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Retrofitting Hydronic Radiant Heating

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Hello Everyone,

I recently purchased a home and want to retrofit hydronic radiant floor heating throughout.

I was hoping I can get a couple of pointers from anyone who might have went through this already.

It's a 3 level home including the below grade basement. Basement is unfinished. 2300sqft excluding the basement.
I am planning to do the retrofit in multiple stages:
1) Living + Dining room (within next 3 months)
2) Kitchen + Foyer + Powder room (next year)
3) 2nd floor bedrooms/bathrooms (2021)
4) Basement (TBD)

I am unable to install the PEX between the joists because the builder did a sloppy job and drove nails through the subfloor when framing so they are protruding through the joist bays. The only option is to do a sandwich install.

The WarmBoard type products are quite expensive so I was thinking I'd lay down 3/4" plywood on the subfloor and make 5/8" deep channels with a round 5/8" router bit for the 1/2" PEX tubing. I can then install aluminum heat transfer plates unto the channels. Any thoughts on this approach?
What do you do about the doors and door frames once the floor gets elevated by 3/4"? Do I need to cut the doors?

I was also thinking of doing a zone per level and perhaps planning for future heating garage/driveway. My levels, however, have a mix of eng. hardwood and tile flooring. Do I install sensors in the hardwood since it can be damaged by high heat? Should I make separate zones for each floor type?

There is only one thermostat in the house right now on the main floor. Are there any wireless options for the other thermostats? I guess I could tap into the phone-line wiring since I have no use for it otherwise.
Does the thermostat and the relay have to be the same brand/system? I'm in general confused about the relationship between thermostat <-> relay <-> pump, would appreciate some light on it.

I was considering a heat exchanger but was reading about some people having issues with them managing to heat the entire house. I want a closed system. Is a separate on demand gas heater the best option?

I apologize for the general questions, but am struggling finding cohesive information online on how to approach this.

Thanks for your help!

Comments

  • gaabbee
    gaabbee Member Posts: 43
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    I retro fitted my whole house last year so I can try my best to help you out. This will be a lot of work, physically and mentally. First off you will want to do a room by room heat loss calculation. Slant fin has a great app for this. Knowing the heat loss lets you design the system you need.

    For my system the heat loss was around 25k btu total. You want to shoot for a delta T of around 10 degrees and you don't want your surface temps to be above 84*. Do not run 1/2 inch pex longer then 300 feet per loop.

    I did 6' strips of 3/4' plywood and ran the pex in between with aluminum transfer plates. Then put floating floors above. You will have to cut some doors. I would run the same temperature water throughout using a variable speed pump and a smart mixing valve to regulate the water temp based on outdoor reset.
    Using zone valves on loops to different floor types.

    The zone valves can be controlled by a taco zone valve controller. Each zone can have a thermostat (any brand) wired to the controller. A taco switching relay could be used in place of the ZVC if you decide to use pumps in place of zone valves. Then each thermostat would control the pump for that zone.

    I also use a heat exchanger to separate the radiant side (gylcol) and boiler side (water). I use a 100k btu heat exchanger but may up size it in the future. Go over sized on these. I also have a reverse indirect tank on the boiler side. This prevents short cycling and also provides my domestic hot water.

    People say not to use on demand type water heaters for these applications and use an actual space heating type boiler. After all my research and work its been so worth it. Take your time and read as much as you can on here, greenbuilders, and caleffi.
    vitalious
  • HomerJSmith
    HomerJSmith Member Posts: 2,483
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    A cheap 4 1/2" grinder from Harbor Freight will take care of the nail protruding thru the floor. If you decide to do underfloor be sure and use heat transfer plated and insulate against backloss.
    ZmanCanuckervitalioushagani
  • Zman
    Zman Member Posts: 7,589
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    Installing from underneath is the simplest option, even if you have to cut the nails. As Homer said, a cheap grinder with an offset cutting wheel will make quick work of it.

    The only reason people use tankless water heaters for heat is that they are cheap. It is not the right product and will fail prematurely.

    On the t-stats, with the amount of work you are doing, just fish new 4 conductor t-stat wire and be done with it. Phone wire is too light gauge and wireless a PITA. Keep in mind that a t-stat is just a 2 wire switch. Some smart or WIFI models need a common to support other functions.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    vitalious
  • vitalious
    vitalious Member Posts: 4
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    Gaabbee, Homer, Zman,

    Thank you all for the reply!

    My notifications were off by default so sorry for the delayed reply.

    Gaabbee:
    Pardon my ignorance, but the delta T refers to the difference between the water going into the zone and back from it?

    For the doors, did you have to do any work on the door framing itself? What about the toilets?

    It didn't occur to me to cut the nails with a grinder - that would work well. But I forgot to mention in my initial post that the hardwood flooring in the house is done very poorly and the tiling is old so I wanted to replace it first thing. That is why I thought about doing the sandwich install. Does it still make sense to do staple up if I'm ripping out the floors anyway? I feel that heating the floors through the subfloor would be far less efficient. Is that correct?

    Also, looking at what's involved with a staple up install (drilling the joists, threading the pex through the bays, stapling up the fins, adding reflective material, adding insulation), it sounds just as difficult as doing a sandwich install, if not more. Am I missing something?.

    I definitely want to go with the simpler solution if its appropriate for my scenario.

