It was such a simple project; replace the old cast iron boiler with a new condensing boiler. You knocked it out in a few days. Then, the phone calls started. We’ve all had those projects that both haunted and cost us. The following are some ways to limit those projects.



The new condensing boiler will most likely vent through the sidewall of the house. No problem, drill two 3-inch holes, and you are ready to go. This is one of the most critical parts of the project and should never be overlooked. 

When looking at installing a boiler which vents horizontally out the wall using PVC, I think about what a mentor said PVC stood for: “Pipe Very Carefully.” This is more evident when working in an older home. The following are the rules for horizontal terminations, as published in the International Fuel Gas Code, section 804:

  • Where located adjacent to walkways, the termination of mechanical draft systems shall not be less than 7 feet above the level of the walkway;
  • The vent system shall terminate not less than 3 feet above any forced air inlet located within 10 feet; 
  • The vent system shall terminate not less than 4 feet below, 4 feet horizontally from or 1 foot above any door, window or gravity inlet into the building; 
  • The vent termination shall not be located closer than 3 feet to an interior corner formed by two walls perpendicular to each other; 
  • The vent termination shall not be mounted directly above or within 3 feet horizontally from an oil tank vent or gas meter; and 
  • The bottom of the vent termination shall be located not less than 12 inches above finished grade. 

Your window of opportunity for properly venting the new boiler is quickly narrowing. What the code does not cover is, what is directly below the vent termination? Is it a favorite bush or garden? If so, the acids from the condensing flue gases can destroy any plants below and around the termination point. 



The other consideration when sidewall venting the new boiler is what do you do with the water heater vent? This is called an orphan. I know what you are thinking, I am just there to replace the boiler. If you ignore the orphaned water heater, you will most definitely get a call sometime in the future, and it could be an expensive call. 

When leaving an old water heater flue in the chimney, the flue gases for the water heater will condense because the chimney is much larger than required for one water heater. The Seven Times Rule now comes into play. The seven times rule states the common flue cannot be larger than seven times the area of the smallest flue. 

For example, the existing chimney is 12 inches by 12 inches, making the internal area 144 inches. The existing flue for the water heater is 4 inches. The area of a 4-inch flue is 12.56 inches. If you multiply 12.56 by 7, you would see the largest area you can use is 87.92 inches. This is well below the 144-inch area of the existing chimney. 

In this case, the water heater would require a chimney liner or sidewall venting. Wondering how you will compete with the low bid contractor for this project? I would suggest making copies of the International Fuel Gas Code and show it to the customer. You now become the expert. 



When talking with owners about replacing their old boiler with a new condensing boiler, I explain how the new boiler will require more maintenance than the old boiler. On the old boiler with the standing pilot, most homeowners rarely did maintenance, and the only time a service technician saw the boiler was when it stopped working. 

One of the common complaints I hear when talking with customers is, they never knew about the maintenance the new boiler required. I use it as a sales benefit. Make it something the customer understands. 

In my locale, we have about 4,000 heating hours a year. I like using a vehicle metaphor when discussing the boiler maintenance. I have the customer imagine their car running for 4,000 hours at an average speed of 25 miles per hour. At the end of the 4,000 hours, the vehicle would have roughly 100,000 miles. During that time, the owner would likely have 33 oil changes, four new tires and new brakes, at a minimum. 

I compare that with the times it takes to do the boiler maintenance, and the boiler seems like a deal. You could include the maintenance in your price because the other guy will not even mention it. 


Parts availability

We replaced a 30-year-old boiler with a new condensing boiler for a neighbor. The salesperson told us this was a brand-new boiler, and it was terrific. What the salesperson forgot to mention was they did not stock many parts for the boiler. 

The owner loved the new radiant heating system and the lower fuel costs. The system worked great for about two months. On an unusually cold Friday, the owner called and said the boiler stopped working. Our technician diagnosed the problem as a defective inducer motor. 

I drove to the wholesale house to pick one up. The person working the counter told me it was not in stock, and they could have it Monday. Asking what the customer should do for heat, the counter person shrugged his shoulders and walked away, which really angered me. 

Luckily, the home had a fireplace, and they lit it, and we dropped some portable heaters off at the house. The customer was able to shiver through the weekend, and we replaced it Monday. 

I learned a lesson that day. Two lessons actually; never be the Beta tester for new technology, and only sell equipment when they have plenty of parts. 

I hope this helps you avoid hassles on your next condensing boiler project and the only calls you get are from happy customers.