Neal Giffin

Update: It is finished, and i am very happy with the results. Just to give you an idea of the efficiency...the last run i started off with 52 degree water, i ran the water from the faucet through the stove, and into the tub. It took about two hours to fill the tub, then i turned on the pump. About 5 hours later, i had about 120 gal of 101 degree water. It really helped when i addled the smaller tubing, insulation, and enclosure. I hope it works this good when it gets cold!
What should i use on the stove to inhibit rust?? I put some wd40 on it, but it didn't work to well.
Thanks y'all
Neal

Pic of stove

After reading some of your replies, i made some changes, and it is working much better! I have increased my output temp 15 degrees. I filled up the tub with 60 degree water, and it was at 92 after three hours, that was without the shield and insulation.  I replaced the 1/2in copper with 50ft of 3/8, i read on my home brewing forum that the 3/8 has more surface area and would better transfer the heat. The smaller tubing was more pliable, so i was able to tightly wind the tubing along the stack, and closer to the body of the stove. I will report back when i get it finished! Thanks for the help y'all.

Thanks for all the replies! I am thinking at this point that if i cannot get more heat out of the system in its current configuration, i wil probably try and put it into the stove pipe. Wrapping it around the back of the stove seems like it would work a lot better, but bending the tubing to fit the small stove would probably be a challenge!
When i shielded the tubing i tried to tighten it up as much as possible to the stove pipe, but some of it isn't touching the pipe because of the oval shape of the connection of the pipe to the stove. I also compressed the tubing down significantly, then added the shield. I was hoping that the sand would help transfer some more heat, but it didn't appear to help much.
Is it possible that i have too much water flow? I would think that the pump is pushing 2-3 gal/min.
Would it help to open up the coil so it is longer-meaning it runs along more of the stove pipe?
I am definitely going to shorten the lines and insulate them. I also plan to insulate the tub.
Thanks again everyone!

Hello all!
I was recently gifted a wood stove, so i decided to use it to heat a DIY hot tub. After some research, i put it together and i am not impressed with the output! I am trying to heat about 100 gallons, and the water temp is around 50 deg right now. The best i could get was 84 deg of output, which barely heated the tub. i had spurts of energy that spiked the temp to over 100, not sure why! I am using 25 ft of 1/2 in copper tubing wrapped around the stove pipe with a small pump to circulate. Since the stove was hand made by a family member, i do not want to cut or drill into it, so putting the coil inside is not an option. Water flow is pretty high, so. I put a valve on the output side, and that seemed to help. I also shielded the coil, and then filled it with sand. i am thinking that i need to go down to 3/8 copper, and extend it to 50 ft.
Any help would be greatly appreciated!
Thanks!