump in the summer (not the boiler circulator), and possibly bring some of that coolness out of the basement up to the first and second floors. Once it reaches steady-state the water will probably not be cool enough to make the lines sweat, and the cooling effect will be minimal. I'm thinking maybe 4,000 BTUs of cooling. But that ain't bad for running a 50 watt circulator pump. Its free to try because my system is built like it is. I will post something on my blog if it works (or if it fails).

FWIW, if it works one way it will unfortunately work the other (such is nature) - I think I'm going to lose about 4,000 BTU/hr (maybe double that?) in steady state if I try to store heat in my slab by keeping it at say 80 or 90 degrees. It could get really warm down there too!

I am dying to know the answer to a question that I had to guess at 3 years ago when the slab was poured. I should have a clue by the end of this month. Even if you insulate beneath your slab, it sounds like you're going to have lots of wonderful thermal mass in your setup with all that concrete.

-Thomas

 

[Hankovitch]

Hello Thomas,

Thank you for your nice reply.
Some of what you mentioned I have seen....for instance, I have seen it mentioned that when you pour a slab one possibility is to insulate in from the walls several feet, and leave the remainder (center) of the slab area un-insulated. With the apparent wisdom of using the earth in the center as a huge heat sink. I imagine someone out there must have done the experiments to determine if it is wise(r) to insulate under the entire slab or leave the center uninsulated.
I imagine that if one can insulate the walls-and-outer-foundation with a few inches of water-impermeable insulation (your Blue Board), insulation going below frost line, then what you've done could be excellent.
Whereas if your walls-and-outer-foundation are uninsulated and therefore in communication with the sometimes frozen ground, then one could lose a lot of heat by conduction from heated slab to unheated concrete to frozen ground.
In this case of uninsulated outer foundation/wall it would likely be wise(st) to make sort of huge tray of water-impermeable (foam) insulation (foam over compacted gravel/sand, AND foam up the inside foundation wall to where the level of the floor will be --- now I need to draw a picture!)..... then add rebar over the foam, the add the in-floor radiant tubing, and pour the floor slab into this huge foam-insulated tray.
It will be very interesting to read what you find out a few weeks from now.
I sent links to this thread and your blog to my wonderful wife - I am certain she will find what you have done as interesting and educationally worthwhile as I have.
We will soon be having our in-floor radiant heat designed for us. I hope to be able to get well-reasoned answers to these questions from the people who will be doing the design. Apparently the people we have enlisted are quite knowledgeable. I will keep you informed as I get replies.

All 4 now,

Hankenstein in SW Wisconsin

 

[oldmilwaukee]

I think I follow your tray idea - sounds like it should work. If you had the room, you could even fill the tray with a thick layer of sand or DGA before you pour your concrete into it to give you more thermal mass at 1/10th the price of concrete.

We had a wind storm that knocked out the town's power so my wife and kids and I are all at the house site today enjoying the 73 degree temperature. I still have the boiler running wide open, and still pumping BTUs into the slab. The leaving temperature is 140 and the return temperature is 100, and I estimate the flow through those slab loops to be a total of 5 GPM. That works out to 100,000 BTU's still going into the slab. Of course, some of this (1/3?) is going into the house, but a lot is still going into the ground. I'll keep you updated. (FWIW, the outside temperature is 43 degrees here and windy and I'm heating a little over 6000 square feet.)

My parent's house (the one I grew up in) has radiant heat from the 1960's, built by my grandfather (he passed away in the 70's). It's a brick house built on a slab. Amazingly, the radiant heat still works, as does the original NG boiler. I am pretty sure there is zero insulation anywhere in the ground, and the boiler obviously isn't very efficient. There is no mixing valve or anything to temper the water before it goes in the slab. All of the valves are gate valves, and the B&G;pump has a motor the size of a paint can. No air separator/bleeder anywhere. I don't know how the radiant heat still works - the slab has 1/8th" cracks here and there, but I guess the copper pipes just stretched with the slab. However you build your house, don't skimp on rebar in the slab - I'm sure that's all that's saving thier embedded copper pipes. The house is not very efficient to heat. I have recommended that they dig around the perimeter of the house (down to the footer... 2 feet?) and put some blue board foam in. I think this would really help their efficiency. Next step would be to buy a new boiler - even a cheapy would be better than theirs. After all, their boiler is 50 years old and about twice as big as it needs to be.

