Switching from electric tank to gas tankless questions.

Discussion in 'Tankless Water Heater Forum' started by Chad Sethman, Feb 3, 2019.

  1. Chad Sethman

    Chad Sethman Chad

    Feb 3, 2019
    Hi there,

    I have noticed some post that have provided me with good information but I thought I would make my own post to more specifically address my questions. I have an outdated electric tank water heater and I am considering switching to a super high efficiency (condensing) natural gas tankless heater. I have an area in my cement block basement near my existing heater that has gas and water supply nearby. There is a glass block window directly above where I would want to mount the heater. I was thinking that I could vent the heater by knocking out one of the blocks. The blocks are 8". Would knocking out one block be sufficient or would I have to knock out 4 blocks (any advice on removing these blocks is appreciated). Currently there is a 1" gas supply line right to the area, there is a 2" line about 10' away. Is the 1" line sufficient? The 2" line splits to two 1" lines, one going to a canning stove and the other 1" line would go to the water heater. Also, would it be easier to anchor the unit directly to the block or would it be easier to attach some 2x4s to the wall first then anchor the heater to these. Ideally I would like to do as much work myself and at least prepare the gas and water supply lines to the area, prepare the vent route and mount the water heater to save money. I understand the warranties are sometimes void if it isn't professionally installed, I would think my DIY extent would be fine as long as a professional actually connected the lines and vent. Does this all sound feasible? Any advice would be appreciated. Thanks!
  2. Dana

    Dana In the trades

    Jan 14, 2009
    A gas tankless usually needs a dedicated "home run" line tapping in as close as possible to the meter/regulator as possible. Otherwise the pressure fluctuations when other large gas loads start or stop can interfere with the operation of the modulating burner in the water heater.

    The line has to be big enough to handle the total BTU/hr at maximum fire. For most 199,000 BTU/hr tankless units it will be 1-1/4" minimum unless the tankless is VERY close to the regulator.


    The lengths in the chart include adding in the "equivalent length" of every ell, tee, and valve along the path, not just the straight pipe sections.

    With a condensing tankless you don't need to knock out a whole block to accommodate the plastic venting & combustion air pipes. Drilling it out with a hammerdrill is usually better, less likely to start a crack in the foundation.

    A non-condensing tankless usualy requires stainless venting, making a condensing tankless cheaper to install despite the higher price for the unit itself.

    Consult the manufacturer's instructions on how to mount it to a CMU wall.
    Last edited: Feb 4, 2019
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  4. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    Some gas utilities will deliver 2 psi, instead of the common 1/4 psi, to a residence, and then each gas appliance made for 1/4 psi will have its own regulator. This makes the same pipes deliver much more gas energy.

    If this is an option, you could consider converting. I checked https://www.columbiagaspa.com/ but I did not find this mentioned.
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