It’s not every day that I learn something new that is HVAC-related by reading the local newspaper. But recently, while kicking back on a Sunday morning enjoying a cup of hot coffee and a tasty toasted bagel and cream cheese, I read an article in the Cleveland Plain Dealer that made me sit up and take notice. The article talked about using sewage as a source for geothermal energy.

After the coughing spasm died down and I was able to swallow a bit of the coffee to wash the phantom bad taste out of my mouth, I read about a Philadelphia-based company, NovaThermal Energy LLC (, that uses technology patented in China to extract useful heat from the rivers of waste water that flow under our streets .


Except, when you think about it, doesn’t this make all the sense in the world? Human beings produce lots of waste water — so much that there apparently isn’t a reliable source as to what the actual number is, though some Internet sources guess that it’s around 20,000 gallons per year per person. Oh my!

Apparently this technology is being used in two projects in the Philadelphia area ( and there are a number of other projects in the works.

The Plain Dealer article quotes company CEO Elinor Haider as saying NovaThermal Energy plans to market this technology to any large commercial (100,000 sq.ft. and larger) building located on or near a major sewer trunk line that contains a steady flow of wastewater.

OK, so what’s the deal here? How does this work, and aren’t there concerns about health and safety?

It works like this: Heat is produced by bacteria in the sewer water that heats up as it breaks down. This is a chemical reaction similar to what you’d see in a compost pile in your back yard. Add to that the fact that there’s a lot of hot water in sewer lines from residential showers, dishwashers, and washing machines, as well as hot waste waters from industrial processes. Talk about a primordial soup.

According to the NovaThermal Energy website, this water temperature is about 60F in the winter and 75F in the summer.

Any conventional heat pump can transfer that heat to clean water pipes, while keeping the clean water and wastewater separated at all times. But here’s the rub — until recently, solid matter that’s in suspension in the wastewater would clog up a traditional heat pump and prevent it from working. Imagine how fun the job of cleaning that out would be from a service technician’s viewpoint.

According to the article in the Plain Dealer, a Chinese company called Jin Da Di invented what they call an anti-block machine to filter this solid matter out before the water enters the heat exchanger. The solid waste is then returned to the sewer system. A website called Sustainable Future, Green Homes, does a nice job of outlining more of the technical aspects of how this system works. Just point your browser to:

So what’s missing? Well, there’s no well drilling necessary, no earth trenching required. There’s no need to drop pipe or repair landscaping. How much do you suppose that impacts the first cost of this system?

And if that doesn’t make you take notice, think about this: A commercial building owner can replace refrigerant chemicals with hot and cold water. What are the long-term ramifications of that?

Is it efficient? According to a quote from Haider, it’s more efficient than traditional geothermal heat pump systems. Since the Philadelphia projects are new, we’ll have to wait and see if that pans out.

I suppose the only downside could be viewed as the smell. And even that isn’t a factor unless there is a leak and that applies whether you’re using a wastewater geothermal system or not. I also suppose those sensitive to the matter will say this isn’t green technology, it’s brown.

But everyone is color blind when it comes to saving money, and according to the NovaThermal website, this technology can save building owners up to 60% in HVAC costs.

Now doesn’t that help you overcome the "yuck" factor?