Wood Split Size for Froeling FHG boiler?

[DBoon]

I'm purchasing a house that will undergo a major remodel in all aspects - heating system included. The setup is ideal for a wood boiler (I've been lurking in the Boiler Room for some time, and I appreciate all the advice provided here over the years).

The likely choice is a Froeling FHG with lambda controls (20 or 30 kW size). Since many will likely ask me why I'm focusing on this particular boiler, I'll just say that it seems the most appropriate for use by the wife as well as myself.

I have several years of 16" cut wood for my wood stove, and I don't need to cut more to that length as I will likely be transitioning to the boiler in ~2 to 3 years. Therefore, I'm starting to cut and stack 20" length in anticipation of demand 2-3 years down the road.

My question is "what is the best split size or mix of sizes for the Froeling FHG boilers in a size of 20 or 30 kW?" Any thoughts and ideas are appreciated.

 

[kopeck]

Smaller seems to be better for a few reasons.

First is you can fit a lot more in your firebox when you are working with smaller splits. The other is smaller splits tend to season better, which is always good.

You will also hear about bridging. The firebox in my Tarm is very similar to that of a Froling and I really haven't had a problem with bridging except for this last week. I've been burning a bunch of funny sized small chunks and twice it's given me problems. I have two seasons of running my Tarm under my belt and with decent splits it's never been a problem in the past.

All that being said I don't get to picky. If I have larger chunks I put them on top. It all burns!

K

 

[hiker88]

I've burned everything from 16"-20" in length. Size wise, I burn everything from 2-3" rounds, and splits between 4"-6" or so and even a few bigger than that sometimes. I would say 4" or so is where your sweet spot is - not so much for burning, but pieces of that size fit together real nice and are easier to work with. I even burn real gnarly, knotty end pieces etc. and the unit will just eat them up. I think size is part of the equation, but I think moisture content is more important.

I've heard people talking about "bridging" but I've never experienced it. When the Froling is +-2c of the boiler setpoint, the fan is running at 85% and the fan is rated at about 540 cfm. That's a lot of air moving through the boiler. No matter what size pieces of wood I've loaded the boiler with, I've never found more than coals at the start of the next burn.

If you do burn really gnarly pieces of wood you may get a false positive alert on one of the safety messages, but Tarm NH walked me through changing the timer setting from the factory default to the recommended setting.

 

[jebatty]

All good advice by others. I suggest length 2" less than firebox size. That makes for easy loading and if a few pieces end up a bit too long, they still will fit just fine. My Tarm says 20" firebox, but 18" works so much better.

 

[maple1]

Different boilers operate a bit differently, but in my experience with mine - the more smaller splits you have loaded in there at a time, the bigger chance of producing more gasses all at once than can be efficiently burned (a common symptom = 'puffing'). I find a third to half load of small stuff to get things going good, followed by a full loading of whatever I can pile in there a half hour later works best for me. So I wouldn't spend a lot of time splitting everything real fine.

Main thing is to get a split surface on everything so it will season better - I just resplit at burning time as needed. An electric splitter in the basment comes in pretty handy.

 

[hiker88]

Different boilers operate a bit differently, but in my experience with mine - the more smaller splits you have loaded in there at a time, the bigger chance of producing more gasses all at once than can be efficiently burned (a common symptom = 'puffing').

Since the OP is asking about the Froling 20\30 I just want to let him know that "puffing" is another phenomenon I've never experienced with the unit. The unit will limit flu gas temps to 250c by closing the primary intake and slowing down the fan. I've experienced this on two occasions. I had one windy, gusty night and it was about 10 below. The other time was when I bought my wood splitter and I busted up the pine pallet it came on and filled the entire primary chamber with the 1-2 inch slats and pieces that were quite small.

With the pallet, I had a quick surge in flu gas temps and very low residual oxygen content. So the fan was running around at a lower power setting for awhile, the primary was closing, and the secondary went to 99% open real quick.

So, I agree with Maple that it isn't worth the time to split things too small, but it's more of a convenience thing than a concern about puffing.