After I posted last night, I remembered that my main motivation for not insulating under the slab of our house was to get the benefits of summer cooling from the earth. You are considerably further north than me, so you objectives may be different. July and August here are very hot and muggy. If your radiant experts tell you to insulate under the slab, I would follow their advice, seeing as you probably don't need the natural A/C. The incredible thermal mass of your new house would probably coast you through the few abnormally hot days you might get there in the summer. Just another thought.

 

[starksb]

Did you put blue foam under your footings?
Thanks

 

[Jackpine Savage]

From what I've read, two big variables in deciding whether or not to insulate the slab are soil type and the water table level. If you have clay type soil and/or a high water table, the heat losses could go way up. Here's one thread I remember reading. In my opinion NRTRob knows his stuff. I ended up getting them to design our radiant system.

http://www.greenbuildingtalk.com/Forums/tabid/53/forumid/12/postid/23503/view/topic/Default.aspx

"Whether you need slab insulation or not depends. You most definitely need insulation on the vertical outside edges of your slab. That is a significant source of heat loss. You also need to insulate the outer 5' perimeter of the slab, where it is still seeing higher loads from the surrounding ground surface.

As for the center of the slab, if your ground is clay, rock, or wet, you definitely want to insulate fully. Those conditions can make for a heck of a heat sink. I saw a slab up here in maine (built on ledge, which is everywhere up here) that literally could not maintain temperature in the spring when the ground was wet. wicked all that heat right out.

If you have good natural drainage, no standing water, no high water table, and good loose or sandy soil, then you could get away with less or no insulation in the center of the slab. If you're in doubt though, you should insulate. That's not an easy mistake to fix later. You can replace windows.

Even in that case though, you do lose heat to the ground unless you are maintaining ground temperature or lower for a slab temp. Perhaps not enough to pay for the added insulation quickly.. but something, yes.

We generally go with a reduced center insulation or none only on very large slabs (where it's mostly center area), or in mild areas with the above noted soil conditions. In a normal residential slab, I don't think it's worth trying to "play the dice" there unless you are very sure of your soil conditions year-round and your water table. And even then, you're not going to save that much since the perimeter and edges still need to insulated, no matter who or where you are.
"

 

[oldmilwaukee]

Starksb, I did not put insulation under my footings. It would stand to reason that some heat is going down the basement walls and out the footers. That would be one easy path for it to flow, since the outside of my basement walls are insulated, and the basement walls rest on the footers.

I'm on clay soil with an occasional layer of siltstone. The earth here is very dry. When they drilled the geothermal wells, it was 100 feet before they hit water. To be supersafe, when I put my foundation in, I put french drains inside and outside of the footer and ran them to daylight. It could help with surface runoff and radon (although no one here worries about radon). My house is on a knoll, so it was possible to run the drains downhill and still hit daylight.

For me the thinking was "don't insulate under the whole slab, burn a little extra wood every winter, but get a nice cool basement in the summer even if the A/C isn't running." But again, that is a KY point of view. I lived in NH for several years, and up there, I probably would have insulated under the slab since summers there were quite bearable.

 

[Hankovitch]

