How to Look

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We want you to be an informed homebuyer, and each blog post is a question that we have answered for our friends and customers over the years. Hope they help you make a good choice for your next home.

    There are charts that list the maximum length of a trap arm for each pipe diameter. A trap arm of 2” pipe at a 1/4” slope, for example, is listed at 8 feet maximum length. It is not a coincidence that 8 times 1/4” equals the 2” diameter of the pipe. That’s because there has to be a continuous channel of air between the trap and the vent, or else trapped air in the drain fluid will cause a vacuum that sucks the trap dry and allows sewer gas to enter the home. The same scientific vacuum principle that is used to siphon water out of a fish tank comes into play when the top of the inside of the pipe descends below the level of the trap weir.


    The trap arm length tables always include a note that states that “the vent connection shall not be below the trap weir,” and that is the overriding standard to follow when calculating maximum slope of a trap arm. So the trap arm at the laundry sink shown above definitely exceeds the maximum slope for its length.


While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
© McGarry and Madsen Inspection

 


More Blogs about Plumbing:

  1. So the water heater is older...what’s the big deal?

  2. When is a water heater drain pan required?

  3. Does a tankless water heater require a pressure relief valve?

  4. Why is there water in my water heater drain pan?

  5. What are the most common installation problems with water heater replacement?

  6. Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?

  7. What can I do to make my water heater last longer?

  8. How much does it cost to replace the water heater?

  9. Why do water heaters have a sacrificial anode?

  10. Should I upgrade to a tankless water heater?

  11. How much does it cost to replace the plumbing in a house?

  12. How old is that water heater?

  13. Why is spray foam used for attic insulation?

  14. How do I get rid of the sewer gas smell in my house?

  15. What causes low water pressure in a house?

  16. What’s the powdery crust on the pipe connections at the water heater?

  17. Do you check the plumbing under the floor slab?

  18. What is a “cross connection” in a home’s plumbing system?

  19. What’s the flip-up handle on the water heater for?

  20. What is the difference between water service pipe and water supply pipe?

  21. My well water test came back positive for bacteria. What should I do?

  22. Do you test the well water?

  23. How can I tell what type of plumbing pipe I have?

  24. What is the difference between a regular water heater and a power vent water heater?

  25. How can I determine the age of a water heater if the serial number is missing or decoding it is impossible?

  26. What is a saddle valve?

  27. How do you test a shower pan for leaks?

  28. What is a grinder pump?

  29. What is that little tank on top of the water heater for?

  30. What is a galvanized nipple?

  31. What are the minimum clearances around a toilet?

  32. What is the average lifespan of a water heater?

  33. What are the most common plumbing problems with older houses?

  34. Why are rubber washing machine hoses a safety risk?

  35. What is a dielectric union?

  36. What is a heat pump water heater?

  37. What are the common problems to look for when the plumbing has been replaced in a house?

  38. What is the average life expectancy of copper pipe?

  39. Why can’t PVC pipe be used for water pipe inside a house?

  40. What is the average life expectancy of PVC pipe?

  41. What is an auto vent, air admittance valve, or check vent?

  42. Why is a European-style bottle trap not approved by the plumbing codes in the U.S.?

  43. What is the average life expectancy of CPVC pipe?

  44. What is an FVIR water heater?

  45. Why is sunlight exposure bad for PVC pipe?

  46. What is the loose wire sticking out of the ground under the gas meter for?

  47. How can I locate my septic tank?

  48. Why is a backflow preventer required on lawn sprinkler systems?

  49. What are the right words for talking about a house plumbing system?

  50. Should I seal the washing machine drain hose to the standpipe?

  51. How can I tell if a house is connected to a septic tank or sewer?

  52. What is a sediment trap or dirt leg?

  53. What is the purpose of a thermostatic mixing valve above a water heater?