Just saying

 

[DBoon]

Hello all, thanks a bunch for the advice thus far - this helps a lot. So far, my cutting and splitting strategy isn't too different from what you've all outlined - a mix of splits with an average size of 4-6" on a side with some smaller (to go on the bottom to get gasification going quickly) and larger allowable when they are the gnarly stumps or crotch pieces (i.e. don't sweat it when they are larger, but don't aim for that either). This is not so different than my wood stove, except that I can go to a larger overall size with the larger firebox. In general, I don't want to have really large pieces of wood because they will be too heavy for my wife to load into the boiler, and she is willing and able to load provided that 1) the splits are brought to the basement next to the stove, 2) they aren't too heavy, and 3) (implied) she doesn't have to get a master's degree in how to run a stove or boiler (hence the Froeling preference).

I hear jebatty's feedback on length - I cut my own wood, I use a tape measure to ensure a specified length, and mark the logs with chalk where they need to be cut. I also keep my chain evenly sharpened so I don't have issues with "diagonal" cuts and splits being longer than they should be. I had a "length" problem with my woodstove when I bought my wood and the guy who cut, split and delivered it for me never seemed to understand that 16" was the length I needed (no longer), and I was always using a chopsaw to get longer pieces down to size.

I understand the need to split to dry, so I don't keep big rounds. In my wood stove, I'll burn 4" rounds, but I let those dry a long time - much longer than the splits - and they work ok. In the beginning, I split big to dry and then split it smaller when I needed it, but now I am in the mode of splitting it once and being done with it. Being three years ahead (or more) makes it easier to be in that mode.

hiker88 - your boiler system seems pretty close to what I am aiming for. How does the 800 gallon storage work out for you? I also am planning on an unpressurized tank of ~ this size. That size storage seems to be pretty well matched to the Froeling 20/30 boiler firebox size given that I will be able to get usable heat down to 110 or 120 degrees F (or even lower depending on the season). Also, is the Froeling firebox depth 21" or does it fit a 21" piece of wood?

 

[hiker88]

hiker88 - your boiler system seems pretty close to what I am aiming for. How does the 800 gallon storage work out for you? I also am planning on an unpressurized tank of ~ this size. That size storage seems to be pretty well matched to the Froeling 20/30 boiler firebox size given that I will be able to get usable heat down to 110 or 120 degrees F (or even lower depending on the season). Also, is the Froeling firebox depth 21" or does it fit a 21" piece of wood?

800 gallons works well for me. I don't have an edpm liner so I heat it up pretty hot; at least 85c or so every burn. The amount is good; we had a fairly cold winter this year and I got by on one fire a day and kept the house at 70f.

I just looked at my owners manual and max firewood is specified at 21 inches. I measured what I'm burning lately and I found some pieces that are 20.5 inches and I've not had any issues with pieces not fitting obviously. I know I've burned longer stuff before though because I just put it in at an angle, but that doesn't happen too often. I think I marked my chainsaw bar at 19" to give me some fudge factor and most of my pieces seem to be around there.

The refractory has a lip on the front that funnels wood bits towards the center of the firebox and the nozzle, so when you put a long piece of firewood along the bottom you will have a gap between the bottom of the firewood and the top of the refractory. Once you get up about an inch or so, you have the full depth of the firebox. However, I follow Tarm's advice on keeping a good bit of ash etc. in the primary chamber so that fills any gaps between the refractory and the first pieces of firewood you put in to start a fire, and once you get a fire going, all the coals just fall down around there any way. I don't use any kindling to get fires going. I take wood out of my bunker, put it in my weight scale and then whatever is on top of the pile goes in the firebox first.

I'm burning right now, but I will measure the firebox for you later.

 

[flyingcow]

FWIW, I have the Innova. 21.5 inch box. Maybe a bit less. I cut 20 inch wood, works well. Occasionally i have a few long ones. I put those on top. I try to keep my size of splits to 4x4 to 6x6. But as someone else stated, the bigger ones go on top.

welcome to the gasser world. Also, the Tarm customer service has been good. Which for the price, should be.

 

[arngnick]

I don't want to have really large pieces of wood because they will be too heavy for my wife to load into the boiler, and she is willing and able to load provided that 1) the splits are brought to the basement next to the stove, 2) they aren't too heavy, and 3) (implied) she doesn't have to get a master's degree in how to run a stove or boiler (hence the Froeling preference).

