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.

Change from 2 water heaters to combi

I live in a 1800 sqft home that has 3bd 2 bath. It has radiant tube in the concrete floor. Currently I have 2 50 gal water heaters. 1 for floor heat and 1 for Dhw. I am think about going to a navien combi boiler. My system has 3 zones with three circulator pumps. Do I need alot of piping changes or just extend from my current water heater to the correct ports on the combi boiler?


    EBEBRATT-Ed Member Posts: 15,839
    The smart thing would be to download the manual for the combi you wan't to install and read the manual which will show a basic piping diagram.

    I would be cautious about which brand combi you select. Some brands are having issues
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,389
    Hi @cwmccoy , I'd also want to get an idea of heat loss for the space heating side of things. What's causing you to look for a change?

    Yours, Larry
  • Ironman
    Ironman Member Posts: 7,399
    edited February 2022
    I’d highly recommend that you look at using a property sized heat only boiler with an indirect water heater for domestic. It will cost more up front, but be more reliable and need much less maintenance in the long run.

    A combi that would be large enough for your domestic load will probably be way oversized for your space heating load. Over sizing greatly reduces the life expectancy of the boiler as does the constant on and off that a combi experiences from short domestic draws.

    Personally, I would avoid a Navien.

    Also, realize that a mod/con boiler requires specialized knowledge and equipment (such as a combustion analyzer) for proper installation and operation. It’s not a typical DIY project.

    I’d recommend that you find a competent hydronic contractor and work with him.

    See if the contractor locator above lists someone near you.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,479
    Its always good to know the load first. I’ll bet a 120 combi would cover your application, most turn down to around 8000 btu/ hr. You will probably pick up 10% or more in fuel efficiency, more if you run condensing mode as much as possible.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jon_blaney
    Jon_blaney Member Posts: 322
    Watch the Mikey Pipes videos on YouTube.