Gasification Boilers--Things to consider?

[Rusnakes]

Greetings everyone,

We recently became acquainted with outdoor wood gasification boilers in a search of options to retrofit our 1830s (renovated/insulated) home. We originally were going to add a wood stove to the house (a Jotul F55, which was already purchased), but due to a series of changes in plans, we ended up not installing the wood stove (we anticipated a move, decided to take the wood stove with us for a new build project, finished up the renovation of the current house before the move, ended up not relocating). Current house is about 2500 square feet. The house is circled with trees, but there is open space closer to the house and along the back of the garage. We can also remove trees if needed.

So, we'd still like to get the benefit of a wood stove, but shifted our attention to retrofitting the house with an outdoor wood gasification boiler. We currently run our high efficiency furnace on propane and supplement with electric heaters in the immediate space (mostly kitchen) to keep the main furnace off during the day. Propane heat is just a money pit, imho. Our new build was supposed to be off-grid (or nearly off grid), so we are looking at options here at our current home to streamline what we do energy-wise. Our current water heater is electric as well.

After spending a lot of time learning about wood stoves, we are back to step one with gasification boilers. I would be curious to know what recommendations folks have for an outdoor boiler, as well as any other things to consider in a retrofit project. We would like to have a storage tank in the basement (something we were already considering for a solar water heating system on the new build project) and would like to utilize our current furnace/ductwork to transfer heat in the house. We'd love to do radiant floor heat, but we have wood floors throughout the first floor of the house and from what I read, that is not recommended (and we have a couple of spots in the house where it would be nearly impossible to get radiant heat into without tearing out the flooring, due to the design of the foundation/add-on sections over the years).

Any thoughts or suggestions would be great. Many thanks.

 

[velvetfoot]

An outdoor wood boiler and piping would be quite expensive and still use a lot of wood because of heat loss, I feel. Propane is cheap now, isn't it? A stand alone wood stove can operate without a fan for off grid/power failure, but more effective w/blower, and would use a lot less wood than an outdoor unit, I'd say. Can you get a bigger stove and still use the same chimney?

Can you maybe make the propane system more efficient, like adding zones?

 

[maple1]

An indoor boiler is out of the question?

 

[Rusnakes]

An outdoor wood boiler and piping would be quite expensive and still use a lot of wood because of heat loss, I feel. Propane is cheap now, isn't it? A stand alone wood stove can operate without a fan for off grid/power failure, but more effective w/blower, and would use a lot less wood than an outdoor unit, I'd say. Can you get a bigger stove and still use the same chimney?

Can you maybe make the propane system more efficient, like adding zones?

Interesting. I was under the impression that outdoor wood boilers were roughly as efficient as the indoor varieties, if you insulate the piping. Propane is not cheap and it varies from season to season. We don't use enough to get on local pre-buy plans, so we fluctuate with the prices. It was $2.89/gallon last fill up. In a conservative year, we will still probably use about 1000 or so gallons of propane.

We basically zone the house right now for daytime and nighttime usage, so our relative run-times for the furnace are quite minimal, all things considered. We keep indoor temps between 60 and 63 most of the winter as well. We are in Michigan, so "winter" temps are here for a minimum of 6 months.

We don't have an indoor stove nor chimney at this point, as the home did not have one and we did not rough one in with the renovations (thinking we were moving, so why bother). So, we thought an outdoor boiler would serve roughly the same purpose, and the gasification boilers are more efficient than standard boilers and produce less smoke when run correctly. So, basically, we are trying to get out from under the propane cycle, plus have a reliable off-grid source for heat and hot water.

 

[Rusnakes]

An indoor boiler is out of the question?

Honestly, we hadn't really considered an indoor boiler, to be honest. We do have a basement (about 700 sqft, which includes long-term food storage, the furnace, and odds and ends) with an exterior (Bilco) cellar doorway. First big questions I have--What are wood storage issues with an indoor boiler? And how much does it raise your home owners insurance rates?

Thanks for the suggestion. We have only been focused on an outdoor boiler up until now.