Just a thought but my wife has NO issues operating our boiler...she is actually really happy with it. You are probly a couple hours from me so if you would be interested in seeing how a Varm operates I would be glad to show you. Although I have a natural draft unit the vedloux 37 has induced draft and is even easier to light. We light a few small splits with a torch throw a small piece of cardboard on top then finish loading the firebox. The loading unit starts once the fluegas temp reaches its setpoint and continues to burn until it is out. The only "thinking that is required is to make sure your storage can accept the heat that the load of wood will generate. We have not have any issues with over heating though.

My manual says splits that are 3"-6" are ideal. I have loaded larger wood without issues too. Mose recently I have been buring wood that is a little on the higher side of the moisture content without any problems at all.

[Edit] Varm also makes some really nice Lambda boilers. They operate the much like mine. Check them out at (broken link removed)

 

[skfire]

Firstly congtats on the choice and good luck with the installation..do it right once...take your time.

In my FGL, the first year I burned what I had, which was a crazy mix of all sizes and lengths.
Some I had to re split, but generally I noticed it does better with 4" as an average.
Regardless, it did fine with all the sizes I did have.
The ones that were more problematic were the short fat uglies..which I used as end of year or shoulder season burns..and the hemlock ones gave some grief, I had a shut down with them..the pieces were just too odd shaped and made a lot of gaping, not too mention the hemlock was dry and light. But that was my fault..trying to burn what I would normally save for the firepit. Next hemlock batch, re-split more to size burnt great, especially with a piece or 2 of oak on top..
Now I tend to put the odd ball pieces on the top of the stack, especially ones with turns and bends and limbs sticking out..

Second year I ran mostly ash cut to 19"-20" lengths and ranging form 3-6" in thickness. Great results. Too easy..
I would stay away from too many 21" long pieces. They may hang up on front inside of the firebox.

Pack them tight(avoid wedging pieces facing upwards) but loose on the sides of the boiler and bridging is a non issue. Make sure you have a good bed of ash...couple of reasons for that, but one of them being the lip issue that others mentioned.

Above all DRY DRY DRY..even though I did burn some larger 20%mc pieces with no issues, noticed though the efficiency and secondary burns were somewhat down. Normal mc range currently is between 10% and 16%

Feel free to pick our brains regarding this boiler.

Scott

 

[Chris Hoskin]

We would tend to recommend 18" firewood length, but I am glad to hear that others are having good success with longer pieces.

 

[kopeck]

I never addressed length in my post but I cut ever thing 16".

It's just what we're setup for, It's not worth the pain to do some 18" (which would be ideal) and some 16" for my stove and my fathers setup.

K

 

[skfire]

We would tend to recommend 18" firewood length, but I am glad to hear that others are having good success with longer pieces.

Currently cutting 19", but some stragglers go 18" or 20",
like I said 21" may be cause hang ups..if I have them I throw them on top slightly diagonal.
Either way the boiler works admirably.
See some attached pix of stacks.

Scott

 

[DBoon]

Hello hiker88 and skfire, thanks for the Frohling feedback - that gives me reassurance on what to plan for. Also good advice from Chris Hoskins, flyingcow, jebatty, and maple1 - different boilers but there is much for me to learn - thanks.

Hello kopeck, I too have a wood stove today that requires 16" splits. If I keep this and move it to the new house, I'll have plenty of 16" wood to feed it for many more years on a part-time basis. I am definitely looking forward to less cutting and splitting with longer lengths.

Hello arngnick, I won't rule out a different lambda-controlled boiler, but I will definitely get a lambda-controlled unit. I've watched my wife operate the woodstove long enough to know that she is not that interested in optimizing burns by adjusting controls, or even getting the burn right at all. Anything more than load, light and walk away is not going to be successful, and I want it to work for both of us. So the extra $$ is worth it here in my case.

 

[arngnick]

Hello hiker88 and skfire, thanks for the Frohling feedback - that gives me reassurance on what to plan for. Also good advice from Chris Hoskins, flyingcow, jebatty, and maple1 - different boilers but there is much for me to learn - thanks.

Hello kopeck, I too have a wood stove today that requires 16" splits. If I keep this and move it to the new house, I'll have plenty of 16" wood to feed it for many more years on a part-time basis. I am definitely looking forward to less cutting and splitting with longer lengths.

