Home Brew Tent Heater (1 Viewer)

[EricG]

Started a new project today - hoping to make the tent a little more comfortable late & early season, and at altitude. I've read the Mr. Heater thread, and I know people have been happy with them. But between the fire and CO risk, I just can't see myself sleeping well one of those. I like the Zodi heaters, but they apparently aren't available any more, so I'm working on my own solution.

My starting point is a 10K BTU Coleman 1 burner stove:
http://www.amazon.com/gp/product/B0009PUR5E/ref=oh_details_o01_s00_i01?ie=UTF8&psc=1

And a 4" 12V bilge blower:
http://www.amazon.com/gp/product/B000O8D0IC/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

I've procured a piece of 6" square aluminum tube to house the heat exchanger - 5 pieces of 1" diameter aluminum tube through the section. Two pieces of 4" tube on the outside attaching the ducting.

I've assembled the structure so far with the Alumiweld brazing rods from Harbor Freight:
http://www.harborfreight.com/8-piece-low-temperature-aluminum-welding-rods-44810.html

I'm pretty happy with the result so far - could use some more practice with the brazing. I've run a bead of caulk around the end of the channel and sealed it to a plate - once it cures I'll fill it with water and see how good my joints are.

Still to do - some internal baffles and a lid to keep the heat in there. 6" is a little to large, but it fits well on the burner. And some way to support to unit on top of the burner, ducting, power, etc. More to come.

 

[EricG]

One more pic, glued down for the leak test, and with the burner & blower in the pic.

 

[EricG]

Well, the first leak test failed pretty badly. Looking closer, it appears that the brazing cracked/separated from the main tube. I suspect this is from thermal stresses - thought I heard a pop from the far side when I was working on the near side. Not sure what to do about that - try to get a more even heating and slower cool down I guess.

 

[landcrshr]

Looks like something similar to an idea I had to repurpose an old tabletop gas grill.
If only I had the fabrication skills to build the heat exchanger into the grill's lid.
I will be interested to see how it turns out.
Thanks for the idea on the bildge blower.

 

[EricG]

Looks like this isn't going to work until I come up with a better way to assemble the heat exchanger. My welding skills are definitly not up to the task!

Tried again last night - preheated the whole thing in the oven, then brazed it again the put it back in the oven to cool down slowly. Heard it popping as I was carrying it back to the oven. It looks better, but it still leaks pretty badly.

 

[myquestoyota]

For what your time is worth take it to the local sheet metal/heating place and have them do the assembly for you. then sell us one.

 

[EricG]

For what your time is worth take it to the local sheet metal/heating place and have them do the assembly for you. then sell us one.

Not really worried about my time - hobbies & side projects don't have to conform to Occams Razor. But not interested in beating a dead horse either, and I'm not sure I see promise in the brazing approach, at least with aluminum. I'm just not convinced it's really bonding well. Some places it doesn't really appear to be "wetting" the base metal despite extensive cleaning, different levels of heat, etc. Maybe with steel though - I have a small brake and could probably at least form an open ended tube.

I've thought about shopping it out also, but it seems like heat & AC shops typically just assemble already manufactured components. They don't build their own heat exchangers. Sheet metal place might be able to do it. Machine shop could hog the whole thing out of a billet

I've done alot of googling for ready-made heat exchangers but haven't found anything at this scale of the air-to-air variety.

 

[Bogo]

Use flange fittings to make the seams have larger contact areas or learn to weld better. Yeah, your brazing job doesn't have to support weight, but it does have to deal with heat stress and the expansion and contraction of parts at different temperatures.

 

[EricG]

Use flange fittings to make the seams have larger contact areas or learn to weld better. Yeah, your brazing job doesn't have to support weight, but it does have to deal with heat stress and the expansion and contraction of parts at different temperatures.

I've looked for flange fittings - didn't find anything like this. Any suggestions?

I've thought about using a flaring tool on the tubes, and a dimple die to punch the holes. If they matched up well, you could have a better surface area.

The brazing of the big 4" rings is actually pretty strong - I've smacked them pretty hard with a mallet. But those smaller tubes so close together just isn't working.

 

[nat]

Why not buy one of the inexpensive readily available heat exchangers?

 

[EricG]

Why not buy one of the inexpensive readily available heat exchangers?

Link? I haven't been able to find one.

 

[rusty_tlc]

I'd be concerned about the brazing fracturing over time with heat expansion/contraction. The last thing you want is to start blowing CO into the tent while you are asleep.

You probably need to use slightly thicker material and TIG it together.

 

[e9999]

Nice creative job. But i don't think your tubes are going to be very effective heat exchangers. Usually air heat exchangers have to have a lot of fins to be able to transfer heat effectively.
As far as the brazing issue, you could also just extend the small tubes out and connect your air duct directly to them. Any small leak -although a heat loss- would not be an issue for CO, and you could goop it up too.

 

[greentruck]

Started a new project today - hoping to make the tent a little more comfortable late & early season, and at altitude. I've read the Mr. Heater thread, and I know people have been happy with them. But between the fire and CO risk, I just can't see myself sleeping well one of those. I like the Zodi heaters, but they apparently aren't available any more, so I'm working on my own solution.
SNIP

It's worth noting that the Mr. Heater models have been tested and approved so that when used per instructions they're safe. I applaud your craftiness, but the issues with the welds point out this is an area where the DIYer is going to have a tough time exceeding the safety and performance of manufactured heaters.

I had a chance to test the shut-down on our Big Buddy and it works well. We have an awning we erect to enclose the rear of our 80, which is equipped with a sleeper conversion. When we camp at the same spot for several days, I eventually have to start the truck to recharge the batteries. The exhaust on the 80 is situated so it pumps right into the awning area, so we usually open it's flaps to let the poisonous fumes escape while we wait safely outside. One time I did it I left the Big Buddy running with the flaps closed. The sensor in it shut the Big Buddy down in short order. I don't intend to test it with humans, but it satisfied me it'll do what it says and keep you safe.

It seems to me you'd want to duplicate that feature somehow so it will work equally reliably if you build it...

OK, now I think I have a constructive suggestion. Build a metal box big enough to hold whatever Buddy you think suits your needs, with a suitable lid, etc. Make sure there's a good amount of clearance on the side that the heat element faces. Use the blower you have and run a return duct from the tent to the box and a heat duct leading back, with the fan installed to push air through. That gives you the advantage of relying on the proven control circuit of the Mr. Heater, in the form factor of the Zodi. No need to fiddle with the complexities of a heat exchanger, just simple sheet metal work.

 

[Skylo]

I also use Mr.Heater and although the safety features are great a bought a cheap (under$10) carbon dioxide/monoxide sensor with alarm.The heater sits on a fire proof mat in the tent.I feel a lot of things will have to go wrong to be a danger now.