Garage Heat..... Insurance Kosher

[armadillo]

If you ask 100 northern off gridders how they heat their garage/shop, I imagine 95 of them would say "a woodstove". Around here in rural Western Montana, shops are heated with wood. Yes, they store and work on vehicles powered by gasoline engines in these shops and I have never known one to go "boom".
Since the National Building Code does not allow woodstoves in garages, there must be another solution for people who must have homeowners insurance.

The garage/shop I intend to build will be attached to my home, well insulated and about 1500 square feet. I want to maintain winter temperatures between 45 and 65 degrees F. Based on my experiences with other wood heated structures, that would require about 3 cords of pine a winter...if I could burn it in the shop.

Are there any insurance permitted propane direct vent heaters that are efficient?

What about those outdoor wood furnaces? Do they make any without fans? None of my woodstoves ever had fans so I don't see why an outdoor one would need anything more than 20 watts or so to run a circulating pump like this http://www.mavericksolar.net/sdhw/elsid/elsid.htm  to circulate antifreeze thru PEX lines in the shop slab but it seems they all use 150 watts or more to run fans and have complicated control systems.
This is  real dillema for me. Will I have to quadruple the size of my solar system just so I can be insured?

[halfcrazy]

Well I am in central to northern Maine and have a 28 by 48 shop detached. My shop has a trailer furnace (Hot Air) that burns #2 heating oil. I keep it 50-55F all winter and run about 50-70 gallons of oil a season. I would be lost without the heat as we keep out vehicles in there and it eliminated the need to warm them up everyday. I tried to do a wood stove but that was a no go.

Now onto my house. My insurance co just dropped me because I have a new yorker wood boiler in an outbuilding (Small fire resistant building just for the boiler) to heat the slab of the house. I am now working towards a new carrier but man it is tough. One carrier refused us do to having a few chickens, ducks and goats. It looks like State Farm is our best shot they seem to care less about the animals or the boiler.

I told the Wife I am about ready to tell them all to go pound sand and not worry about it. I started with nothing once I suspect I could again

Ryan

[XeonPony]

All insurance companies are in the busines of denying claims to begin with, biggest bs shell game I ever saw in my life, ask what the premium is for the best coverage, now put that into a savings account, by the time you need it you can pay for brand new every thing in cash!

[thirteen]

I tried to get insurance for my house and out biuldings and land just if nothing else to protect me from someone getting hurt on my property. I can replace my house and buildings. No Go. I do not have grid power for my electricial needs. I do not have a foced air furnace. I am to isolated for emergency help. I do not have any acceptable emergency contact available to me. But I can have full coverage insurance on my vehicles. I asked so if some one gets hurt real bad what am I to do,  just have stake them out for the bears.  There was a long pause so I hung up on them. I will try State Farm

[halfcrazy]

Good Luck 
We have state farm on the line now and OMFG what a bunch of morons. We have 2 sheep and 4 goats and they have there panties wadded up cause we have "Wild Animals" Man a working guy sure can not get ahead today can he?

Ryan

[thirteen]

Tell them they are mine and I rent the pasture from you and use them as payment.

[halfcrazy]

Well god love mt wife she is still on the phone with the State Farm guy (Ironic State Farm is worried we have a Farm? WTF) and they are making progress. Seems as long as we do not make a profit on the animals we are ok. She told them not to worry there was no danger of this place turning a profit as long as I keep blowing things up 

Ryan

[gww]

armadillo
I would like to point out that if you go to an outside wood burning stove, no matter what you do,  your 3 cords are out the window.  All the outside wood burners I have ever seen would use 4 times that much.  I have personal exsperiance with wood hot water "hardy type" and an outside insulated blower one.  I had a "Johnson"  in my basement hooked through my furnace duct work and it used 3 cord.  Missouri
gww

[dnix71]

State Farm is the problem, not insurors in general. Here is south Florida they are dropping all wind storm (hurricane) policies but not dropping auto, fire or liability. They cherry pick because those in the state government who are supposed to regulate this are corrupt and allow it.

That said, there are more honest underwiters out there. I have had Progressive for many years with no trouble.

[Frank S]

Well god love mt wife she is still on the phone with the State Farm guy (Ironic State Farm is worried we have a Farm? WTF) and they are making progress. Seems as long as we do not make a profit on the animals we are ok. She told them not to worry there was no danger of this place turning a profit as long as I keep blowing things up 

Ryan

I I remember correctly half of their company name is FARM DuH? But then again the other half is STATE which implies that they are the controller no matter what.