 

[Rusnakes]

Oh yes...just waking up!! What type of chimney requirements do you have with an indoor boiler? Standard as with a wood stove? If so, that would be an issue for us since we have completed the renovations on the house (interior and exterior) and would require quite the retrofit at this point(especially through the new roof, etc.). Our original plan for a wood stove was really difficult for siting in the house because of an excessive number of windows and doors (with a typical number of ducts as well). So, that was another reason for shying away originally from anything indoor and considering an outdoor boiler.

Honestly, we hadn't really considered an indoor boiler, to be honest. We do have a basement (about 700 sqft, which includes long-term food storage, the furnace, and odds and ends) with an exterior (Bilco) cellar doorway. First big questions I have--What are wood storage issues with an indoor boiler? And how much does it raise your home owners insurance rates?

Thanks for the suggestion. We have only been focused on an outdoor boiler up until now.

 

[maple1]

Mine had no effect on my insurance - but you should ask your insurance agent about that. What he says may factor big in a decision. Ask him about OWBs too.

Wood storage issues are dependant on your setup. I have a walkout basement with a roll-up door, and wheel all my wood in. The whole winters wood is in there before winter comes.

Outdoor units are less efficient than indoor. No matter the boiler, there will be standby losses from it. If the boiler is inside, the losses will be to the heated space. And should be less, since the dT outside will create more heat loss. Also, good underground piping is in the $15/ft range to buy. May or may not be a factor for you - but should be considered. And you don't want to use stuff that is not good.

All kinds of considerations - it might get decided that an OWB is the fit for your situation. Just that you should be sure to consider everything you can think to consider before deciding.

 

[Rusnakes]

Absolutely. We plan to think this through for many, many months. We mulled over the indoor wood stove for the better part of 3 years, so we don't move very quickly on any decision, without knowing every in and out we can.

Mine had no effect on my insurance - but you should ask your insurance agent about that. What he says may factor big in a decision. Ask him about OWBs too.

Wood storage issues are dependant on your setup. I have a walkout basement with a roll-up door, and wheel all my wood in. The whole winters wood is in there before winter comes.

Outdoor units are less efficient than indoor. No matter the boiler, there will be standby losses from it. If the boiler is inside, the losses will be to the heated space. And should be less, since the dT outside will create more heat loss. Also, good underground piping is in the $15/ft range to buy. May or may not be a factor for you - but should be considered. And you don't want to use stuff that is not good.

All kinds of considerations - it might get decided that an OWB is the fit for your situation. Just that you should be sure to consider everything you can think to consider before deciding.

 

[velvetfoot]

2 story house? Did the place used to have a chimney? You already have the stove-you'd need to put in a chimney. It'd be nice and cozy near the stove and beyond-no more 63. Plus good off grid. For an outside boiler you'd need a generator to power the pumps and distribution fan.

 

[grader]

you could also build a small shed (8x12) close to the house and put an indoor gasification boiler in it. minimal cost for pipe, wood and mess outside, check with insurance and local codes first. also remember that the wood is going to be near it when choosing a location.

 

[velvetfoot]

Around here they have rules on distance to house, distance to property line, height of stack, so you may wind up with an installation with a high stack and not so close to the house. But, it is probably safer...a chimney fire won't take out the house.

 

[stee6043]

Aside from the type or location of the boiler you may end up with have you considered how you'll feed this beast? 2,000gallons of propane is a very healthy appetite for fuel if you are indeed turning your propane furnace off at certain times throughout the day. If I had to wager a guess you're going to be in the 10+ cord of wood range, minimum. That is a LOT of wood to manage for the average homeowner with other things to do "most days".

Had you not just completed your renovations I would have recommend you invest heavily in insulation. Making your house super-insulated would have been a far better investment than wood heat on the front-end.

Have you considered pellet? You can put a pellet stove or boiler inside and direct vent through a wall (no chimney). It should be cheaper than propane if you buy un bulk but will not be as cost effective as wood depending on how much you value your time...

My two cents only.

 

[velvetfoot]

I thought he said 1000 gal/yr.

