---
title: 'Heating a Bathtub with a Pile of S#*t | Shut It Off ASAP'
source: 'https://youtube.com/watch?v=yZIl919ClFo'
video_id: 'yZIl919ClFo'
date: 2026-09-09
duration_sec: 1183
channel: 'AsapSCIENCE'
---

# Heating a Bathtub with a Pile of S#*t | Shut It Off ASAP

> Source: [Heating a Bathtub with a Pile of S#*t | Shut It Off ASAP](https://youtube.com/watch?v=yZIl919ClFo)

## Summary

In this episode of 'Shut It Off ASAP', the team builds a solar-powered composting toilet to manage their production's organic waste and uses the heat generated from the compost pile to heat a hot tub. The video explores the science of composting, the environmental impact of waste, and the potential of humanure as a fertilizer, culminating in a relaxing soak in a hot tub heated entirely by their own waste.

### Key Points

- **The Challenge** [00:05] — The team faces the challenge of managing organic waste from their production and decides to build a solar composting toilet to create fertilizer and heat a hot tub.
- **Global Waste Problem** [01:15] — 290 billion kilograms of feces are produced every year, highlighting the scale of the waste problem and the potential for harnessing it as a resource.
- **Composting Science** [03:26] — Composting is an aerobic process where bacteria break down organic matter, producing heat, carbon dioxide, and water, unlike anaerobic decomposition which creates harmful methane and hydrogen sulfide.
- **Historical Waste Management** [04:46] — Domestic wastewater has been used for irrigation since 3200-1100 BC, and the city of Lothal in India had a sewer network around 2350 BC, showing that waste management is an ancient practice.
- **Phosphorus and Humanure** [07:25] — About 2/3 of the phosphorus we eat passes through us, and the phosphorus available from urine is approximately 22% of the total global phosphorus demand. Mining phosphate is energy-intensive, and peak phosphorus supply is estimated by 2033.
- **Food Waste and Methane** [09:50] — Around 17% of all food is wasted annually, and when it ends up in landfills, it produces methane, a greenhouse gas 28-36 times more effective at trapping heat than CO2.
- **Compost Temperature Management** [10:36] — The compost pile temperature spikes in the first few days; if it gets too hot, it can kill beneficial microbes, so it needs to be turned to cool down and reintroduce oxygen. High temperatures also kill pathogens.
- **Composting Timeline** [15:03] — The compost needs to be pulled out every 2-3 weeks and then composted for over a year before it is safe to use on trees and shrubs, ensuring pathogens are killed.
- **Hot Tub Success** [16:16] — The compost pile heated the hot tub to 150 degrees Fahrenheit, exceeding their goal of 103-104 degrees, proving the concept works.
- **Waste as a Resource** [18:09] — The episode concludes with the realization that waste is not just garbage but a valuable resource that can be composted to return nutrients to the environment, emphasizing the need to 'stop wasting waste'.

### Conclusion

The episode demonstrates that with simple science and a bit of creativity, human waste can be transformed into a valuable resource, providing both fertilizer and heat. It challenges viewers to rethink their perception of waste and consider the potential of composting in reducing environmental impact.