Hello Thomas, Oldmilwaukee and Jackpine Savage,

Thank to all of you for your inputs, and for the link to another thread on insulating a slab.
Very worthwhile information in what you've written.
Our farm is in a wide, low, level valley. There is a small river running through our property, and on part of the property this river forms part of our property line. I recently used the Bobcat 'pallet fork attachment' with only one fork on it, and dug down at a random location adjacent to the foundation. The clay soil was wet all the way down. Looks as if the wisest thing to do will be to make that insulated tray, add rebar, add radiant tubing, and pour concrete. I WILL first remove the existing floor - once I've done that I will level things off with a Compacter, and put down a layer of 2" thick blue board. I will likely have them apply ~1 inch of SPF over the Blue Board and up the concrete at footings and up the concrete at the perimeter to make that 'tray' mentioned in an above email. Then add the rebar, tubing, concrete.
I believe I will go with your idea Thomas, and err on the side of structural caution - and not insulate under the footings for the newly located posts which will be placed every 8 feet or so down the 104 foot length of the barn, and will be holding up the 5 sistered 2x12s, making the 'beam' which runs the full 104 foot length of the barn, and holds up the Hay Mow (the future living space of the barn/home). I believe this should give me good strength and sacrifice only marginal heat loss. And, since it is an existing structure I will just have the backhoe operator dig down about 4 feet (footings for the 12" thick concrete barn wall go down at least 4.5 feet below barn's 'ground level' floor), clean off the concrete, and apply 3" of SPF, then back-fill. I won't have the awesome 7 feet below grade insulation you have Thomas (how GRAND), but at 4 feet is IS right at the agreed-upon frost line for where we live in Wisconsin.
Thomas, I see you mention you have 4,000 feet of Radiant Pex...we will have something similar. Did you put radiant floor heat in all levels of the home?
I am thinking of having the Pex in all levels - what do you think?
What did you do?
And why?
First floor (former milking parlor) will have 3 zones - ~20 to 25% at each 'end', and 50-60% in the middle.
One end will be garage bays, other end will be horse tack and horse grooming area (no stall), middle will be workshop and access to the attached structure where we will house the GARN WHS2000.
Second floor - main entry, kitchen, dining, great room....all open, bath, study, game, office.
Third floor - loft; bedroom 1, bath 2, bedroom 2, master bedroom with bath 3.
I am unsure how to do the zoning on 2nd and 3rd floors....but our radiant heat design guy will educate us. He has been doing this for systems using a GARN for 20+ years, and has (in his words) people 'bordering on brilliant' when it comes to designing radiant floor heat systems with the GARN..... as backup for when he is stumped.

Sincerely,

Hankovitch in SW Wisconsin

 

[oldmilwaukee]

and not insulate under the footings for the newly located posts which will be placed every 8 feet or so down the 104 foot length of the barn

Hanko, to support the loads of the posts in my basement, I used plinths that bear directly on the footer beneath. You could do this as well. Less chance of cracking your slab, and if you put 1/2" of expansion material around the plinth before pouring the slab, the plinths won't steal as much heat from your slab and send it to the footer. I'll try to attach a picture.

I know my blog is unwieldy to navigate - here is the post I did on the slab pour. archived article on radiant slab pour I do mention and show the radiant heat tubes, but I think I failed to mention anything about insulation.

I won’t have the awesome 7 feet below grade insulation you have

20% of my basement walls are "walk out", so the ideal 7' of insulation does not apply there! This discussion we're having has reminded me that I should put down at least 2 feet of the 2" blueboard horizontally underneath this walk out area. It would be sandwiched beneath the "patio" and above the outer lip of the footer.

Did you put radiant floor heat in all levels of the home?

I did half of the basement, all of the first floor (great room, kitchen, master bedroom), most of the second floor (included 4 bedrooms, omitted loft above kitchen), and none of the third floor (one bedroom, a loft, and an office type area). The house is very open and I thought it would be a waste of time and money to heat the common areas on the second and third floors - today I am typing in an area w/o pex on the second floor and it is very comfortable. I figured enough heat would rise to the third floor and that seems to be the case too. It's mild outside (40 degrees), so I need more data to confirm that it was the right decision to omit the third floor.

unsure how to do the zoning on 2nd and 3rd floors

I put them on Mr. Pex manifolds, and ran thermostat wires to each of the bedrooms just in case. Right now, it's one big megazone and there's not 2 degrees difference anywhere in the house (except the basement which is the warmest place in the house). But I don't have doors hung on most of the rooms yet! Wirsbo and Mr. Pex and several other manifolds make it trivial to individually zone your loops later if you want to defer that decision. The one caveat is you probably want a delta-P based pump that will respond intelligently to zone valves opening and closing if you add them later.

Almost forgot... regardless of where you decide to locate the pex, make sure there's enough tubing in the house to transfer all of the BTU's you will need to heat the house. 30 to 40 btu/ft^2 seems to be the internet consensus on the maximum transfer you can get from pex radiant tubing. Maybe a little more for concrete, and likely a whole lot less for staple up tubing w/o aluminum plates.

 

[Jackpine Savage]

If you are going down to the joists and installing subfloor for your remodel, one product to look at is Warmboard . I think it stands head and shoulders over the other alternatives, but it isn't cheap. I ended up going with aluminum extrusion plates under our existing subfloor.

 

[oldmilwaukee]

I agree, Warmboard looks like it would outperform anything out there where concrete is not an option. But I priced it 2 years ago and I think a 4x8 sheet was about $130 - it was going to cost over $10,000 if I used it. I just couldn't cost justify it for myself. One minor thing I did not like about Warmboard was that if you should ever have a leak it meant pulling up finished floor to get to it. Also, in my case, I'm already going to have to move some pex to accommodate the A/C ductwork. I know, bad planning on my part, but if I had used warmboard it wouldn't have been as easy to reroute the pex.

