Some Frat guys at another tailgate had a truck bed full of cold water... They thought they were the smartest guys in the world. So I decided I could out do the Frat guys. Being that I live in Montana and the weather dips well below the 20's in November I had a challenge. I started acquiring parts from all over the place. I got a 150 gallon stock tank from a buddy out in Minnesota when I went to his wedding. It measured 4ft Diameter and 2 Ft deep. It fit about 3 people comfortably and 6 uncomfortably!! We used this small hot tub the first year and upgraded this last season for a 9ft Diameter hot tub! Go big or go home! Enjoy!
My interview with the news station.
Step 1: Find a Trailer and Suitable Tank
The tank is a cattle stock tank. We had maybe 750 gallons in it. Don't over fill it or else it will overflow everywhere when people get in it. We had to ratchet strap it down with lots of straps. And to prevent to much sloshing during transportation we had to strap a few boards onto the front and back.
Step 2: Insulation Is Key!
We lined the top of the trailer with two inch thick foam boards. Make sure everything fits snug underneath. The weight of the hot tub and a big enough gap could lead to a crack in your tank
The 1x2 foot strips of foam we lined the outer edge of the hot tub with. We ran a ratchet strap around them to hold them in place.
We also added some fiberglass insulation in a plastic sleeve around the bottom as well.
The half circle is actually 2 half circles of 3/4 inch foam board. This made an 8 foot Diameter circle. We laid this on top of the water to insulate it. In the end we actually threw all the extra foam we had on top to help insulate.
Insulate All PIPES!!!
Sorry there isn't a lot of pics... I decided to make this instructable 3 months after the project was over.
Step 3: Pump and Heat Exchange
Key thing with the pump!!!! Always push water through your heat exchanger never suck through it. The water can get ridiculously hot sometimes.
Insulate everything as well. All pipes and hoses should get insulated. The more the merrier!
The BBQ grill I picked up on the side of the road for free. It really is amazing the stuff you find on the side of the road in a college town. I had to weld the hinges cause the bolts were loose but rusted tight. I also welded a few chunks of angle Iron in to raise and strengthen the grill. If you are going to run Charcoal make sure you have a lot of airflow. You don't want to kill the fire buy using a gas grill. And gas grills don't work... Tried it the first year. It was very slow at the heat exchange.
There is 75 feet of 1/2 inch soft copper tubing in this grill. I used a pot to slowly wrap the copper around. Careful when doing this!!! Soft Copper likes to kink. Run the copper out far enough from your grill so you don't melt whatever is attached to it.
Turn your pump on first then, Fill the grill with Charcoal and set it ablaze!
Step 4: Sit Back and Relax!
It took about 1 day to raise the temperature from tap temp which was around 40 to 107.
The temperature outside while this was heating up never went above 36. So I would say things went fairly well!
****I would like to caution you as well to not stop the pump. We had an accident and cracked the inlet line. had to shut the pump down for a good 5 minutes. When we turned it back on it flash boiled the water for about 15 seconds. And all the copper was constricting with the extreme heat difference. It could also cause a blow out in the copper.
**** Another side note... I feel dumb about this one! When adding charcoal to the hot tub in your swim trunks... Don't slip on the Ice into the 400 deg BBQ... 2nd degree burns to the back! Very painful! Wasn't even that drunk... : )