[ChrisOlson]

I have two shops - my small turbine shop is 18 x 30 and I heat that with solar hot air panels that I built and mounted on the south facing wall.  For backup I have a small 50,000 BTU fuel oil furnace and I burn #2 off-road diesel fuel in it.

My equipment shop is 60 x 120 and I heat that with an outdoor Northland hot water stove with two Modine heat exchangers in the shop.  But I haul wood in by the semi load for it and I own a skidder so I can do the logging to fuel it.

Due to the amount of wood it takes I don't heat the equipment shop in the winter anymore.  And once it gets cold in there it takes a full cord just to heat it up to 60 and get the concrete semi-warm again.  Plus we don't have power in the equipment shop unless I run a generator because the power draw of the shop is way more than you could run with any sort of inverters.

So I "fixed" that for this coming winter.

I recently bought a Lanair 200,000 BTU used oil burning furnace for the equipment shop that burns used engine oil and it operates on 120 volt power.  We generate about 1,400 gallons of used oil per year and the oil is stored in an old below-ground 1,000 gallon fuel tank that we had to dig up due to new state laws on below ground fuel tanks.  I have the tank in the unheated portion of my machine shed in a concrete dike.  The used oil furnace is going to keep the equipment shop at 45-50 degrees so the concrete doesn't get cold in there this year.  Then, if I want to work in it I'll fire up the hot water furnace and heat it up in there.  The Lanair will run off 120 volt power from our house system.

Our insurance had some issues with the used oil heater having to have its oil supply within 20 feet of the furnace.  And the oil has to be kept reasonably warm so it will flow.  However, over half of the waste oil we generate is hydraulic oil so it flows really good even in sub-zero temps.  It turned out that with a little booster pump in the line it could draw oil off the storage tank in the machine shed with no problems.  An insurance inspector came to our place and looked it over and said it was OK.

So that's something new we're going to try this year.  Waste oil has incredible amounts of heat in it compared to #1 fuel oil and that 200,000 BTU furnace only uses 1.4 gph running constantly and draws 1.6 amps to run the burner gun and fan in it.  I expect it will be about 50% duty cycle in really cold weather so it should take about 17 gallons of oil per day to fuel it.

Our insurance carrier is Rural Mutual.
--
Chris

[armadillo]

Thanks for the replies, guys.

I tried to get insurance for my house and out biuldings and land just if nothing else to protect me from someone getting hurt on my property.

My property is 185 acres former timber company land and historically used by hunters and ATV'ers. It's really all about "insurance against lawyers".
I can survive fire, windstorm, hail, lightning other acts of god, but I can't survive acts of courts.
I've spent 25 hours in the last week studying outdoor boilers and in slab radiant heat used in conjunction with a propane water heater and 24 volt circulation pumps. My conclusion is that in addition to about $1400 a year for insurance, my cost to be covered will be another $1000 a year.

Maybe I will get a policy when the shop is in dry in stage without woodstove installed, then do as I please and hope they never find out. I don't think they can deny a liability claim from a tresspasser because they find out later that I have a woodstove.

[DamonHD]

I think that many insurers may take the view that if you deliberately lie to them about *any* part of your application for coverage then they may void *all* of it.

Rgds

Damon

[Bruce S]

armadillo;
You might contact Gary over at www.builditsolar.com.
He up around Bozeman,MT and I'm pretty sure he could help you with maybe outfitting the garage with solar heat instead of wood or fuels.
Go check out his website too it is full of stuff he's done.
Can't help with the insurance other than maybe look for underwriters instead.
I've not gone with a "brand-name" insurance since State Farm dropped me 'cause a kid broke his tooth in my backyard  . Never mind the fact that I'd been instance free for 10 years!
Gary posts here as well.
He goes by the user name here as garygary.
Hope that helps
Bruce S
 

[armadillo]

armadillo;
You might contact Gary over at www.builditsolar.com.
He up around Bozeman,MT and I'm pretty sure he could help you with maybe outfitting the garage with solar heat instead of wood or fuels.

Interesting website, thanks. I'll spend some time checking that out.
I'm pretty ignorant about passive solar systems. In the winter we only have about 2 sunny days a month. PV works OK on the few minutes of sun we get here and there between clouds and seems to keep up on completely overcast days if the load is light. I run the generator/battery charger about 20 days a year to top off the batteries, mostly due to snow on the roof PV panels. Most of the winter it's 20 degrees by night and 30 degrees by day with a couple spells of minus 10 or 20. Do you think passive solar is feasable under those circumstances?

[Bruce S]

I'm down in Missouri, so my opinions would be based on my area.
BUT Gary seems to be doing okay up in Montana too.
He would be a better judge for your area.
He's built quite a bit, even a heating system based on stored water heated from solar.
The biggest difference between PVs and Solar heat are 1) Much much cheaper to build 2) Can take advantage of any SUN shine, the fans to push or pull the heat through would only need not much more than an old Muffin fan or two.
Shoot him an email, and see what he has to say.
As a side note, those Beer can heat grabbers are awesome and quick to build!! You'd be amazed and the heat available during a few short sun hours.
I'll also shoot him a PM to see if he'd chime in here.
Bruce S

[GaryGary]

armadillo;
You might contact Gary over at www.builditsolar.com.
He up around Bozeman,MT and I'm pretty sure he could help you with maybe outfitting the garage with solar heat instead of wood or fuels.

Interesting website, thanks. I'll spend some time checking that out.
I'm pretty ignorant about passive solar systems. In the winter we only have about 2 sunny days a month. PV works OK on the few minutes of sun we get here and there between clouds and seems to keep up on completely overcast days if the load is light. I run the generator/battery charger about 20 days a year to top off the batteries, mostly due to snow on the roof PV panels. Most of the winter it's 20 degrees by night and 30 degrees by day with a couple spells of minus 10 or 20. Do you think passive solar is feasable under those circumstances?

Hi -- this is Gary from Bozeman.

This is the solar shop heater that Bruce mentioned: http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
There are a lot more designs here: http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm
You are welcome to come a have a look next time you get to Bozeman.

As it turns out, Paul House from Bozeman Biofuels is installing an 80 ft wide by 10 ft high modeled after my shop collector on the Eagle Mount barn/exhibit place this weekend.   http://eaglemount.org/
This will be the biggest one I know of -- about 130K BTU/hr output.

Anyway, the collector does a great job on sunny or part sunny days as long as the building is insulated and you make the collector large enough -- mine is 160 sf of collector to heat about 600+ sf of shop insulated to R19.   70F inside on a 10F day is pretty normal.

This is another way to go that I like even better: http://www.builditsolar.com/Projects/SpaceHeating/SolarGarageCollector/garcol.htm
The combination of solar lighting and solar heating is hard to beat

As it happens, I was thinking of adding a small wood burner to the shop for those cloudy days.  Our State Farm Agent (who has done a good job for use over time) said that they will absolutely NOT insure any kind of shop heated with wood -- no exceptions.  He is OK with a wood burner in the house as long as its put in correctly, but not in a shop.  Oh Well.

Gary

[armadillo]

Thanks Gary. There is less sunshine in Superior, Mt. than Bozeman, Mt. in the winter.
http://www.city-data.com/city/Superior-Montana.html
http://www.city-data.com/city/Bozeman-Montana.html

The shop will have an East-West roof ridge to accomodate PV panels for the home and shop so I won't have the large South facing Gable end wall to soak up the rays, but it might be feasable to have 6 or 7 foot tall collectors on the South facing wall under the eaves. That might mean shoveling snow on that side though.
Since I can't have a woodstove as a backup for coldest days, I could install a radiant in slab heater to run off a propane water heater, which would cost about $3500 with me doing the work.

[armadillo]

As it turns out, Paul House from Bozeman Biofuels is installing an 80 ft wide by 10 ft high modeled after my shop collector on the Eagle Mount barn/exhibit place this weekend.   http://eaglemount.org/
This will be the biggest one I know of -- about 130K BTU/hr output.

Those numbers just struck me....about 1.6K BTU per square foot...that's pretty damn impressive!

[GaryGary]

As it turns out, Paul House from Bozeman Biofuels is installing an 80 ft wide by 10 ft high modeled after my shop collector on the Eagle Mount barn/exhibit place this weekend.   http://eaglemount.org/
This will be the biggest one I know of -- about 130K BTU/hr output.

Those numbers just struck me....about 1.6K BTU per square foot...that's pretty damn impressive!

