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Will the Takagi T-H3M-DV-N run radiant heat and hotwater

zmann96
zmann96 Member Posts: 24
I have a two family home in New Hampshire. I installed a system for my son but he used a boiler. I've been on some forums and they say yes it works and then a plumbing supplier says it won't and will put too much on the heater. My side is 1100 sq ft and I'll have 2100 feet of 3/8" pex. the house is insulated. I'm looking to use the Takagi T-H3M-DV-N for both the radiant and domestic hot water. Any advice.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 18,951
    Don't. The Takagi T-H3M-DV-N is a very good tankless water heater. It is not, and is not meant to be, a heating boiler. Will it work? Yessss…. but it's the wrong tool for the job.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    SuperTechzmann96kcopp
  • zmann96
    zmann96 Member Posts: 24
    Thanks Jamie. I'm trying to find a tankless that will work. My son's that I did is on a gas boiler tankless but the boiler runs to maintain 160 degs. and it's not needed all the time especially spring and fall. any suggestions.
  • hot_rod
    hot_rod Member Posts: 16,315
    And, you really don't want to combine the heating and plumbing water, called an open or combined system

    Combi boilers can be a good compromise. if you want an all in one product.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zmann96kcopp
  • zmann96
    zmann96 Member Posts: 24
    I was going to use a heat exchanger to separate the heating from domestic.Not a good idea?
  • zmann96
    zmann96 Member Posts: 24
    question, if I were to just use an instant hot for the radiant without using it for domestic hot water will it work?
  • Zman
    Zman Member Posts: 7,330
    There are a lot of good options between an always hot tankless coil and using a water heater as a boiler. I would suggest a mod/con boiler with indirect tank.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    zmann96GroundUp
  • SuperTech
    SuperTech Member Posts: 1,792
    > @zmann96 said:
    > question, if I were to just use an instant hot for the radiant without using it for domestic hot water will it work?

    @Jamie Hall said it best. It will function but not as well as and for as long as a properly installed and sized boiler.
    zmann96
  • hot_rod
    hot_rod Member Posts: 16,315
    A tankless water heater is designed to heat small quantities of water 3- 5 gpm over a wide temperature difference say 40- 120F

    Boilers are designed with a completely different task, high flow rates, low temperature differential.

    As such the internal design, control, etc is quite different.

    With so many great choices for the right product why try and force a tankless to do something it is not designed, or comfortable doing?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zmann96
  • zmann96
    zmann96 Member Posts: 24
    Thanks Hot Rod. I understand. Well I do Have a 50 gal Natural Gas 50 gal. State Water heater GS6-50-YBVIS 200 45 GPH. It's power vented and is somewhat efficient only a year old. Do you think I could with a heat exchanger do both DHW and the radiant?
  • hot_rod
    hot_rod Member Posts: 16,315
    zmann96 said:

    Thanks Hot Rod. I understand. Well I do Have a 50 gal Natural Gas 50 gal. State Water heater GS6-50-YBVIS 200 45 GPH. It's power vented and is somewhat efficient only a year old. Do you think I could with a heat exchanger do both DHW and the radiant?

    Yes I like that much better. There used to be several companies that build a complete box to do that had pump, HX control, piping inside.

    What is the BTU of that heater? A high output 65- 75,000 BTU would be ideal.
    I suspect on design day you may need 25,000BTU/ hr. for the home.

    Any backup options? On the coldest days you don't have a lot of BTU to spare.

    Simple enough to build your own

    HX, a couple circulators, air purge, exp tank some purge valves
    relay box, thermostat

    Here is a drawing I modified a bit to show the concept.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GroundUp
  • kcopp
    kcopp Member Posts: 3,990
    Where in NH are you? Im on the Seacoast... perhaps I can assist. kevin
  • zmann96
    zmann96 Member Posts: 24
    hot_rod said:

    zmann96 said:

    Thanks Hot Rod. I understand. Well I do Have a 50 gal Natural Gas 50 gal. State Water heater GS6-50-YBVIS 200 45 GPH. It's power vented and is somewhat efficient only a year old. Do you think I could with a heat exchanger do both DHW and the radiant?

    Yes I like that much better. There used to be several companies that build a complete box to do that had pump, HX control, piping inside.

    What is the BTU of that heater? A high output 65- 75,000 BTU would be ideal.
    I suspect on design day you may need 25,000BTU/ hr. for the home.

    Any backup options? On the coldest days you don't have a lot of BTU to spare.

    Simple enough to build your own

    HX, a couple circulators, air purge, exp tank some purge valves
    relay box, thermostat

    Here is a drawing I modified a bit to show the concept.

    Hot Rod, the hot water heater only produces 40K BTUs
  • zmann96
    zmann96 Member Posts: 24
    kcopp said:

    Where in NH are you? Im on the Seacoast... perhaps I can assist. kevin

    Kcopp I'm in Laconia.
  • hot_rod
    hot_rod Member Posts: 16,315
    zmann96 said:

    hot_rod said:

    zmann96 said:

    Thanks Hot Rod. I understand. Well I do Have a 50 gal Natural Gas 50 gal. State Water heater GS6-50-YBVIS 200 45 GPH. It's power vented and is somewhat efficient only a year old. Do you think I could with a heat exchanger do both DHW and the radiant?

    Yes I like that much better. There used to be several companies that build a complete box to do that had pump, HX control, piping inside.

