Will a Garn Jr. work for my application?

[Golovkin]

Hello,

I am in the early phase of building a house, and learning about wood gasification boilers.

The house:

1280 sq/ft daylight basement with 1/2" pex through slab. Slab is on 2" foam board and footings are insulated.

1280 sq/ft Main floor with 70% hardwood and 30% tile (plan to go with proper staple up, due to cost of Warmboard...)

900 sq/ft loft (not sure if this needs a staple up zone? Seems it would always stay warm)

The house is not built yet, but I plan to insulate it as efficiently as possible - it won't be super insulated, but "good". There will be some large picture windows in one room and the main floor open to the loft causing a tall ceiling.

Picture a tall house with a 32' X 40' foot print

Attached garage 1,200 sq/ft - only needs to be kept above freezing

The Plan:

Garn Jr. with 33kw electric unit installed for back up (electric is cheap here). the unit would be placed in the attached garage and insulated very well.

Zone 1: Basement Circuit using low temp through concrete, 1/2" pex 1' centers
Zone 2: Main floor, higher temp 130-140f using staple up under hardwood floor, 2 runs/joist (insulated underneath)
Zone 3: Garage circuit, low temp through garage floor 1/2" pex 2' centers, this zone would be ran to keep the garage above freezing only.

The situation:

I own a tree care company that produces more wood than I can possibly burn. I also work 30 minutes from this house, so I don't want to feed a stove during the day. My hope is that I can burn once in the morning and once in the evening for most of the winter. On really cold days (-20f or less ) this might change to 3 times per day and the electric can pick up my slack. I'm not too concerned about the total amount of wood used - more the hassle of feeding and lighting fires all the time, and my wife/daughters feeling comfortable and complaining less

Also - the electric would have to keep the entire house above freezing during vacations.

The Question:

Is this unit feasible for what I'm trying to do? Are there better options? I understand there a thousand calculations and pieces of information that one might need, but what does real world experience tell you about a Garn Jr. working in an application like this?

 

[Hydronics]

I'd bet a 1000 would do the job well for you. You should do heat loss calcs to verify that you will have the stored btus you desire between burns. I'd recommend foam or sip's, money spent on insulation is definitely well spent, it can't really be overdone. Personally, I'm impressed with the Garn's simplicity and feel that it's a durable design.
I'LL bet heaterman will chime in with useful advice once he sees Garn in the title.

 

[bioman]

Bigger is always better !

 

[mike van]

How bitter is the cold in the part of Montana you're in ?

 

[heaterman]

Sounds like a nice place.

What you're going to need there is a 2 temperature system. The slabs will both do fine with water temps of 100* or less. Maybe as low as 80-85* especially in the basement where the heat loss will probably be less than 10btu/ sq ft.

The "fly in your soup" with that plan is the main level. It will require much higher water temp than the other two areas. That floor will probably need 150* water or higher to provide adequate heat output when you get down to design conditions outside.
This will limit the minimum temperature of any type of thermal storage you elect to use. Garn included. In practical terms this means you will have to maintain the thermal storage at a higher temp, which requires more frequent firing.

If it were mine, I'd do the underfloor tube like you have planned but either install, or leave provision to install, some additional heat on the main level. This could be some baseboard or panel radiators placed in strategic areas of the house where the heat coming from them could circulate freely. The additional output capability will allow you to heat with a lower overall water temperature. and give you more time between firing whatever you would use as your heat source.

I would highly recommend a heat loss calculation for the house so you know what you're dealing with there. From that you will be able to make an informed decision on basically everything to do with the project. Water temps, tube size, pump selection, tube spacing, how many btu's and where they are needed, etc etc.

And yes, A Garn Jr would be a no brainer for your application there.

BTW....what are your electric rates there and do you have "off peak" rates available?

 

[Woodfarmer1]

I can echo what heaterman said, my great room is 24x30 , 19' sidewall and 12/12 pitch.
The in-floor will not heat my space even tho I pump 150* water through it.
This summer I will be adding a few stelrads to my system.
The garn does a good job of creating hot water

 

[Golovkin]

Sounds like a nice place.

What you're going to need there is a 2 temperature system. The slabs will both do fine with water temps of 100* or less. Maybe as low as 80-85* especially in the basement where the heat loss will probably be less than 10btu/ sq ft.

The "fly in your soup" with that plan is the main level. It will require much higher water temp than the other two areas. That floor will probably need 150* water or higher to provide adequate heat output when you get down to design conditions outside.
This will limit the minimum temperature of any type of thermal storage you elect to use. Garn included. In practical terms this means you will have to maintain the thermal storage at a higher temp, which requires more frequent firing.