 

[Hankovitch]

Hello again all…....
I am posting this in a second thread, please accept my apology if you are reading it twice.
I hope you will see its value.
Hankovitch here to report on what we’ve done so far on our Barn-to-Home conversion project. We decided to “go” with the 3” of Close Cell Polyurethane Foam on the outside of our barn….from 3’ below grade (wanted to go 4', but couldn't) all the way up to the peak of the barn, and back down the other side once again to 3’ below grade. A monolithic application of 3” thick foam on the barn, outside, covered with a polyurea paint as final coat to protect from UV light and the weather. Essentially as they re-did the Superdome roof after Katrina destroyed the EPDM roofing. We are doing this in stages, and I report here the current state of the project and what I will call the results.
We have dug out around the foundation of the 36’ x 104’ barn, 4 feet down…..pressure-washed the dirt from the foundation/footing……then applied 3” of SPF to the foundation (down 3’ below grade), and applied 3” of SPF up the 8’ high, 12” thick concrete wall of the milking parlor and up another foot……then sprayed a polyurea paint over the foam…..drain tile was put in around the foundation and runs to one of our ditches 300 feet from the barn……then we back-filled where they dug out around the foundation………then we also applied 2” of SPF inside the barn, to the milking parlor ceiling (underside of hay mow floor)………..we put 14 new windows, 3 new doors, and a new 7’x9’ garage door in each end..………
In this 3,500 sq foot area (the former milking parlor) the only source of heat is passively from mother earth…down 4 feet the temp of the earth is approximately 50 degrees F…..
Bottom line on how well the insulation is working.
Since Jan 1, 2010 outside temp has ranged from +39 F to -14 F.
During that same time period the inside temp of the former milking parlor has ranged from +33 F to +37F.
The important thing to note is that, even though the outside temp dropped to 14 below zero, the inside temp always stayed above freezing….on some days inside the milking parlor has been as much as 47 degrees warmer than outside!
Note, this is with PASSIVE geothermal heating…..we do not have a heat pump, there is NO source of ‘heat’ for the barn other than what mother earth supplies by heat passively (and continually) coming up through the concrete slab of the milking parlor floor!
Furthermore, there is no ‘earth berm’ of the barn, the entire milking parlor is above ground.
Pretty awesome, I’d say…..

And, it will only get better as we…
- put on storm doors (for the three doors we put in),
- complete the back-filling (in some places the back-fill is over a foot low), and
- close off the openings of the two stairways (at ceiling of the milking parlor) with something better-insulating than the 3/4 OSB we now have covering the openings.

By the way, I’d love to hear how things went for the fellow who started this thread. What do you have to report, now about a year since the thread started?!

Sincerely,

Hankovitch in SW Wisconsin.

 

[oldmilwaukee]

Whew! I'm ready for this winter to be OVER. What I've learned...

Seasoned wood. Seasoned wood is the key. I ran out mid winter, so I've had to experiment with "less than optimal" wood sources. I cut and split some old (4 years old) yellow poplar logs - they didn't burn worth a squat. Same for a standing dead white-oak. I split the wood down to really small pieces and stored it in the basement for 2 weeks, and it would barely produce heat. I did cut a standing dead chestnut oak that worked out OK. But here recently, I went to my snow covered construction scrap pile and cut some oak 3x3's and 1x12's and 2x4's. Even though they were still a bit damp on the outside when I loaded them in the boiler (out of desperation!), they burned incredibly well. So, yes the key is seasoned wood, and it's almost counterproductive to try with anything else. I will have plenty of seasoned wood for next year.

Having no storage is not a problem in this house. Rarely does my boiler capacity outrun the house's ability to soak up the btu's. I mean, if I'm willing to tolerate a 2nd floor at 76 degrees, I can almost always burn a full load of wood without the boiler shutting the fan down. Given my wood crisis/shortage this winter, I've not even tried storing any heat in the basement slab since Christmas. I've barely kept up the heat in the house at times... mainly due to bad wood.

The flue needs to be cleaned out mid season. A few weeks ago, my boiler pretty much quit working - wouldn't draw worth a crap. I removed the stove pipe and found it 90% restricted by ash that had made it's way into the flue. Now I'm back on these forums reading today and discovering that others have had the same experience.