    What is the BTU of that heater? A high output 65- 75,000 BTU would be ideal.
    I suspect on design day you may need 25,000BTU/ hr. for the home.

    Any backup options? On the coldest days you don't have a lot of BTU to spare.

    Simple enough to build your own

    HX, a couple circulators, air purge, exp tank some purge valves
    relay box, thermostat

    Here is a drawing I modified a bit to show the concept.

    Hot Rod, the hot water heater only produces 40K BTUs

    Input BTU rating?

    If so, X 78% efficiency= 31,000 actual output. sorry!

    Room to add another gas HW tank? That is the least expensive option for those low load jobs.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zmann96
  • zmann96
    zmann96 Member Posts: 24
    hot_rod said:

    zmann96 said:

    hot_rod said:

    zmann96 said:

    Thanks Hot Rod. I understand. Well I do Have a 50 gal Natural Gas 50 gal. State Water heater GS6-50-YBVIS 200 45 GPH. It's power vented and is somewhat efficient only a year old. Do you think I could with a heat exchanger do both DHW and the radiant?

    Yes I like that much better. There used to be several companies that build a complete box to do that had pump, HX control, piping inside.

    What is the BTU of that heater? A high output 65- 75,000 BTU would be ideal.
    I suspect on design day you may need 25,000BTU/ hr. for the home.

    Any backup options? On the coldest days you don't have a lot of BTU to spare.

    Simple enough to build your own

    HX, a couple circulators, air purge, exp tank some purge valves
    relay box, thermostat

    Here is a drawing I modified a bit to show the concept.

    Hot Rod, the hot water heater only produces 40K BTUs

    Input BTU rating?

    If so, X 78% efficiency= 31,000 actual output. sorry!

    Room to add another gas HW tank? That is the least expensive option for those low load jobs.
    Yes, I have plenty of room for another tank. do you hook the two tanks together at the heat exchanger for the loop for the radiant heat. Thanks again
  • hot_rod
    hot_rod Member Posts: 16,315
    One tank dedicated to DHW, the other just for the radiant.

    Tank type water heaters can be a nice heat source as their volume makes for a nice buffer.

    Since most do not have an ASME certification no all contractors can or will install them. Check with local code officials.

    At 12- 15 psi operating condition they are plenty safe in my mind. Leave all the safeties in place, like the T&P valve, add an additional 30 psi relief if you want low pressure protection.

    I would also run it 120- 130° and use a mix valve if you need lower temperature to help prevent extended condensation in the tanks. Tanks set at 100F do not tend to last long without problems,

    I have used both gas and electric water heaters from 2-1/2 gallon up to 50 gallon for radiant heat sources.

    Bradford White builds a CombCor 2 which is a high output tank water heater with a coil inside for radiant. So an approved dual use tank. I believe they are special order only, now. They were commonly found on some wholesalers shelves, years back.



    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    zmann96
  • zmann96
    zmann96 Member Posts: 24
    hot_rod said:

    One tank dedicated to DHW, the other just for the radiant.

    Tank type water heaters can be a nice heat source as their volume makes for a nice buffer.

    Since most do not have an ASME certification no all contractors can or will install them. Check with local code officials.

    At 12- 15 psi operating condition they are plenty safe in my mind. Leave all the safeties in place, like the T&P valve, add an additional 30 psi relief if you want low pressure protection.

    I would also run it 120- 130° and use a mix valve if you need lower temperature to help prevent extended condensation in the tanks. Tanks set at 100F do not tend to last long without problems,

    I have used both gas and electric water heaters from 2-1/2 gallon up to 50 gallon for radiant heat sources.

    Bradford White builds a CombCor 2 which is a high output tank water heater with a coil inside for radiant. So an approved dual use tank. I believe they are special order only, now. They were commonly found on some wholesalers shelves, years back.



    I was looking at the Combi boilers. Lowes has a Rinnai M120CN 95% and 4.2 gpm. DHW. it's selling for $2658. I can get a 20% employee discount from a family member. Liberty Utilities will give me a $1500 rebate and Uncle Sam will give a $150 tax credit costing me in the end $476.00 I don't want to base the heating system on my savings along. I want it to be efficient and do the job as well. The boiler has a 12 warranty 2 years parts. your thoughts?
  • hot_rod
    hot_rod Member Posts: 16,315
    I have not installed that brand personally. What I have found is most every brand and model of boiler you can find rave reviews and terrible reviews.

    I stick with brands that support me from the dealer, rep, and manufacturer.

    Look for the control features. I thing ramp delay or derate function is important, I like being able to add sensors, outdoor reset sensor should be included.
    Read the I&O manual for setup before you buy, are you able to understand the programming, some are super simple, others I've found super complicated.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • zmann96
    zmann96 Member Posts: 24
    well, as I looked into the rebates , it requires a license to apply for rebate. I've installed boilers and hot waters and radiant heat but don't have my license. Even if I paid to have a licensed plumber check my work and sign for me what I pay him would defeat the rebate. I think your advice of a hot water heater makes the most sense for me. I was looking at the westinghouse hybrid . do you know what the flow rate is for it. It only has 130gpm for the first hr. nothing for continuous. There are so many options it's confusing. You are so right about reviews...crazy. I was thinking of the 50k - 100k unit ? for DHW and radiant.