off grid, barrel stove, old cast iron radiators, 1” Pex HELP

skimiemo

12x40 lofted barn cabin, off grid, barrel stove, 4 large old cast iron radiators, 1” Pex, nothing in place or assembled, HELP. thought this would be a simple, cost effective way(without tons of wood burn) to heat the cabin. plan: radiant 1” pex floor. not sure of radiator fitting/pipe size(bigger) to 1” pex... will this circulate naturally? pumps not an option. possible?

Jamie Hall

A lot of buildings were heated by gravity hot water at one time. It's fundamentally simple and reliable. It is not, however, necessarily that simple to get it set up right, and it is very much dependent on low flow resistance in the system -- and balanced flow resistance.

Nice generalities. Now. Things to think about. First, your heat emitters -- the radiators -- must be above the heat source, and the greater the height difference the better, since your circulation is being driven by hot water at low density coming off the top of the heat source, rising the radiation, and cooling there and coming back down the return lines to the heat source again. There isn't all that much force available to drive that -- the difference in density is all you have to play with -- so gravity systems tend to have very large pipes; comparable to or even bigger than steam. 2 inch, 3 inch, not uncommon.

I suspect you could use a radiant floor as part of the return system -- although you would have no independent control of it -- provided that you arranged it for parallel flow with manifolds at the ends designed to direct the same flow to each pipe (I can think of several ways to do this; a system with large diameter manifolds set up as reverse return might be the simplest). A conventional looped piping system is going to have too much flow resistance for a gravity system. That floor could be on the same level as the heat source, but only provided that the radiators are significantly higher (like the next floor up) to give you a driving force.

Intriguing...

Larry Weingarten

Hi, I built an off grid home with radiant in the walls. As Jamie kinda says, height is your friend. Also, you want to make sure air always has an easy way out. One little bubble can kill circulation. I'd downfeed to the radiators if possible as they help drive the system by cooling the water. Let the hot water fall into and through them, back to the bottom of your hot water storage.

A really good shell is important for your cabin so you're not making the system work too hard. My main line is 1-1/4" for an 1800 square foot house, but I built with SIPS and took pains to make it tight. Also, my temps are not too extreme, measured from 18 to 105 degrees.

One other fun thing is that each radiator will act as its own variable speed pump. When colder, water flow will speed up, keeping the system in balance.

Yours, Larry

leonz

skimiemo said:

12x40 lofted barn cabin, off grid, barrel stove, 4 large old cast iron radiators, 1” Pex, nothing in place or assembled, HELP. thought this would be a simple, cost effective way(without tons of wood burn) to heat the cabin. plan: radiant 1” pex floor. not sure of radiator fitting/pipe size(bigger) to 1” pex... will this circulate naturally? pumps not an option. possible?

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You have a pig in a poke now;

The only way your going to obtain adequate heat this coming heating season is to put a coal/wood stove in the cabin on one wall and run the flue pipe through the wall if you have a clay thimble through the wall you will have no issues with the US Stove Wonderlux as it does not require power to run it and it has a built in cook top from what I remember.

Your going to end up with a US stove Wonderlux model wood and coal stove from Tractor Supply to heat the place since your off the grid.

Short of planning on a gravity fed hot water boiler with a manual damper below ground and attached to the foundation wall to connect your pex to a open to air expansion tank with the vent through the roof. Just be sure to use steel piping close to the boiler before you begin using the 1 inch pex and the four cast iron radiators later you have few if any options as the wonderluxe wood coal stove will carry a fire for a very long time as long as you properly manage it if you use nut anthracite coal.


DO NOT run steel pipe and elbows in your barrel stove to heat the water its a guaranteed visit to the cemetary.

nibs

Have been using a barrel stove for about 4 years to heat our hot tub, which we use at least 5 or 6 days a week. (did not use it last night because of a thunder storm). The folks on this site are experts on the heat system, but maybe I can help with the barrel stove.
We took a second barrel, took off the ends and slit it, put it inside the first barrel with rock wool between the two.
We used galvanized 1 1/2" pipe in the boiler an arrangement of pipes and elbows over the fire, and to collect the return and hot pipes. Our tub ( a 300 gallon hill billy stock tank) is 5 ft away from the barrel and about 16" above it. We also extended the chimney down into the firebox about 1/2 way, not sure if that made a difference.
You will find that when the water in the firebox pipes is cold, the fire will be smokey, burning small pcs of good dry wood is needed to get the fire hot enough to burn well.
A couple of thoughts, on a cold day or night you will be feeding the fire constantly, unless you have a storage tank, when the fire is out, the system will still thermo syphon and the boiler will be cooling the water/house.
You might put part of the in boiler plumbing up the inside of the chimney to feed the second floor first. The barrel stove will boil the water in the pipes so you need to have an open system with the supply water going into an open tank on the second floor.
Barrel stoves put out a massive amount of heat, so were I you
I would put the barrel stove inside the house and use it as a space heater. Or find an outdoor boiler and find a way to run a circulation pump, (solar or wind possibly).
Listen to the experts (not I sir) there is a massive body of knowledge here.

Solid_Fuel_Man

So, I'm confused. You would like to install a wood boiler to heat your off-grid place with gravity circulated water? Or something to do with a barrel stove?

First off, the barrel stove is not only very inefficient it is also quite dangerous. I would not want a fire separated from my living space with some 16ga sheet metal.

There is some science to burning wood efficiently, and also to making water circulate through pipes all on it's own. With some planning both can be had, but it will cost both time and some money to build something which is both safe and efficient. Pipe diameter, and elevation are two keys for a good gravity water system.