Hello arngnick, I won't rule out a different lambda-controlled boiler, but I will definitely get a lambda-controlled unit. I've watched my wife operate the woodstove long enough to know that she is not that interested in optimizing burns by adjusting controls, or even getting the burn right at all. Anything more than load, light and walk away is not going to be successful, and I want it to work for both of us. So the extra $$ is worth it here in my case.

Not saying that a Lambda unit is not super cool and effective because they are. I went with the boiler I did because the lambda boilers are almost intimidating to some wives. They have so many controls and electronics (not thaty they will be messing with them). I will step out on a limb and say the boiler I have may be the simplest on the market. It has 1 air adjustment and I have never messed with it since I set it. The only thing you do to operate it is light it and load it. If you see a flame in the bottom IT WILL BURN so walk away. My lightings take 5-10 min. There is not even a button to push to start the boiler since everything is natural draft. Once the boiler comes up to temp the loading valve does it thing. VERY SIMPLE and effective!

In some aspects I would LOVE a lambda unit, but I am very pleased with my boiler in many ways and since it works so well and there are no electronics or motors to maintain the boiler is essentially maintenance free plus I saved about 5K compared to a lambda unit. Of course all the heating components will require maintenance.

My offer stands if you would like to see my boiler in operation or I can even take a video (I think). If you are interested of course. I think you are on the right track and will be happy no matter what direction you take!

 

[JP11]

You're not far from Mark at AHONA. I think he's got a couple different setups at his shop. Go and try them. He'll let your wife play with the buttons I'm sure. After a few weeks of grumbling from my wife, she now won't let it kick over to oil.

JP

 

[maple1]

+1 on arngnick's last post (naturally ) .

There is nothing simpler than these natural draft units. No controls or electric stuff at all - except for the circ pump, of course. I also think the natural draft provides a 'pseudo' self-regulating burn control not available to mechanically forced/induced draft units - unless you step up to Lambda. As the fire gets going the chimney draft builds itself up (akin to a fan speeding up), as it dies out at end of a burn the chimney draft decreases (akin to a fan slowing down). So you start with no or very little draft/air intake before you make a fire, go all through your burn with rising then falling draft/air intake, then when the fire goes out there is no or very little draft/air intake again. All without any electric fans or related controls. Sort of like a turbo charger - with a barometric damper as the wastegate.

If I didn't have this tall chimney (a requirement for natural draft), I would likely look seriously at lambda.

 

[DBoon]

I appreciate everyone's insights into natural draft versus forced air and lambda vs. non-lambda. The simple reality is that if it were for me alone, I would choose simplicity over complexity (and save the money) and wouldn't mind dialing it in manually, when needed. I do this on my stove all the time. The simple reality is also that my wife hasn't done this on the stove, doesn't show any inclination to start doing that, and despite my repeated efforts at helping her to understand how to use the stove correctly and run it more efficiently, she will not change.

So, the likely outcome of purchasing something that is not lambda-controlled and pretty much hands-free is either 1) an inefficient, smokier burn, or 2) failure to use it if I am not around, at which point all of the money I saved is a moot point.

When I asked my wife 1) do you like the ambience of having a wood stove or 2) do you like the heat? Her answer was "the heat". That tells me everything I need to know

 

[JP11]

lambda makes it easy on the ones who don't CARE how it works, or what an efficient burn even is.

Push button
Load wood
Push button.

Done deal.

 

[arngnick]

lambda makes it easy on the ones who don't CARE how it works, or what an efficient burn even is.

Push button
Load wood
Push button.

Done deal.

Not to push the issue... But mine works the same way! As Maple said self regulating...

Load wood
Light Fire

DONE DEAL!

 

[mikefrommaine]

You're not far from Mark at AHONA.

Ah, man I didn't know this was a Lambda/push my brand of boiler thread. Hope I'm not too late:

Buy a Biomass It's the BMW of boilers.

 

[JP11]

I was trying to be helpful to the man to LOOK at a boiler in operation.

Never did like those BMWs.. except the bikes. I've had a couple of mercedes though.

JP

 

[DBoon]

Thanks for all of the additional suggestions on lambda-controlled boilers. I'll be sure to do a more exhaustive search as the time to purchase grows closer.

 

[hiker88]

Welcome to our dysfunctional family.