If it were mine, I'd do the underfloor tube like you have planned but either install, or leave provision to install, some additional heat on the main level. This could be some baseboard or panel radiators placed in strategic areas of the house where the heat coming from them could circulate freely. The additional output capability will allow you to heat with a lower overall water temperature. and give you more time between firing whatever you would use as your heat source.

I would highly recommend a heat loss calculation for the house so you know what you're dealing with there. From that you will be able to make an informed decision on basically everything to do with the project. Water temps, tube size, pump selection, tube spacing, how many btu's and where they are needed, etc etc.

And yes, A Garn Jr would be a no brainer for your application there.

BTW....what are your electric rates there and do you have "off peak" rates available?

Thanks guys! I really appreciate your thoughts and help. Up until a month ago I didn't know wood burning was anything more than feeding my old hurricane wood stove at all hours of the day.

So - I need to learn more about the homerun trv radiator layouts and do some heat calcs. I'll do this as the house plans get closer to completed.

Question: Can I run my main floor staple up at low temp like the radiators? I'm hoping I can take the chill off the floor, and the radiators will supply the bulk of the BTU to the big open rooms.

I live About 60 miles from the coldest recorded temp in the lower 48 (-70), it isn't always harsh in winter here, but it can hit -30 or -40 for a couple weeks some years. I understand during these times that I'll be tending a garn all day, but there really isn't anything else to do when it gets like that!

 

[heaterman]

Question: Can I run my main floor staple up at low temp like the radiators?

You can run your radiators and underfloor at the same temp. Now, what you mean by "low temp" needs to be nailed down before anyone can give an informed answer.
Normally you would want to run your rads between 130-180* depending on how you size them.
For best output from the floor, you'll want the water about as hot as you can get it.

 

[kjahnz]

1280 sq/ft Main floor with 70% hardwood and 30% tile (plan to go with proper staple up, due to cost of Warmboard...)

Warmboard?
not sure what that is? is it pex in lightweight jibcrete? Seems the simplest design you could do is pex in a jibcrete slab on this main floor.
you could then run all emmiters at the same temp. It is working fine for me.

 

[heaterman]

Warmboard?
not sure what that is? is it pex in lightweight jibcrete? Seems the simplest design you could do is pex in a jibcrete slab on this main floor.
you could then run all emmiters at the same temp. It is working fine for me.

THAT is the best way for comfort, economy of operation, and simplicity!
Probably no need for rads in this scenario.

How many times can I hit the "like" button.........?

 

[velvetfoot]

I'm no expert, but I searched on warmboard. For floors It seems like it's meant for under wood, which is an isulator . Can tile be put directly over the gypcrete? How about something in the ceiling; that way there'd be no resistance to heat in the way, (rugs, etc), ever; it is new construction after all.

 

[Boil&Toil]

Keep the large picture windows as small as you can, or think about movable insulation, such as shutters. Those things are a big cold hole when it's cold.

Since you had the sense to ask before it was built, do consider gypsum concrete (what's been called "jibcrete" above) on top of the subfloor rather than staple-up. You can tile right over it. You can run wooden sleepers with the crete and tubing in between them, and nail your hardwood to the sleepers. Depending on what you want/do with the floor, you can also skip sleepers and float a floating hardwood floor with no nails, or a thinner "engineered" hardwood that will resist heat passage less then full thickness hardwood. In any case one layer of finish floor will resist heat passage a lot less than a subfloor and the hardwood on top.

Radiators are an option. Radiant wall and ceiling is an option, and either/both should be thought hard about for the taller rooms, especially taller rooms with lots of windows.

Being able to use low temperature water effectively is the "secret" to effective storage that is often missed on the first go-round. If your system tops out at 180F, and you need 150F to make the house warm, you have 30 degrees times the pounds of water stored of heat storage. If 120F water will heat the house, you have twice as much storage without adding any capacity/volume. So designing your emitters (the radiant parts, the radiator parts, etc) to work effectively with "low" water temperatures pays off big time in how long a fully-warmed tank will heat your house. Most oil boiler systems assume 170-180F water at the head of the loop, and you do NOT want storage system designed that way, as you'll have practically none.

Adding more insulation at the design phase will save you money on the size (and effectiveness) of the heating system, and work/money on the amount of fuel you need to make/buy for the entire life of the building. So rethink "not superinsulating" especially if you see -40 on a yearly basis.

 

[JP11]

There's a lot of ways to do what you want. I have a 20x30 living room. Ceiling is 19 foot cathedral. I have A LOT of glass. 6 windows that make up a roman arch. around 14x14 feet of glass.. on each end wall. I have staple up radiant, no transfer plates. 2" foam under the pipes with a 1" air space. Pipe spacing is every 8 inches ( 3 runs per bay, 24" on center floor joists) Runs at 140 to 145 degree temps. works great.
JP

 

[flyingcow]

I'd bet a 1000 would do the job well for you. You should do heat loss calcs to verify that you will have the stored btus you desire between burns. I'd recommend foam or sip's, money spent on insulation is definitely well spent, it can't really be overdone. Personally, I'm impressed with the Garn's simplicity and feel that it's a durable design.
I'LL bet heaterman will chime in with useful advice once he sees Garn in the title.