 

[Rusnakes]

Yes, we are at 1000 gallons/year, give or take. And, we did reinsulate the entire house from the exterior (R-13 regular fiberglass batts at first, then transitioned to R-15 Roxul batts the remaining walls of the house. Ceilings are at R-50 in one cathedral ceiling, then R-60-70 in the rest of the house). So, short of spray foam, it is as well-insulated as this ole farmhouse can get. We homestead, so it wouldn't be terrible to deal with wood (but I also don't want to turn my life over to it either! ).

The indoor boiler in a separate building might be a good intermediary solution. Insurance would be something to check out (I have no idea how they view outdoor boilers at all), but we have very limited local requirements for most everything in our township. We typically ask to do X and they say "sure". That said, we would want something very safe and sited well, so there are a lot of considerations there. I don't know of anyone locally doing what we are considering, so searching online (and here) will likely be the bulk of our research.

I considered pellet at one point, but wondered if it wouldn't be better to just consider wood, if it could be done. I will definitely read up on the pellet stoves to learn more. I simply don't have enough background knowledge in that area to comment.

 

[92rslt1]

Hello my friends. I have both an indoor gas boiler and a outdoor gasification boiler. Both work extremely well but both have cons. The indoor gas unit is nice because it is automatic. Comes on when I need it and requires very little to keep it going. Thats the beauty of LP I suppose. The downside is running it for 8 months will eat about 3-4k worth of lp. So it is used as an automatic back up and for fall or spring.

My gassifier is a Central boiler 1400. My house is post 96 building code, so its rather well insulated, but the mice ran off with some, so it does get drafty in certain spots. The outdoor boiler is a pain at times, I'm not gonna lie, and cleaning up the mess from the wood processing is even worse. There so much work in splitting, stacking and drying it almost makes me want to just pay for the fuel. Unfortunately money isn't free, so that's where I exchange sweat for heat.

The CB works amazing though.. that's what makes it all worth it. I made the classic mistake of running undersized lines and estimate my btu from the outdoor boiler to be around 100k @ max after over sizing the pump. That being said my house in the frigid upstate NY is an easy 75* on the coldest winter days. There certainly is no concern that I am going to be cold. My rooms are zone controlled, my floors are heated too and I have no regret when I am warm that I had to split and stack wood all summer.

The key to a happy gassifier is DRY wood. I can't stress that enough. I run wet wood in mine at times and it waste twice as much and clogs up the air ports
.
I would recommended a gassification boiler to anyone, and as long as they understand its not an incinerator, its a gasification boiler they will be very happy.

Some details...
2009 CB1400
During fall I load it once a day before bed.. house is 70-75 (It gets the house ridiculously warm when the wife gets carried away with the thermostats.)
coldest months about every 12-18 hours.. house still 70-75
12 cords a year of mixed wet/dry hard wood. Less with dry, probably 10 cord.
heats 3400ft 2 story + basement (just from heat escaping the plumbing.)

Hope this info helps.

 

[Rusnakes]

Thanks very much for the input, 92rslt1. That is quite helpful. We are probably just a smidge warmer here than where you are in upstate NY, so that info helps a lot.

I'm curious how far your unit is from your home. And, if you had the opportunity to do it all over again, would you "right size" or oversize the line. As for wood, since we have no ready supply of hardwoods (only a neverending supply of softwoods), we'd have to purchase wood locally. But, last I looked, face cords of wood locally were $60-75 delivered (around $80-100 delivered and stacked), so even 15 face cords would be a huge savings to us.

Do you run your hot water off of the system as well, or just heat?

Hello my friends. I have both an indoor gas boiler and a outdoor gasification boiler. Both work extremely well but both have cons. The indoor gas unit is nice because it is automatic. Comes on when I need it and requires very little to keep it going. Thats the beauty of LP I suppose. The downside is running it for 8 months will eat about 3-4k worth of lp. So it is used as an automatic back up and for fall or spring.

My gassifier is a Central boiler 1400. My house is post 96 building code, so its rather well insulated, but the mice ran off with some, so it does get drafty in certain spots. The outdoor boiler is a pain at times, I'm not gonna lie, and cleaning up the mess from the wood processing is even worse. There so much work in splitting, stacking and drying it almost makes me want to just pay for the fuel. Unfortunately money isn't free, so that's where I exchange sweat for heat.

