Building a new house with a gassifier and storage

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mbott

New Member
Sep 30, 2010
2
Danbury, CT
we're currently in the process of getting ready to knock down our house and rebuild (modular). The plan is to go with a eko40 or similar and storage. Originally I was thinking twin 500G propane tanks, but then it dawned on me the other night that we're going to be doing concrete work, why not make an underground cistern and insulate the hell out of it?

Our plan also includes a wall mount propane backup unit for when the fire is unattended. The boiler will be in the basement/garage. We will have 9' walls which I will insulate with foamboard while we do foundation work, 8' garage doors so I can drive my tractor in with a supersack of wood and place it right next to the boiler. the twin tanks really crowds the area, so i was leaning to doing an cistern on the outside of the foundation directly opposite the boiler.
--what considerations do i need to take?
--what access should I maintain for updates, fixes, maintenance?
--best way to plumb and keep it flexible incase of failure or repairs
--special liner or can we effectively have gunite shot in like a hot tub?
--shape of the cistern can be a concern, is it better to be wide and low, or better to be tall and deep?

Our new house will be ~2800 ft, colonial style. 8' ceilings, except the entry way is open to above. We are doing radiant in both floors, my 24x30x12' garage with vaulted ceiling will also be on the system. It will be r20 on the walls and r40 on the ceiling. Radiant in the slab (which we will re-pour since when we do the house) We haven't gotten the pricing back on the cost differences in the insulation options for the house yet but I suspect we're going to go middle-upper of the road in terms of R-value. Same applies for windows.

my goal is to be able to fire once a day (or every other). can you make your storage too big?
we're not planning on going solar at the moment, but may go down that path in the future for DHW so I think non pressurized system is better suited anyways, correct?

Hopefully I'll have more answers than questions soon... thanks!
 
If you search, you will find numerous threads about cisterns/home made tanks. I think the summary is they have to be lined with something like EPDM....which may not hold up very well if you go to higher temps. A cistern presumably is going to be unpressurized, whereas the LP tanks could be pressurized. There's a considerable difference between the two....unpress needs heat exhangers, whereas the pressurized can be directly connected to the rest of the system. I think generally people are very happy with the LP tanks and a pressurized system. You can get to a higer storage temp as well, though with all radiant maybe you'd be happy without the higher temps....depends on your heat load. Do you have a heat load calculation for the building? Ideally your storage would provide all the heat you need for as long as you want to go without firing the boiler...typically say 24 hours.

When you pour your slabs, make sure you use insulation under the slab. 2" extruded polystyrene everywhere in my opinion. Don't even look at the foil bubble wrap stuff....doesn't work at all under the slab. Only have one chance to get the insulation underneath all the concrete.
 
American Solartechnics, makes custom liners made of some proprietary material (not EPDM). I have one of their stock units which uses the same liner and the material looks tough. I believe they do the tanks that Tarm Biomass sells. Tom in Maine on this site owns the firm and I expect he would be glad to talk to you.

If you want to go with coatings, I would not recommend conventional cementitious type coatings as the temperature cycling could cause long term cracks. In general you really want something with some resilience as concrete does move over time and how it relieves stress is by cracking. There are some high end epoxy type systems that are good for 220 degrees or more. Long ago I bought a system for an industrial tank from Stonehard. The tank will require reinforcement with rebar and it has to be placed in the right place.

Another thing to consider is the soils under the house. A water storage tank is heavy and if you have marginal soils, it amy be a challenge to come up with a proper footing. If you are on gravel, it porbably not a issue, but on wet clay you may want a pro to get involved.

Personally I would poor a conventional foundation and install one of tom's stock tanks as if anything ever goes wrong, I can open it up and rehab it a lot easier than a concrete tank. No matter what, you need some sort of liner and insulation on all sides. Tom is bascially selling you precut insulation with some outer reinforcement so it can be assembled in place and the liner. I guarantee you by the time you have formed, rebarred, poured, installed manholes and piping inserts, insulated and coated a concrete tank you will have spent a lot more.
 
The underground tank makes me think of when I had a leak in my water line between my well and my house. It was about 30 Deg. out. That was not good. Luckily, I had access to a back-hoe. I dug up the line where the leak was and fixed it. Then repaired the yard best I could at the time. But I would hate to think what it would have cost me if I had to hire a contractor to fix it for me.

I would not put my storage underground. Something else to consider might be to design and build a small room off of the back of the garage to house your tanks in. That way you still have the room in your garage. Insulate the tanks with closed cell spray foam and insulate the walls of the room and have a door(s) between it and the garage. Or I suppose you could make your whole garage 4' feet longer and have it all in the garage. I tend to think a pressurized system is the way to go. No heat exchangers involved. Not much can go wrong with a pressurized system. Less chance of deteriorating circumstances. With any air getting forced out of the system they seem to work well. I have had my pressurized system with my oil boiler for the entire time I have owned my house. 17 years. No problems. It has been in the house since it was built in 1978. So 33 years. Boy, time flies when your having fun. Have a good one. And good luck with your house and your heating system.
 
If I had the flexibility you have in building I would still go with a pressurized tank. I think I'd ultimately use a single 1,000 gallon propane tank. You reduce your plumbing costs by having one tank and eliminating the need for HX coils. And arguably the performance of a pressurized system "should" exceed that of a non-pressurized system, even if marginal.

Also consider resale of your house. A standalone tank can easily be removed if required. A built-in cistern could be a liability much like a swimming pool can be on occasion, depending on the buyer.
 
For what it is worth, I put 2 inches of insulation around the outside of my basement at garage and then used the bubble wrap with foil stuff under the rest of the floor. I then ran wire and fastened my pex tubing to the wire, and poured my slab on top of it. I have had great results. I am amazed at how much heat the concrete retains. Once it is warm, it does not take much to maintain a comfortable temperature.
 
Thanks for the responses guys. I hadn't even thought about the potential liability thing down the road. I had envisioned it as a 6x6x6 cube about 3' below grade with a removable top (or just using a septic tank, probably the easiest).

I have a backhoe and equipment, so dig-ups weren't really a concern.
I don't have room due to zoning regs to put anything outside like a shed-roof, plus it won't match the house style.

It sounds like the next best thing is to build storage room out of the foundation. the front porch will hide the top of that. it's just a matter of trying to find a tank that'll fit, a 1000 gal tank is 16' long and I've only got about 12' to work with. Any reason to not go with a regular steel water tank? It seems the liability of building a propane tank is higher, hence the higher price tag.
 
If you had to, why not build a concrete "pit" for a metal presurised storage tank? Metal grating at slab level. You'd save the space, have acess and be pressursed. I think that the liability concers will be going away and your system will become an asset instead with all that's going on in this world!
 
Just to clarify I didn't really mean "liability" in terms of legal woes you may experience in the future. I meant it more in terms of resale. Some home buyers will avoid houses with swimming pools for a variety of reasons. I simply feel that if I were building a house I'd want to be able to ditch the tank entirely with minimum effort if I had to in order to make a sale.
 
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