I agree

 

[Golovkin]

OK - here is what I know now: (thanks to you guys!)

I really need to figure out how to make low-temp water heat as efficiently as possible to maximize the storage capabilities of a Garn Jr. - There is no sense in purchasing such an expensive item if it won't be optimized.

The issue is how to run radiant on a wood 1280sq/ft floor, and I understand these to be my best options:

1. Warmboard - Great performance, fairly easy install, really expensive ($6sq/ft = $7680 just for the board!)

2. Gyp-crete - Great performance, no-one in my area works with this, and I don't like the idea that it may not be durable and prone to water damage.

3. Concrete thin slab - I can probably get someone to do this, the concrete around here isn't high quality, and I'm not sure how much expense will go into engineering a floor to hold the extra 18lbs/sq/ft?

At this point the Concrete option seems the most economical, but I have to figure out if somebody can batch this to a spec that won't crack like mad and also figure out finishing costs, as I imagine the surface will have to be ground smooth

If I go the concrete route - Can I put a wire panel in and zip tie it to the pex to reduce cracking? For the walls do I just put down the base plate before the pour and then they finish to the top?
I imagine I would also block off any areas for counters or a kitchen island, tubs, toilets etc. I suppose I could also block of an area in each room for future pass through's that may arise.

How do you guys feel about a thin slab concrete (1-1/2") over pex?

Your help has been great and much appreciated

 

[heaterman]

We've worked a couple "wet" jobs with a product referred to around here as "litecrete".

It is cement based not gypsum. Not quite as light as gyp to work with, needs to be troweled. The floors perform the same though.

 

[Bob Rohr]

I would not recommend a 1-1/2" thin slab over a framed floor as a finished surface. It's almost impossible to prevent a thin concrete slab from cracking and crazing. You need a very stiff floor framing under a concrete overpower to keep the floor framing from flexing.

You could put a thin hardwood floating floor over a thin concrete pour, or tile, rubber, cork, any thin flooring product would be an option.

Stay away from gyp products in potentially wet areas, even with a sealer and tile application they will come apart when they get wet.

Only after you do some load calc or simulations will you know what type of output in btu/ sq. ft you need. Once you have that info you can determine some heat emitter options. Panel radiators are a great heat emitter, properly sized they can work with 120F supply, add some radiant floors in bathrooms, maybe kitchen floors.

For small bath floors, electric radiant products are a great option, especially with low electric rates.

 

[heaterman]

With any system utilizing storage, and especially a Garn, water temp needed to adequately heat the building is key. The lower you can work with, the more heating time you'll get with your storage.
When I run into someone inquiring about "what boiler", the first question to answer is what water temp is needed to heat the structure and this depends largely on the type of emitter. Fan coils and baseboard are typically going to work best with 160+, under floor radiant can go down to the 140-150 range and a radiant slab will usually work all the way down to 100-110*.

 

[Golovkin]

So this project is finished. and working great.

The house ended up being a 3 story log home 4,500 sq/ft with an attached 30X40 garage.
The Garn jr. is in the Garage and insulated.

The basement and garage runs are in concrete, the main floor and loft were put on 8" or 6" centers in thermofin on top of the sub-floor sandwich style.

The Garn is plumbed to a heat exchanger, and a tekmar 356 outdoor reset that runs two other two pumps (one for mix injection, the other pumps the zones). I used Caleffi manual operators in conjunction with electric controllers tied to thermostats. (manual dials allow the whole house to warm up evenly).

It all works very well and I'm pleased with how it all turned out. Last winter we had some -30f temps and it kept up well, I'm really surprised at how well the system heats even with really low water temps.

My advice to anyone like me that is considering radiant: Learn it all, talk to experts, and DO NOT CUT corners. I often found myself really struggling with the costs and complexity, so the urge to reduce aluminum fin, extend zones, widen centers, and go with cheaper more simple systems was a very strong urge.

Once the job is completed and the system is working, you will see why you can't cut corners, and if you do - there will be a very expensive failure under your feet!

I really thought I was 'Overbuilding' my system, and maybe I did, but the reward is that my system heats very evenly down to really low temps and my storage lasts long. Had I cut corners, the house would have uneven heat and I would be using way more wood to try and keep the tank piping hot. My goal was to only build a fire once a day or every other day in Montana's harsh winter, and I can do that!

So remember my fellow newbies, if you want storage - focus on getting the lowest possible heating temps, or you will have an expensive system that you have to feed like a $500 wood stove...