## Transcript

This is a giant pile of crap made of animal poo and all of our organic waste. And I'm building a toilet that will use the sun to compost our waste.
Oh, my God, it's hot! Ahh! My God, y'all are gonna have to turn the cameras off while we have a romance!
All of this garbage right here is from the entire production over the last week, really hard to have an eco-friendly production. But this episode, we are shutting off our waste
But it also means we don't know what we're going to be doing with the waste from our bodies. It's one of those things that you don't often think about,
but this week, we're going to be dealing with it. So we're going to shut this and figure out a plan. 290 billion kilograms of feces every year.
So I'm going to figure out how we're going to be harnessing that stuff to create fertilizer. - Okay. - So we're going to be building a solar composting toilet that we're going to be using to create a fertilizer
I have decided to try and deal with our organic waste. but my idea is to use the heat that comes from compost
so that after all of this we can relax in a nice bath. We have picked the hottest day to be building this toilet,
this solar toilet that the farm is going to be using after this. This is our gift to them-- the place where you take a dump. This little bit coming out of the back is going to be where
that's going to act like a greenhouse to heat it up. that's going to be taking out the moisture and the heat. - Okay. Good luck. - But we shall see.
but since this is my first time building one, and have the smell coming right back into the bunky. I'm here with Dave, who works on the farm,
do our composting mission to heat our hot tub. We'll come back to that in a bit. I've build a few piles, and I love compost.
Have you ever built one that heated a hot tub? Um, I'm very curious to see the outcome.
So we've already pre-built this. The composting process is an aerobic process, - That's for the bacteria, right? - For the bacteria.
because it's not going to smell very good. bacteria produce oxygen-free sulfur, nitrogen, and carbon byproducts like hydrogen sulfide and ammonia,
and methane, a horrible greenhouse gas. nitrates, carbon dioxide, but not nearly as bad, and water.
before we build the pile is put these T-posts in. - Okay. - And we're going to use those to support the pile. Do I need my hands here or--
- Okay. - All right? And I think that should be far enough down. That looks pretty good. Can you see the bubble?
So we've got the frame of our crapper up. That's why there's three straight men with me right now. - Straight. - And now we can put on the roof.
Up until that point, things we would look at as toilets Domestic wastewater used for irrigation
has been used since 3200 to 1100 BC. The city of Lothal around 2350 BC in Gujarat, India connected to a covered brick and mortar sewer network
that emptied either into the surrounding water bodies or into cesspits, The 11th century castle building room had chamber pots, actually integrated into the architecture.
so for now when nature calls, And it's just a pee-pee! They're going to grow deliciously tall from this.
lots of things in there to feed the microbes. I borrowed this trough from the farm. and our goal is to get that water
because that's the perfect temperature for a hot tub. Our most important ingredient perhaps is our big pile of poo. a source of heat and food for our bacteria,
Just like humans with food or even cars with gas, in an exothermic reaction, meaning it releases energy.
that the crew and Greg and I have been making during this show, to feed those bacteria so they make as much heat as possible.
and now there's a structure. It's kind of beautiful. with our feces and our urine comes next. So I'm just enjoying the pristine smell of plywood.
So I'm here with Antonio, who taught me about solar toilets, because I used yours. We don't need to go into any more details than that. I need your help. You are the solar toilet king in my opinion.
I don't think a lot of people even know that about me, so... So we are actually going to be using our humanure So why is our waste, which to me feels so disgusting, like, good for trees?
Everything is a closed cycle, so humanure is really good because if you eat good food, then it's loaded with really good nutrients. all the things that these like, chemical companies are selling us fertilizer.
We humans need phosphorous, too. It forms a scaffolding of our DNA. It's a key element in our tooth and bone minerals.
But most of the phosphorus that we eat actually passes through us untouched. Depending on diet, about 2/3 of our phosphorus winds up in our urine, The phosphorus available from our urine is approximately
22% of the total global phosphorus demand. Mining phosphate to make phosphorus fertilizer is energy intensive Experts also estimate that the peak supply of phosphorus will be reached by 2033.
save the environment, and reduce the cost of food. - so that there's already something there. - Yeah, yeah.
That's not right. That's not right. - It's cleaner. It's like-- - These are things you need to think about. all you got to do is cover it up with the woodchips,
So the sun comes in. Heats up everything, So it gets really hot, and because it's airtight, that moisture goes in the air,
- With the solar-powered fans. - Yeah, the solar-powered fan. The humanure becomes safer as you remove that moisture, and it doesn't smell. So I'm going to pretend this is full of crap
Wheeling out the crap! Now that the foundation and structure are in place for our hot tub build, Copper is an excellent heat conductor,
in contact with the hot compost I guess it's just a matter of putting our compost on top of this now? - We'll put our ingredients to make our compost on top. - Okay. Right, I see.
- It's compost once it's all broken down by our microbes? - That's right. Yeah. rotting vegetables, and straw. Around 17% of all food gets wasted every year,
