Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Natural Gas Tankless Heater and plumbing

I am a homeowner that has several questions regarding natural gas piping in general and a few specific. First of all we have CSST piping. It would appear that we have 1/2 inch coming up through the wall to the main shut off for the gas. We have an outside regulator. After the shut off there are fittings and a black iron elbow that is fairly large with fittings that goes directly into a 5 PSI regulator -- then almost immediately another black iron elbow -- off of that there is a 3/4 inch CSST pipe that goes directly into the boiler . There is also a T off of that black iron fitting that goes directly into a manifold. Off the manifold are 1/2 inch CSST supplies to a Fireplace, gas cooktop (which I abandoned) and a 40 gallon hot water heater.

I contracted with a company to put in a tankless system. Originally I had a 3 psi regulator and found out after they installed the tankless system it was undersized. They came back and put in a 5 psi regulator The regulator is big enough on the outlet side for all the attached appliances at full load.

I do not really understand any of this but I was told that

1. You cannot go from a 1/2 inch line o a 3/4 inch line -- is that true?

2 The book for the tankless heater says a 3/4 line is needed -- can it run on 1/2 line. It seems to be working (producing hot water) but I am not sure if it will start to malfunction .

3. Also I was told that at least 10 inches of straight pipe needs to be on either side of the psi regulator before the elbow. Every single picture of the installation of a regulator I saw on the internet did have straight pipe. I am being told by the builder that it is not true or necessary.

From the outside regulator to where all this stuff sits (up on the second floor) is a fairly long way up. I have no idea how much CSST there is or how it run because it is behind walls.

There are absolutely NO inspections by the utility company, by the county or any other agency. If the plumber does not do the proper job you have no way of knowing except by researching and hopefully nice people in the know respond.

I am very concerned that this was not done correctly. I just need some idea of what the implications might be.

The boiler -- a high efficiency boiler called a Munchkin is what we have.

All seems to be working but I am concered that there could be potential problems.

Any help would be so very very much appreciated. Just remember to not use super technical terms as I would not understand it. I am still trying to understand the difference between Water Column and PSI!

Thanks again -- I have attached a picture of the lines. Hope this helps


  • Zman
    Zman Member Posts: 7,435

    You are correct to be suspicious. What your plumber is doing is running an undersized line at high pressure. Then he is regulating it back down at the appliance. If you have the btu rating of the appliances and the length of the runs, someone may be willing to help you calc this. In my mind this is crazy. Opinions may vary. 27.7 inches of wc = 1psi

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • RobG
    RobG Member Posts: 1,850
    Gas Piping

    You may have some issues. I would re-post this thread in the gas forum. As well, more info id needed.

    1. gas pipe sizes and lenght of the runs to each appliance from the manifold.

    2. BTU ratings for each appliance.

    The gas piping for your boiler should be a mimimun of 3/4" , maybe larger depending on the lenght of run,

    Also, photos of the piping at the appliances would be helpfull

This discussion has been closed.