Very happy with the boiler. Very happy with the radiant heat. If I had one thing to do differently, I would have bought the bigger boiler sizer, but I keep telling myself I still wouldn't have burned any less wood! Because our house is still unfinished (no basement ceilings!), we're heating 2200 feet of basement... one wall has two garage doors... and next winter that is going to not be the case!

-Thomas

 

[Hankovitch]

Hello Tom,
Interesting real-world experience you describe with unseasoned (not dry, aka 'wet') wood.
First, I am wondering...is the Tarm you are using is a gassifier? If yes, you should be burning the creosote in the secondary burn chamber, and you should not have what you describe as the soot (creosote?) buildup in your chimney nearly plugging it. If that is the case it argues VERY strongly about not burning wet wood....as I imagine there may have been sufficient water vapor with the creosote to preclude efficient burning in the secondary chamber, much of the creosote made it to the chimney where it condensed on the inside, dried out, and caused the 90% wood burner creosotic plaque. I'd call Tarm and ask them.
Now something additional on burning wet wood.
I posted this about a year ago on another thread, thought it would fit well here...
When purchasing wood for burning you needn’t ask if it is dry (the seller will always tell you it is dry!). Just look at the ends of the wood pieces where the chain saw cut through the tree. If you see what appear to be a number of slits, cracks or gaps where the wood fibers have separated, then it is at least somewhat dry. If the wood appears to be tight (no slits, gaps or cracks), then the wood is NOT dry, and you will use a lot of energy just to drive off the water before you can burn the ‘wood’.
Late this Spring or early Summer cut some wood of your own, split it, weigh it immediately, and record the weight on the ends of several pieces. Dry it for a while - 1 week, 3 weeks, 2 months, 4 months - and record the weight of the pieces through the Summer. It will be an interesting and revealing experiment. Let's look at a cord of wood (4'x4'x8'= 1 cord).
Let us assume the cord of wood you purchased is wet enough that it still has 400 pounds of water in it. (probably a VERY conservative number for an entire cord of freshly cut wood….freshly cut wood can be up to 80% water, and ‘seasoned’ or ‘dry’ wood will typically still contain 15-20% water).
See the link (broken link removed)
(Note: this link has information confirming that burning wet wood can be a cause of creosote buildup in chimneys)
Thought I’d try a fun calculation here to determine how much energy you will use just to drive off the water, and thereafter allow the wood to burn..
To heat water requires 1 BTU per degree per pound of water. Thus to heat one pound of water in the wood from 32 degrees F to 212 degrees F (to the temperature where the water can begin to boil away) will require 180 BTU per pound of water.
This means that you will use 72,000 BTU for the 400 pounds of water in the wood just to get the water to 212 degrees F.
But the water is still there, as a liquid - it is just a liquid at 212 degrees F!..........so read on.........
To convert 1 pound of liquid water at 212 degrees F to one pound of steam at 212 degrees F (where it will then have all 'boiled away') will require 970.4 BTU per pound of water….really.
For the 400 pounds of water, you will need to use 388,000 BTU to complete driving off the water.
Or, starting at 32 degrees F, for a cord of wood which still has 400 pounds of water in it, you will utilize 72,000 BTU + 388,000 BTU = 460,000 BTU jsut to drive off the water.....now you can use the BTUs in the wood to heat your home. This is 460,000 BTU which is NOT available to heat your home!............this is why it is best to dry the wood.

Also, you can purchase a unit to test the moisture content of the wood you purchase, (or the wood you cut and are drying) if you want to get high-tech.
See the below link…...and there are many other sources.
(broken link removed to http://www.drillspot.com/products/437287/Extech_MO210_Digital_Moisture_Meter)

Personally, I purchase scrap pallet wood. It runs about $12.00 per cord. Yes, it has nails in it, but I now just shovel them out from my OWB....and get paid by the ton to recycle them in the Spring at a local metal recycling facility. In my Garn (to be up and running for the 2010/2011 heating season in our Barn/Home) I will simply remove the nails with a magnet on a pole. One reason for burning pallet wood --- it is kiln-dried, and as such has a moisture content around 6-10%!! With the kiln-dried wood I waste very little of the BTUs in the wood to 'drive off water'.

Sincerely,

Hankovitch in SW Wisconsin