I wish

The incoming sun is about 300 BTU/sqft  per hour in good sun, and with a bit over 50% efficiency you get about 160 BTU/sqft sqft of collector  per hour delivered to the shop.  For the 800 sqft collector that's about 130K BTU per hour to the shop.  That's output, so an equivalent furnace with 80% efficiency would have to be about a 160K BTU/hr input furnace.  Of course the furnace can run anytime and the collector only runs when the sun is on it -- but it does not use much gas

Gary

[armadillo]

Since I will need to back up solar with something else for overcast, snowy and extreme cold weather, I guess solar hydronic would make sense because it could be designed as a propane/solar hybrid. I've been hunting the net trying to find design drawings for such a system but all I found was complicated systems which include domestic hot water heating, which I don't want since the distance is too great.
I assume such a system could stand alone and use anti-freeze, thus not needing heat exchangers or storage tanks other than the propane water heater. I want simplicity so I could diagnose malfunctions myself.

[GaryGary]

Since I will need to back up solar with something else for overcast, snowy and extreme cold weather, I guess solar hydronic would make sense because it could be designed as a propane/solar hybrid. I've been hunting the net trying to find design drawings for such a system but all I found was complicated systems which include domestic hot water heating, which I don't want since the distance is too great.
I assume such a system could stand alone and use anti-freeze, thus not needing heat exchangers or storage tanks other than the propane water heater. I want simplicity so I could diagnose malfunctions myself.

One thing is that the solar air heating collector linked to above is very very simple -- no fans, no controllers, no moving parts other than the 2 cent plastic film damper.   Materials costs about 8 years ago were just a bit of $2 per sqft -- kind of amazing -- about a 1 season payback.   It has gone through the 8 years with zero maintenance.  But, its still a very efficient collector.   To keep this simplicity, I'd think about a backup heater that does not tie into the solar -- perhaps a regular propane air heater.

But, you can do the solar hydronic plus propane system. 
In most of these systems, there is some storage -- I'm not sure if you could do it with no storage.
One common scheme is a common storage tank that is heated by solar and also heated by a backup heater like a propane boiler (probably a proane tankless water heater could be used). 

Here are some examples:
Tom's system: http://www.builditsolar.com/Projects/SpaceHeating/TomLargeCol/TomCol.htm
This uses a large common tank with solar collectors, wood heat backup, and hydronic heat distribution.

Norm's system: http://www.builditsolar.com/Projects/SpaceHeating/DHWSpaceBoiler/DHWSpaceBoiler.htm
This uses the same sort of common tank and solar and propane boiler backup.

http://greengateguesthouse.blogspot.com/search/label/Solar%20Projects
This one has no storage tank, but uses the floor slab as storage.

More here: http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

All of these work well, but the bottom line is that they will be more expensive, more work to install, and more maintenance compared to the air system -- but, they also give you more flexibility.

Gary

[armadillo]

But, you can do the solar hydronic plus propane system. 
In most of these systems, there is some storage -- I'm not sure if you could do it with no storage.
One common scheme is a common storage tank that is heated by solar and also heated by a backup heater like a propane boiler (probably a proane tankless water heater could be used). 

Thanks, Gary. If a solar/propane hydronic heating system has a 50 gallon propane water heater, why can't the water heater be the storage for whenever the solar system is in operation?

[GaryGary]

But, you can do the solar hydronic plus propane system. 
In most of these systems, there is some storage -- I'm not sure if you could do it with no storage.
One common scheme is a common storage tank that is heated by solar and also heated by a backup heater like a propane boiler (probably a proane tankless water heater could be used). 

Thanks, Gary. If a solar/propane hydronic heating system has a 50 gallon propane water heater, why can't the water heater be the storage for whenever the solar system is in operation?

I guess this means the hot water tank has one circuit that pumps water out to hydronic radiators, and a 2nd circuit that receives heat from the solar collectors?


I don't claim any great expertise in this, but here are some thoughts on a 50 gallon hot water heater based system:

- 50 gallons is not much storage.  If you heat it to (say)140F, and use the heat in it until its down to 80F, the heat energy is (50 gal)(8.3 lb/gal)(140F - 80F)(1 BTU/lb-F) = 25K BTU  -- about equal to 1/4 gallon of propane.  Maybe not enough to do a lot of good in heating the building up?