The CB works amazing though.. that's what makes it all worth it. I made the classic mistake of running undersized lines and estimate my btu from the outdoor boiler to be around 100k @ max after over sizing the pump. That being said my house in the frigid upstate NY is an easy 75* on the coldest winter days. There certainly is no concern that I am going to be cold. My rooms are zone controlled, my floors are heated too and I have no regret when I am warm that I had to split and stack wood all summer.

The key to a happy gassifier is DRY wood. I can't stress that enough. I run wet wood in mine at times and it waste twice as much and clogs up the air ports
.
I would recommended a gassification boiler to anyone, and as long as they understand its not an incinerator, its a gasification boiler they will be very happy.

Some details...
2009 CB1400
During fall I load it once a day before bed.. house is 70-75 (It gets the house ridiculously warm when the wife gets carried away with the thermostats.)
coldest months about every 12-18 hours.. house still 70-75
12 cords a year of mixed wet/dry hard wood. Less with dry, probably 10 cord.
heats 3400ft 2 story + basement (just from heat escaping the plumbing.)

Hope this info helps.

 

[92rslt1]

Yes, indeed. My biggest regret is not running the proper lines. If I could do it all over, I would run two spans of 1 1/4 thermopex. While technically it works great without it, I would like to heat my garage now as well and I just wont be able to pull the BTU I need off the lines I have.

My unit is about 40 feet or so of thermopex before it comes out of the ground and reaches the house. From there it runs another 70 through the crawlspaces into the basement boiler room. Its all insulated, so approximately 120ft each way. It heats both the house and the hotwater heater. Its setup hot water on demand, with a side arm as well.

How much are full cords locally? They are about 150-170 here. I burn about 12 full cord.

 

[Rusnakes]

10 full cords of wood?? Wow, that's a lot. The typical measure of wood around here are face cords (I have no idea why they prefer that...probably shorter pieces of wood is my guess). Full cords are available--about $175 delivered (not stacked). I'm glad you clarified that. I assumed you were talking face cords!

Thanks for the info on feel from the house. That would be about what I would expect for an external run (but a lot shorter on the interior b/c I would bet it would enter by the utility and only have about 8 or so feet on the interior to the furnace area).

Do you find you waste a lot of heat (i.e., unused heat potential) and have you considered a storage tank inside?

Yes, indeed. My biggest regret is not running the proper lines. If I could do it all over, I would run two spans of 1 1/4 thermopex. While technically it works great without it, I would like to heat my garage now as well and I just wont be able to pull the BTU I need off the lines I have.

My unit is about 40 feet or so of thermopex before it comes out of the ground and reaches the house. From there it runs another 70 through the crawlspaces into the basement boiler room. Its all insulated, so approximately 120ft each way. It heats both the house and the hotwater heater. Its setup hot water on demand, with a side arm as well.

How much are full cords locally? They are about 150-170 here. I burn about 12 full cord.

 

[92rslt1]

As far as waste, I believe the largest waste is cranking the heat up too far. Once the temp has been reached on the gasser it shuts down and sleeps. So usually the only time it's really eating a good amount of wood is when it's calling for heat for extended periods of time. As far as storage goes, I have never really considered it, just for the simple fact it works so well without it. It's heats up from a cold start quickly and maintains temp as needed. I might add storage eventually since the general consensus is that it does help.

 

[dogwood]

Rusnakes, if you do have basement space for an indoor gassifier you'd be utilizing all the excess heat coming off the boiler and piping. You'd be surprised how much excess heat that is, even with well insulated piping. Our indoor gassifier is located in an unheated room partitioned off from the garage, due to our not having a basement. It seems it's always at least 90 degrees out in the boiler room even in the dead of winter, plus there's standby heat loss from our insulated 1000 gallons of storage out in the garage proper. That's heat I wish we weren't sending to the great outdoors.

Our wood boiler installation was a retrofit too, like yours, so I fully appreciate what a pain finding a route for and installing double wall chimney pipe would be for you. It's a one time job however, unlike unnecessary splitting, stacking and burning to heat a back yard.

