A few friends and I were BS'ing about alternative energy and we all agreed that the septic systems are a definite source of heat. We think a coil assembly with good insulation and a passive glycol system could be used to give moderate heat to a basement or small area in a home.

Anyone ever heard of such a thing? Better yet, anyone ever seen any active plans to do it?

You're joking right? My sludge tank has a concrete column right up to the ground surface and the lid is only around 2 inches thick and yet the snow does not thaw significantly earlier on the lid than it does on the surrounding ground. I can't believe the energy output by the decomposition could possibly be worth harnessing. Plus, my tank happens to be over 100 feet from my house which would require a pretty fair run to transfer any harvested energy. I dunno - sounds kind of iffy. I wonder what the temperature is in the middle of all that poo? And then if you're a good little citizen you listen to the poop truck guy and pump your system like every other year (Which I DO NOT do. Or is that DO NOT doo?)

Our septic is about 20ft from our house and it significantly melts the snow. There's enough gas pressure built up to pop the lids off the pipes if the holes get plugged, (not that that has anything to do with heat). I'd say there's a reasonable amount of heat in there, but wouldn't begin to start quantifying it in terms of usefully recoverable heat. I would say it could be worth a look though. Get a temperature probe and poke it in your tank.

Well...consider this. A simple pile of horse manure can reach temperatures strong enough to create warm steam when turned over...just stick a fork in an active pile sometime in the winter.
The bacteria is already there, creating heat and methane...why not get a little back?

My main tank before pumping is about 1.5 feet below the soil. Its the first place to melt and it has allowed me to grow region 3 roses in a region 4 area.

Gotta think outside the litter Box D!

My one concern would be that if you extract the heat would you reduce the effectiveness of the septic system? Is the heat truly a by product, or does it actually aid the process?

I believe the heat does keep the process going. You would need to regulate the heat.

But...if the heat generated by the tank normally bleeds off into the soil, you could wrap copper and then insulate to make up for the bleed and still have an effective low yield heat source. I imagine a tank with 6 inch polyfoam around it would be quite toasty. But I need to dig a little deeper because I think the process is more geared towards solid waste than anything else. Every manure based heat source I have seen has a much greater percentage of fiber material as compared to septic tanks.

You're thinking inside though.

Okay - a manure pile is significantly different than a typical septic holding tank. I'd estimate for every solid toilet flush in my house I'm looking at many tens of gallons of both hot and cold water passing through the sludge tank. What effect does that have? Do we also consider recovering the heat from gray water (shower, dishwasher, washing machine, etc.). Wrapping an existing tank in insulation would be a significant expenditure. Copper certainly ain't cheap. How efficiently can we transfer the recovered energy from the source to the sink? How much energy would be expended in transferring that energy?

Funny I don't see this melting effect that others do. Maybe I have less bacteria in my poo? I see some melting but it just doesn't seem very significant.

I'm not saying this isn't worth a look but it seems to me there's a lot of things to consider before one could even show on paper that significant gains might be made with such a scheme. And a ground-up approach as opposed to a retro-fit would of course be way more attractive.

I look forward to seeing where this thread eventually goes. Either way, it's down the toilet.

Edit: Missed your % fiber comment above in my first read.

I don't think that you'd get any useful work out of this. It's low-grade heat at best, and there isn't a lot of it. Take too much out, and the reaction will stop which leads to bigger problems. Take too little and it'll be a waste of money.

It might be better to capture the methane output and burn that. Again, it's not going to be loads, but it, unlike the heat, is worth having as you can easily store it and use it all at once.

I did a little reading last night and found out that the majority of the heat from a standard septic tank is actually contributed by water that was heated inside the home. The actual tank produces small amounts of heat but not enough to make a true difference. Those people who have used crap to heat things have nearly always supplemented them with sawdust or like matter with a high cellulose content. Probably a bit too much trouble for the standard user, but still interesting to think about.

the effectiveness of this house warming measure is dependant on many variables..your hot water heater settings, your diet , etc.

I guess it's a matter of scale. If you had a pig farm, cattle ranch, or a large horse stable, You might be able to realize some benefit. On a small scale I have seen manure digesters in Asia used to recapture some methane for cooking, but this only works where the cost of fuel outstrips human labour costs.

I guess that means D takes cold showers ... ?

A septic tank is mostly anaerobic, while the "steaming pile of poo" is mostly aerobic, which is a much more exothermic reaction. Stick some sort of copper heat exchanger in the middle of a pile of compost and now your talking about getting some heat !

well Dave-ak, you are in alaska where heated septic systems are required because of the freezing climate. maybe the excess pressure is from the surrounding area being frozen.

I don't know about septic heat but i do know about a goat manure hot pile / radiant heat system that works.
A woman named Tasha Tudor who lived in VT she lived like she was in the 18th century wove her own clothing and wrote childrens books. She kept sheep and Nubian goats.
Her son built her a very nice pegged post and beam house and i was taken with the sun space on the south east corner of her home.
Tasha shoveled all of the manure and layered the pile into a hot pile waste needs carbon to feed on and a high urea content to cause the heat transfer.

So they had built a brick enclosure with a slab floor with radiant tubing running in the slab. pumped into the boiler and directly into the radiant heat system. Slicker than snot really. the slab picked up soar gain awiththe added kicker of the goat shat and hay. in the spring during the shoulder season mucking out the hot box meant a fresh layer of compost for the garden. If you haven't made hot piles i recommend finding a friend with goats and in the fall pile up the layers a six inch layer of manuer thenhay or straw then manuer etc pile it three or four feet high then in winter shove a thermometer in the middle of the pile if you built it right it shuld be 120F or more.

Sounds like a neat idea. I know the manure here gets hot enough that it steams even on a hot day. 120F = 49C so more than warm enough to make a difference to the hot water bill!

I'd go with some sort of stainless or copper spikes. Probably a mix, actually. You want to be able to simply shove them into the layer, or at the least simply pull them back out with a tractor/digger so you can turn over the "compost", so some kind of stainless rod with a seamless copper tube running up and down it would work great - robust and heat conductive.