- 50 gallons is not enough storage to support a whole lot of collector area -- the usual rule of thumb is about 1.5 gallons per sqft of collector, so about 33 sqft of collector.  This is not likely to be enough solar collector to put a big dent in the shop heating unless the shop very very well insulated.   I think that 3 to 5  times that area would be more typical for a garage size shop in a cold climate with typical insulation.

- The collectors have to be protected from freezing, so the circuit out to the collectors has to be antifreeze and unless you want to make the whole 50 gallons in the hot water tank antifreeze, then there has to be a heat exchanger between the collector circuit and the hot water tank.  This could be a coil embedded in the tank (kind of pricey), or heat exchanger outside the tank that tank and collector water is circulated to -- this means two pumps.

-  You would have to work out how the heating element in the tank is controlled.  If you let it just maintain 140F (or so), then there is no water available for the solar collectors to heat up -- its already hot.
You would have to do something where the solar heated the water in the tank from a low temperature, then the solar heat in the tank is used, then the burner on the tank comes on and heats the water after the solar is used.  I've not heard of anyone doing this, but maybe its possible.

You might take a look at Guy's system: http://www.arttec.net/Solar/BarnHeat.html
I don't remember all the details, but its a shop with hydronic heat and propane backup.  I think he uses a tankless heater for the backup, but don't remember for sure.
His hydronic heat is in floor radiant, but hydronic baseboards should work the same way, other than not providing any extra storage thermal mass.

I may be missing something here -- anyone else have ideas that might be simpler?

Gary

[armadillo]

Thanks for your help, Gary.

I guess this means the hot water tank has one circuit that pumps water out to hydronic radiators, and a 2nd circuit that receives heat from the solar collectors?

I think that would be neccessary.

- 50 gallons is not much storage.  If you heat it to (say)140F, and use the heat in it until its down to 80F, the heat energy is (50 gal)(8.3 lb/gal)(140F - 80F)(1 BTU/lb-F) = 25K BTU  -- about equal to 1/4 gallon of propane.  Maybe not enough to do a lot of good in heating the building up?

I guess I don't understand the idea of water storage in the solar circuit. The slab would store heat, the propane water heater would recover every hour or so when in use.

- The collectors have to be protected from freezing, so the circuit out to the collectors has to be antifreeze and unless you want to make the whole 50 gallons in the hot water tank antifreeze, then there has to be a heat exchanger between the collector circuit and the hot water tank.  This could be a coil embedded in the tank (kind of pricey), or heat exchanger outside the tank that tank and collector water is circulated to -- this means two pumps.

I was thinking that all of it would be filled with antifreeze, so what is the purpose of a heat exchanger? Domestic hot water will not be in the system.

-  You would have to work out how the heating element in the tank is controlled.  If you let it just maintain 140F (or so), then there is no water available for the solar collectors to heat up -- its already hot.

I was thinking that the propane water heater would be in the "pilot" mode whenever there is sun in the forecast. If it's snowing or nightime, I could just turn the knob from "pilot" to "on" if I wanted to work in the shop.

I don't understand why some people use tankless heaters in these applications. They require operating pressure of 40 PSI and since there is a pressure drop of 4 PSI or so across them, more pump watts would be needed to overcome that. Besides, if water storage is desired, why use a tankless? Just for faster recovery?

I've seen a lot of drawings showing DHW system being used to keep back pressure on the space heating circuit. Why would I need more than 10 PSI? I was thinking a tank and automotive radiator cap on top of the water heater instead of the expansion tank and air eliminator. That way gravity would remove bubbles and a sightglass on the tank would indicate level and I would have eliminated three items that complicate diagnosis of problems.

Thanks for your time, I'm trying to wrap my head around this.

I haven't given up on your suggestion of installing solar air heat, but I would probably still use propane hydronic as a backup. You had suggested a propane air heater but I don't think there are any made that make sense for off grid. The beauty of hydronic is that the only power needed is a few watts DC.

[GaryGary]

Hi,
I missed that your slab had the pipes embedded in it for hydronic heating.  That would indeed add some good thermal storage for the solar system.  Hopefully there is insulation under the slab?

It seems like system at Green Gate Guest house is pretty close to what you want to do: http://greengateguesthouse.blogspot.com/search/label/Solar%20Projects

And, Guys system is also pretty close.

