hotwater venting

Question

I installed a 50 gallon gas hot water heater and i noticed that the red and blue plastic around the hot and cold water pipes is melting. it has a 3 inch vent hood with 3 inch galvinized pipe to the chimney pitched up 1/4 inch .So I took the piping apart to see if anything was blocked and it was clear and I also checked the draft with a match and on the side were the cold pipe is it seemed stronger then were hot water pipe is. I have the same hot water heater as this one and mine is ok . Is there anything that can help me with this problem .Also the heater was set on the highest temperture setting but I don't think that matter .Thanks Ron Tredo

Answer 1

 

Hi Rontredo,

 

You’d have to put quite a few variables into a basket to answer this question, such as:

• chimney flue diameter / height of a chimney
   
• new WH BTU’s, how many (and what type / fuel) appliances venting into the chimney besides the water heater / their BTU’s
   
• type and dimensions of their connectors
   
• did you check the chimney’s entire flue for obstructions or just the water heater’s connector
   
• is the cap in good condition
   
• is the draft hood original (it came with this new WH) or from the previous WH (maybe undersized?)
   
• are there any exhaust fans operating in the house at the same time (kitchen, bathrooms, window fans, whole house fans) which could create negative pressure / back drafting (doesn’t have to be constant)
   
• are there other chimneys with open dampers (i.e. fireplace)
   
• is there a forced air conditioning system’s return port nearby the water heater
   
• is there a sufficient combustion air supply in the water heater containing room?

I understand that you have the same WH and it is working fine and there’s no melting, etc., but even one of the factors might be slightly different and cause this condition. 

 

Also, chimney draft develops / increases with warm exhaust gasses flowing through the connector and the flue. You don’t need much draft for the test, it’s a small flame and very little smoke, however, when the burner ignites at the base of the water heater, the amount of hot exhaust gasses may not be able to immediately vent through the draft hood and the connector into the chimney.

 

Some of it could be spilling on the sides of the draft hood causing melting of the plastic inlet / outlet markers. As soon as a strong draft develops, those spilled exhaust gasses should be sucked back into the draft hood and vented outside. 

 

To cut it short: in a perfectly designed water heater vent system, balanced air pressure inside the home, and sufficient combustion air supply there should be no melting of those plastic markers. The best way to start is answering to all of the questions above and analyzing those answers.

 

You can also visit a few of my posts dedicated to those problems:

http://www.checkthishouse.com/49/water-heater-vent-pipe.html

http://www.checkthishouse.com/1887/gas-water-heater-and-furnace-chimney-flue-sizing.html

http://www.checkthishouse.com/6236/combustion-air-requirements-for-fossil-fuel-burning-appliances.html

http://www.checkthishouse.com/category/house-safety-bottom-line/carbon-monoxide

Just click on “comments” below if you have more questions.