Let’s keep the momentum. Let’s rant some more about green stuff.

The old sewer clay tiles need replacing; that decision has been made. But what material should the new sewer be made of?

This decision is made for us, and the answer is given in the Chicago plumbing code. All concealed (i.e. buried) sanitary sewers within a building must be cast iron soil pipe (CISP).

Iron? For waste water? In soil? Wow – wait a minute. This doesn’t make sense! Isn’t iron subject to corrosion? It may rust from the inside and outside. We are using low flow and low flush systems, which reduces the dilution of any acid based liquids (such as urine) and increases the probability of corrosion within a cast iron sewer pipe.

We will use a high efficiency condensing boiler. The condensate from such a boiler is known to be corrosive and further increases the probability of corrosion within a CISP. What about the longevity of this thing? Once I am done replacing it, I never want to touch it again, even if I get to be a 100 years old!

CISP Institute information proceeds to inform me that cast iron pipe are highly durable and probably the best material to use. Well, this is sort of expected. But I still have a hard time believing that CISP is as corrosion resistant as HDPE (high density polyethylene) or PVC (polyvinyl chloride) piping. Resistance of HDPE pipes is rated from pH 1.5 to pH 14, according to a sales representative. So maybe I need to take this with a grain of salt too!

Because HDPE or PVC pipes have good corrosion resistance, they also maintain good flow and slide characteristics, which in turn reduce maintenance or blockage compared to CISP’s.

And there is the carbon footprint issue. Wouldn’t you expect cast iron to have a much larger carbon footprint compared to HDPE or PVC? Time to find out.

The International Centre for the Environment (ICE) at the University of Bath (England) has published the ‘Inventory of Carbon & Energy’ for various building materials. I found data for all three materials (cast HDPE, PVC and iron) and was able to calculate the following carbon footprint per linear foot of a 4 inch sewer:

Even though the cast iron sewer has the biggest carbon footprint, the CISP Institute points to the recycled content of the product and labels it green (see page 131 of the CISP and Fittings Handbook).

PVC is a distant second, but is no angel. The production of polyvinyl chloride has all sorts of environmental issues associated with it. PVC piping (such as Schedule 40) is very popular though because of its low cost and ease of installation.

HDPE appears to have the lowest carbon footprint out of the three materials. It seems to have a better reputation than PVC with regard to environmental issues and is recyclable. It is more difficult to install compared to PVC and requires fusion or welding equipment for moist pipe joints.

Thinking this all through, and assuming that I have my facts straight, I really would like to use HDPE piping for the sewer replacement.