If you use the tank instead of the tankless heater, then you could fill the whole system with antifreeze, but most people don't like buying that much antifreeze or dealing with it.  The up side of filling the whole system with antifreeze is that if the shop should ever go cold for a long period, you would not have to worry about anything freezing.  The downside is that in addition to the initial cost of the antifreeze, you have to check it every year and possbily change it every 3(?) years or so.

I think the appeal of the tankless is that its compact and it does not require storing a lot of water/antifreeze.  You may be able to cut the flow rate back a bit and get that 4 psi down while still carrying enough heat.  The one I had was basically just a coil of a few feet of half inch copper -- I did not measure the pressure drop, but I'd guess it was small. 
It would be good to read up on Guy's system as it covers pretty well all the components that are needed for a closed antifreeze system and the procedures for filling it etc.


Closed systems typically have an expansion tank to pressurize the system, and part of the initial charging of the system is blowing up the expansion tank to the required pressure. 

All this talk about complications of closed loop systems reminds me why I really like drain backs

One characteristic of the slab system like this is that it reacts slowly.  So, you can't come into the shop at 7am, give it a blast of heat from the backup system, and then let the solar air heating collectors take over as the shop warms -- the slab just responds to slowly for that approach to work.

Gary

[armadillo]

Thanks, Gary. The slab is not poured yet. If I go hydronic, I'll use 2" of foam insulation underneath.
I do want the system designed with glycol throughout to facilitate winterizing in case I have to go to a hospital or prison in the middle of winter.

Tankless heaters do have flow sensing hardware that restricts flow. I have a tankless water heater in my home and deeply regret my decision to buy one, as I would have to do major tear out remodeling to convert to tank type. I always advise people not to go tankless if they have less than 40 PSI water pressure or hard water. Do not believe what the manufacturers say about these pressures.

I've been studying the links you provided the last few days. One design limitation is that my south wall is under eaves and due to overhangs any wall mounted collector (which is what I would prefer) could only be about 5 1/2 feet tall.
If I went with solar air heat, I'd build the collectors myself, but if I go hydronic I would buy new or used collectors and I'm concerned about cost and availability in such a short height.

I guess I could go with long roof mount solar water collectors, but there is no way I could bring myself to cut big holes in a perfectly good screwmetal roof. Do people ever route the collector water lines up under the ridge cap to avoid this?

[Frank S]

Hi,
I missed that your slab had the pipes embedded in it for hydronic heating.  That would indeed add some good thermal storage for the solar system.  Hopefully there is insulation under the slab?

It seems like system at Green Gate Guest house is pretty close to what you want to do: http://greengateguesthouse.blogspot.com/search/label/Solar%20Projects

And, Guys system is also pretty close.

If you use the tank instead of the tankless heater, then you could fill the whole system with antifreeze, but most people don't like buying that much antifreeze or dealing with it.  The up side of filling the whole system with antifreeze is that if the shop should ever go cold for a long period, you would not have to worry about anything freezing.  The downside is that in addition to the initial cost of the antifreeze, you have to check it every year and possbily change it every 3(?) years or so.

I think the appeal of the tankless is that its compact and it does not require storing a lot of water/antifreeze.  You may be able to cut the flow rate back a bit and get that 4 psi down while still carrying enough heat.  The one I had was basically just a coil of a few feet of half inch copper -- I did not measure the pressure drop, but I'd guess it was small. 
It would be good to read up on Guy's system as it covers pretty well all the components that are needed for a closed antifreeze system and the procedures for filling it etc.


Closed systems typically have an expansion tank to pressurize the system, and part of the initial charging of the system is blowing up the expansion tank to the required pressure. 

All this talk about complications of closed loop systems reminds me why I really like drain backs

One characteristic of the slab system like this is that it reacts slowly.  So, you can't come into the shop at 7am, give it a blast of heat from the backup system, and then let the solar air heating collectors take over as the shop warms -- the slab just responds to slowly for that approach to work.