Instead, most end up in landfills trapping heat in our atmosphere 28-36 times more effectively than CO2.
the waste cannot be properly broken down by microbes, which can seep into the surrounding area But our compost pile will minimize these negative effects.
that have high levels of carbon between our green materials, like organic waste and manure that are rich in nitrogen, Generally, what you'll see is the temperature will spike in those first few days.
- Oh, because it's too hot. Oh, my God. - Because it gets way too hot. so many little tiny metabolisms, - Okay. - Once the microbes get to work,
and in the process release heat, But we want to keep an eye on this temperature. we risk killing the beneficial microbes,
This will cool it down and introduce more oxygen again, Those high temperatures also kill off any pathogens, So if we build this pile all the way to the top,
- and it would be about half the size. - Are you serious? At the end of the decomposition process, the microbes ultimately create compost.
which improves soil structure, pH, and nutrient content, and is prized by gardeners and farmers for growing crops and keeping soil healthy. - All right, more poo? - Yeah, let's go a little bit more poo.
It's messy. It's stinky, but I am having fun. and just hoping I don't have to get too much into the poop, This is when the gloves come in handy.
Now we're creating a greenhouse effect. - Both: On the top. - 'Kay. to help the flow of air go up to the roof.
- True. True. - Antonio's great. and a great asset for us to understand how simple this solar toilet is Turning it into humanure is so practical, it's fascinating,
because sometimes I'm like, this is too good to be true. so what happens when it rains or it's at night? You don't poo? Because  you add all those woodchips, it sucks up moisture, and then when the sun is out,
- So at night or when it rains, it's fine. - Oh. The compost pile is taking shape - It's getting bigger. - I'm really happy with the layers that we're doing.
From the outside in, it definitely looks disgusting, I'm wondering what you think the sort of main advantage of composting is.
and send a lot of it off-farm to people's kitchen. we need to put at least an equivalent amount back in. That makes sense, because just the act of growing stuff is using those nutrients.
And once we're finished adding our layers, while avoiding damage to the copper coil While I am exhausted and I am sweating,
and that's making me really excited. Hopefully we have a hot tub. It's so good. Amazing. I'm so glad we have this.
- Can we use it? - We can use it. It is ready to go. - Is there a creature in here? - So this is the sawdust. Get my saw sawdust, put it in my bag.
I like to be sitting down so it could be either for me. - You put it on top like so. - Ooh. the amount of moisture and decrease the smell.
I want to look in here. - Oh, my God. - Ooh! Hello! Wait, I want to know what all that does.
- It's like a little greenhouse! - It literally is a greenhouse. is going to be getting all the smell and all the moisture out of this system. when you pull it out every 2 to 3 weeks.
And then this you take to a part of the farm where you'll be composting it. It'll take over a year before you can use it on trees and shrubs. before we can be confident the process has killed off the pathogens.
because although it's rich in healthy nutrients, However, it's perfectly safe for trees and shrubs.
- Potassium. Phosphate. It's all in there! - It's very cool. I just can't wait though till I'm pulling it out and being like, "Oh." We can finally go to the washroom more comfortably,
I went to number two last night at 2:30 AM Should you give it a little christening? Do a test? - Oh, my gosh. - See you later folks!
Oh, God. I don't know him. After a few days of waiting, we are finally ready to enjoy our hot tub.
- First of all, can you not feel heat radiating? - Oh, my God! It's hot! The thermometer in there is reading 150 degrees Fahrenheit, temperature of our poop and our organic waste pile.
Our goal was to get around 103, 104 Fahrenheit, We haven't been able to look since we insulated it, - See where we're at. Okay, will you help me? - Yeah.
Let's see. Ooh! It's warm. That is higher than we actually were anticipating. - That's hot garbage water. - I have one more surprise for you,
While everyone watches as I blush? 'Kay, these are gorgeous, I will say. This is so much more beautiful than me just making a toilet.
( smooth jazz playing ) It's an outdoor bath. I'm obsessed.
- Aah! - Ooh. - No, it's not. - This is from hot garbage? - Oh, my gosh, Mitch. - ...heating the water.
- This is so cool. - Isn't it crazy? And can you believe that that pile of poo doesn't stink right behind us? - I love these flowers, too. - Me, too.
Now this is off-grid living. This whole experience with waste was, you know, a little smelly at times, a little gross, but I think a lot of it is context.
You realize, is it really waste if it's used in another way? So what's fascinating for me is that this toilet, it doesn't use any water, we've evolved to be disgusted by it to stay safe.
But when there's so much potential Obviously the hot tub is not the most practical version, but it was really fun way to show a principle of untapped resources,
or maybe communities can take their garbage and compost it. And the end result is this nutrient-rich beautiful compost that can be used to re-introduce nutrients back into our environment.
At the end of the day, we need to stop wasting waste. Not only minimize our waste, but actually use the stuff we are creating. This episode did make me realize that waste is beautiful.
That is such a good line, Mitchell Moffit. - Like, the whole series. - ...that was so stressful. In a hot tub, spa vibes with a pile of poo.
- Very relaxing. - Continually absurd. I don't want to get out. It's going to be the hardest part, because it's so warm. - Well, let's just stay in. - I can't believe this build.
( Mitch laughs )