If you already have duct work and a forced hot air heat you can likely put a water to air heat exchanger over your furnace to utilize your current system. The bigger the hx the better. That's what we do. You might also look into the Kuuma line of gassifiers which may or may not fit your living situation. They heat and send hot air directly into your ductwork. No messing with water and plumbing. I think this would make for a much simpler and more economical installation. I'm not sure how often Kuuma's have to be loaded with wood each day or whether you or someone would be home to do that if need be. It may be worth checking into for you. People on site seem to have good things to say about them. Good luck.

Mike

 

[mike van]

Just a few indoor/outdoor things - We had in the basement Harmon non gasser no storage for 16 years. It would eat about 9 full cord a year. I have a standing record here in Kent for non reported / not responded chimney fires,despite every effort of mine to clean a chimney that would fill with that hard glassy almost bulletproof creosote. Throwing that much wood into the basement sucks, no nice way to put that . On the bitter cold nights, it would be out & the oil come on by 3 AM. I do miss the 'free' heat in the basement & the ability to gravity feed the system should the power go out, but thats about all. I threw the chimney brush away 4 years ago when I bought a Garn & put it in an addition on the garage.

The wood consumption went down to 7 cord, I move it now on half cord pallets with my old Trojan loader, set them right in that shed & toss the wood 3 ft into the Garn. I do have to buy a 5 to 6 kw generator yet, as if the power should go out, there's no way to move that 1000 gal. of water through the house boiler. It's a rare thing here, as we're on the main road. Just me, i'd never go back to the basement setup, the threat / chance of fire, moving the wood. The only fire now inside is the fireplace, not very efficient, but nice to watch.

 

[dogwood]

Mike, I appreciate your concern about chimney fires. Its one of the reasons I bought a gasser, which at least in it's first year hasn't created any noticeable creosote in the chimney lining. By the way, nice looking home you have there. I like how the extension to your garage looks. Is the space above the doors for ventilation? I've got to do something this Spring to house our tractor. Maybe a similar garage extension would do. Don't mean to get your thread off track Rusnakes.

Mike

 

[mike van]

Just a transom window I made to let some real light inside -

 

[Rusnakes]

Thanks for all the great ideas, Mike. I greatly appreciate all the input.

Rusnakes, if you do have basement space for an indoor gassifier you'd be utilizing all the excess heat coming off the boiler and piping. You'd be surprised how much excess heat that is, even with well insulated piping. Our indoor gassifier is located in an unheated room partitioned off from the garage, due to our not having a basement. It seems it's always at least 90 degrees out in the boiler room even in the dead of winter, plus there's standby heat loss from our insulated 1000 gallons of storage out in the garage proper. That's heat I wish we weren't sending to the great outdoors.

Our wood boiler installation was a retrofit too, like yours, so I fully appreciate what a pain finding a route for and installing double wall chimney pipe would be for you. It's a one time job however, unlike unnecessary splitting, stacking and burning to heat a back yard.

If you already have duct work and a forced hot air heat you can likely put a water to air heat exchanger over your furnace to utilize your current system. The bigger the hx the better. That's what we do. You might also look into the Kuuma line of gassifiers which may or may not fit your living situation. They heat and send hot air directly into your ductwork. No messing with water and plumbing. I think this would make for a much simpler and more economical installation. I'm not sure how often Kuuma's have to be loaded with wood each day or whether you or someone would be home to do that if need be. It may be worth checking into for you. People on site seem to have good things to say about them. Good luck.

Mike

 

[Rusnakes]

No worries! I like off topic discussions! And we were just discussing dogwood's building here as well. Well done. Very attractive. And I appreciate all the input about your situation (especially with the chimney fires!).

Mike, I appreciate your concern about chimney fires. Its one of the reasons I bought a gasser, which at least in it's first year hasn't created any noticeable creosote in the chimney lining. By the way, nice looking home you have there. I like how the extension to your garage looks. Is the space above the doors for ventilation? I've got to do something this Spring to house our tractor. Maybe a similar garage extension would do. Don't mean to get your thread off track Rusnakes.

Mike