Gary

I have or possibly by now had a friend up in the PNW his house sat over his garage the garage was 2500 sq ft with embedded pipes they were on 12 " centers throughout the entire slab the roof was a standing seam copper the design of hte house with a 12/12 pitch and long eave overhangs 3 story with a huge covered balcony gave it nearly 6000 sq ft of area entirely covered with hydronic solar through automatic valving  which ever side was receiving the highest thermal circulated through the slab.
 low sun days and nights heat for the system was provided by an automatic sawdust / wood chip fed Propane ignited  boiler. Heat for the entire house was provided by what is known as a Siberian stove & chimney basically  a huge mass of stone & concrete with heat exchange tube routed through it Richard told me it had a little over 35 tons of stone & concrete the fire on the ground floor or garage was also dust/chip fed 3 fireplaces on the next floor built into the system could be used and 1 large fire place on the top floor in the den even the outdoor 6 person hot tub on the top floor balcony was heated by the dust/chip fire

[GaryGary]

Thanks, Gary. The slab is not poured yet. If I go hydronic, I'll use 2" of foam insulation underneath.
I do want the system designed with glycol throughout to facilitate winterizing in case I have to go to a hospital or prison in the middle of winter.

Tankless heaters do have flow sensing hardware that restricts flow. I have a tankless water heater in my home and deeply regret my decision to buy one, as I would have to do major tear out remodeling to convert to tank type. I always advise people not to go tankless if they have less than 40 PSI water pressure or hard water. Do not believe what the manufacturers say about these pressures.

I've been studying the links you provided the last few days. One design limitation is that my south wall is under eaves and due to overhangs any wall mounted collector (which is what I would prefer) could only be about 5 1/2 feet tall.
If I went with solar air heat, I'd build the collectors myself, but if I go hydronic I would buy new or used collectors and I'm concerned about cost and availability in such a short height.

I guess I could go with long roof mount solar water collectors, but there is no way I could bring myself to cut big holes in a perfectly good screwmetal roof. Do people ever route the collector water lines up under the ridge cap to avoid this?

Hi,
Usually, overhangs are not too much of a factor for mid winter space heating because the sun is so low -- spring and fall can be more of a problem, but even fall is usually not too much of a problem because the sun is getting pretty low by the time cold weather comes.  Late spring can be a problem with overhangs here in MT as the cold weather hangs on and the sun is getting higher in the sky.

There is a good overhang tool here: http://www.susdesign.com/tools.php
Or, better yet, you can do a simple model in Sketchup, which has a built in sun -- an example: http://www.builditsolar.com/References/SketchUp/SketchUpEx.htm

The cost per sqft between commercially made water heating collectors at about $30+ a sqft and homemade solar air heating collectors at about $2.50 ish a sqft sort takes your breath away  

Not trying to sway you away from commercial water heating panels (well, maybe I am , but the limited height fits well with the homemade "hizer" design idea.
http://www.builditsolar.com/Projects/SpaceHeating/RobHizer/RobHizer.htm
http://www.builditsolar.com/Projects/SpaceHeating/Hiser/Hiser.htm

Gary

[armadillo]

The cost per sqft between commercially made water heating collectors at about $30+ a sqft and homemade solar air heating collectors at about $2.50 ish a sqft sort takes your breath away  

Thanks, Gary. Does a square foot of air heat collector produce about the same heat as a square foot of water heat collector? Most people spend more than $2.50 a square foot just on siding, LOL.

[GaryGary]

The cost per sqft between commercially made water heating collectors at about $30+ a sqft and homemade solar air heating collectors at about $2.50 ish a sqft sort takes your breath away  

Thanks, Gary. Does a square foot of air heat collector produce about the same heat as a square foot of water heat collector? Most people spend more than $2.50 a square foot just on siding, LOL.

If you look at the ratings in the SRCC ratings section, the water heating collectors tend to do a bit better in efficiency. 
https://secure.solar-rating.org/Certification/Ratings/RatingsSummaryPage.aspx
But, the difference is not large.

I've had a go several times at measuring the efficiency of the thermosyphon air heating collector on my shop, and it has come out very good. 

If the air collector is going up as a part of the initial construction, it would be possible to not do siding under it and put a layer of polyiso insulation in as the back of the collector -- this insulation could be your wall insulation for that area.  So, you save some money by having the collector glazing be the siding and the collector insulation be the wall insulation.  I guess one could even go a step further and build the collector right into the south wall -- I think it could be made compatible with 24 inch stud spacing with extra deep studs?

Gary

[armadillo]

Good idea about built in collectors, Gary.
The building will be a pole barn with treated 6x6 posts every 8 feet. Lots of room for a collector inside.

[MattM]

If you are building it yet then consider how to not use it in the part of the year its already hot.