GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Chimney liner needed when converting from tank to tankless water heater?

philliphcgroup | Posted in Mechanicals on

I am planning to have a tankless water heater installed (not looking for full payback just want continuous water, more floor space, and less natural gas consumption).

I had a couple mechanical contractors come out today to give bids. One mentioned that if I convert to a tankless water heater that I will need to have the chimney lined for my furnace vent pipe. He stated that since they will be removing the vent in the chimney that is for the current water heater, that the furnace will need a liner now to eliminate condensation.

The other guy that came to give a bid never mentioned anything about a liner.

Do I really need a liner in my chimney because I am getting rid of a tank water heater? Eventually my furnace will need upgraded and the chimney venting will be eliminated all together because of the direct venting in current furnaces. If I don’t need to get it lined I’d prefer not to spend the money.

Thanks in advance for the comments.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. davidmeiland | | #1

    Sounds like the two appliances are vented together at the moment. The usual problem is that the furnace is replaced first, and the water heater is "orphaned" with a chimney that's too big, so it drafts poorly and may have condensation problems. You're removing the water heater first, and the flue size should be evaluated as to whether or not it's suitable for the furnace alone. I would look at the furnace installation manual to see if that tells you what the requirements are, or contact the manufacturer with a description of the chimney and get their feedback. I like bidder #1 for the fact that he recognized the possible issue.

    Is this a brick chimney that starts in the basement, or what?

  2. philliphcgroup | | #2

    Thanks David. Yes this is a brick chimney that originates in the basement area. Not sure I will be able to find the manual. I actually have a furnace guy coming this week to do PM on the furnace so I was going to ask his opinion as well. I was just looking for some other's comments as well. Thanks.

  3. GBA Editor
    Martin Holladay | | #3

    David has give you good advice. For more information on these issues, see When a Flue is Too Big.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |