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Boiler Swap

Vandal Member Posts: 2
Would a Navien combi boiler/water heater be an adequate replacement for a Weil McLain GV boiler serving radiant floor heating?  Or is there a better mfg with warranty and customer support? 


  • CMadatMe
    CMadatMe Member Posts: 3,086
    Not A Boiler

    The Navien is not a boiler. I belive the true termonoligy they use is "heating box."

    Do yourself a favor and qet a few options and quotes on a condensing BOILER.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Vandal
    Vandal Member Posts: 2

    Please explain WHY you are against using a Navien, Rinnai, Noritz, ect..... hot water heater to heat water in the floor.   
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Although they LOOK like a wall hung boiler....

    The following information is based upon past experience, and I know that many of the tankless manufacturers have changed their methodology, so your milage may vary.

    Tankless water heaters were designed to have a continuous high rate of flow through them and to raise the water temperature a significant amount. i.e. incoming water at 40 degrees F, and discharge temp of 110 degrees F. with a flow rate of 3 GPM. It is essentially a series coil in a fire box.

    Close loop heating system are typically based on a 20 degree differential in temperature, and flow rates are a variable in most cases, depending upon how many zones are calling. When a tankless is put into these situations, it short cycles. In fact it short cycles so bad, that the heat exchanger never really gets a chance to dry out, and the acidic condensate causes it to become plugged with corrosive byproducts of combustion, then causing a roll out condition, or worse.

    Some of the newer models actually have the ability to modulate their burn rate, but the heat exchanger still has to be a series coil in order to cover the need for the high delta T, so they still have an inherently high pressure drop, and are still subject to short cycling during part load conditions.

    Over the years, I have replaced many tankless water heaters that were (mis) applied as space heating products. As a matter of fact, a large tankless heater manufacturer who use to promote its products as space heating appliances, has removed any reference to space heating and has gone back to doing what they were designed for, that being DHW heating.

    Now, this is not to say that you CAN'T mis apply your own tankless, but some jurisdictions do not allow it. And if you do mis apply it, you will think back to this conversation when trouble starts rearing its ugly head, and you will attempt to kick yourself in the butt, and will end up hurting your back and having to go to the chiropractor to get it fixed :-)

    Not recommended unless specifically designed and warranted for that particular application.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • SpeyFitter
    SpeyFitter Member Posts: 422
    tankless as a boiler

    They are not built as robustly as a boiler with an H (ASME) stamp on the heat exchanger, which must meet certain safety and build quality standards to receive this stamp. They do not carry as sophisticated often incorporated controls that many of the higher quality condensing boilers do. Tankless water heaters often have high pressure drops in their heat exchanger which requires a significantly larger pump than even condensing boilers do. The grades of stainless steel they utilize to build their heat exchangers, often times, are not as high a quality as most condensing boilers; for example many condensing boilers use 316 L, 316 Ti (Viessmann, IBC), or 439 Ti (IBC, triangle tube) for their heat exchangers. I could be wrong, but I thought I read somewhere that Navien used 411 S/S on their heat exchanger, which from some minor metallurgy reading I have done, is quite inferior to that of most condensing boilers in condensing applications.

    From a domestic water heating perspective, tankless water heaters require annual service to flush lime out of the heat exchanger, often times. An indirect hot water tank made out of stainless steel that is heated by the boiler requires very little service in it's lifetime in this regard. Heating an indirect, a condensing boiler will see efficiencies in the 85-90% range due to the higher temp water the boiler must produce to heat the indirect which reduces it's efficiency slightly. But at least when a condensing boiler is heating an indirect it typically has a nice long burner cycle which allows the boiler to get to it's steady state efficiency rating where it is burning quite clean. This also produces less wear and tear on the boilers ignition components, and puts less thermal stress on the heat exchanger over the course of its lifetime. When you look at a tankless water heater heating domestic hot water, the thing typically short cycles all day. Perhaps if you're having a 10 minute shower it'll start to get to it's steady state efficiency, but think of the pulse loads you put on it every day. Every pulse load (washing hands, doing dishes, filling up the laundry machine - some front loads pulse the hot and cold continuously to make a moderated warm temperature) puts wear and tear on the tankless unit's ignition components and prevents it from reaching its steady state efficiency, plus produces more emissions.

    Bottom line - you do get what you pay for.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • StarMan
    StarMan Member Posts: 1
    Navien Combi IS a boiler

    The Navien Combi Boiler is not a tankless water heater. It is a well designed cost effective boiler for radiant heating projects. It differs from their true tankless heater models. It heats the heating side- the radiant water- directly with the gas burners, and it heats the DHW via a S/S flatplate heat exchanger- all built into a very compact unit including boiler pump, buffer tank, water fill valve and outdoor reset control.

    We have used Navien Combi's and the Navien Tankless Water Heater model-A 's with internal recirc pump and minitank, all in heating applications- and they have performed very well right out of the box. What? yes, even the A model can be used for radiant heating, if you connect it using a primary/secondary piping system to the recirc line and a properly designed hydronic system with external heat exchanger. This approach is good for smaller radiant systems, while the Combi boiler is best for a whole house system, such as you are asking about, Vandal. Their technical support team is decent and almost always available within a minute's wait on the phone. They also work well as 2nd stage heaters backing up a solar radiant heating system, as shown below from one of our jobs using an Earthstar drainback solar tank and Earthstar Radiant Heating Control panel.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Spin it however

    You want but it is not a boiler. Does not have the ratings as a boiler and the warranty is 1/2 of a condensing boiler. You also have no means of outdoor compensentaion.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • HomeOwner1
    HomeOwner1 Member Posts: 134
    You are incorrect.

    It is a boiler. It also has an outdoor sensor option to compensate and modulate as you say.

    Please stop posting inaccurate information as this is very frustrating for homeowners trying to research their options and figure out the facts.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Dear Homeowner

    This is about the 3rd thread you have posted that we are providing incorrect information. Just so you know Navien in Sept of 2012 stopped offering the NON ASME version of the CH Series. So in all these old threads we are correct in stating that the CH Series is not rated as a boiler.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • HomeOwner1
    HomeOwner1 Member Posts: 134
    You are incorrect on warranty as well.

    Warranty is on par or better with just about every boiler we researched, 5/ 10 years. What are you taking about?
  • CMadatMe
    CMadatMe Member Posts: 3,086

    Is not better then a Viessmann Vitodens.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
This discussion has been closed.