    Thanks for shedding light on the heater.
    My home came with a boiler rental ($22.60 / month). I like the heat exchanger option. Do I need a pump to circulate the hot water through the HE or is it enough to only move the cold glycol?
  • vitalious
    vitalious Member Posts: 4
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    I decided to buy Modern Hydronic Heating instead of loading you with stupid questions.

    I would, however, still like to discuss the topic of staple-up vs sandwich install.
  • Dave H_2
    Dave H_2 Member Posts: 558
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    Do it from below! You've got the space, it sounds like you have the time and whether you heat from above with a sandwich method or below with plates, it almost doesn't matter. You still have to heat the entire floor assembly before any heat rises into the room.

    My motto is " make the radiant fit the house, don't make the house fit the radiant"

    You can mix and match based upon what you run into when you start exposing all of the bones in your home, whats the easiest, and what ends up being least expensive. The end result is radiant floor heat done right.

    I have a mixture of all four in my home, under floor with plates, underfloor without plates, sandwich and slab.

    When you buy the sandwich method, you end up spending money on the wood so you can have a level floor.....not for the radiant's purpose.
    When you go below, you don't need the extra wood material, screw the plates to the subfloor, insulate tight, then go.

    Dave H.
    Dave H
    vitaliousZman
  • gaabbee
    gaabbee Member Posts: 43
    edited October 2019
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    Yes that is the correct definition of delta T. Like Dave, I did sandwich and staple up in my house. Both have pro's and con's. Like your thought process I redid some floors in my house and those are the rooms I did the sandwich method. I've noticed better response time and warmer floors in those rooms.

    I say if you have access to below staple up is the easiest way to go. If the room is over say a crawl space and you plan to redo those floors go sandwich.

    If you have your kitchen as staple up make sure that loop/loops are controlled by thermostat in that room. If your bedroom is sandwich make sure that loop has it's own thermostat. You don't want a loop or room changing from sandwich to staple up because you will have different heat outputs. (hope that makes sense)

    I just cut the bottom of the doors about 3/4". Toilets you will probably have to raise up with a bigger pipe connection. They sell them at home depot or Lowes. I found the sandwich method easier then staple up but everyone is different. I for one did not want to lay on my back in a crawl space trying to run pex through joists. By the way pex is a major pain to work with when it is coiled up. Don't be like me and buy the 1000' roil to save a couple bucks or invest in a de-coiler.

    You will need 2 circulators with the HE. Look at primary/secondary piping models.
    vitalious
  • vitalious
    vitalious Member Posts: 4
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    gaabbee said:

    Yes that is the correct definition of delta T. Like Dave, I did sandwich and staple up in my house. Both have pro's and con's. Like your thought process I redid some floors in my house and those are the rooms I did the sandwich method. I've noticed better response time and warmer floors in those rooms.

    I say if you have access to below staple up is the easiest way to go. If the room is over say a crawl space and you plan to redo those floors go sandwich.

    If you have your kitchen as staple up make sure that loop/loops are controlled by thermostat in that room. If your bedroom is sandwich make sure that loop has it's own thermostat. You don't want a loop or room changing from sandwich to staple up because you will have different heat outputs. (hope that makes sense)

    I just cut the bottom of the doors about 3/4". Toilets you will probably have to raise up with a bigger pipe connection. They sell them at home depot or Lowes. I found the sandwich method easier then staple up but everyone is different. I for one did not want to lay on my back in a crawl space trying to run pex through joists. By the way pex is a major pain to work with when it is coiled up. Don't be like me and buy the 1000' roil to save a couple bucks or invest in a de-coiler.

    You will need 2 circulators with the HE. Look at primary/secondary piping models.

    gaabbee said:

    Yes that is the correct definition of delta T. Like Dave, I did sandwich and staple up in my house. Both have pro's and con's. Like your thought process I redid some floors in my house and those are the rooms I did the sandwich method. I've noticed better response time and warmer floors in those rooms.

    I say if you have access to below staple up is the easiest way to go. If the room is over say a crawl space and you plan to redo those floors go sandwich.

    If you have your kitchen as staple up make sure that loop/loops are controlled by thermostat in that room. If your bedroom is sandwich make sure that loop has it's own thermostat. You don't want a loop or room changing from sandwich to staple up because you will have different heat outputs. (hope that makes sense)

    I just cut the bottom of the doors about 3/4". Toilets you will probably have to raise up with a bigger pipe connection. They sell them at home depot or Lowes. I found the sandwich method easier then staple up but everyone is different. I for one did not want to lay on my back in a crawl space trying to run pex through joists. By the way pex is a major pain to work with when it is coiled up. Don't be like me and buy the 1000' roil to save a couple bucks or invest in a de-coiler.

    You will need 2 circulators with the HE. Look at primary/secondary piping models.

    Thanks for the reply.
    May I ask you what the spacing of your joists is?
    Mine are 12" OC and I'm struggling finding a double grooved heat plate that would work with that. Staple up does sound a lot easier than disturbing the living space for my wife and kid, I'm just concerned about it's efficiency vs a sandwich.
    Did you add reflective material and insulation?

    I've done some back of the napkin math and adding batts to the joists bays comes out to be more expensive than putting down plywood on top of the subfloor, so I don't see how staple-up is cheaper than sandwich. Though the real question is whether I'll be adding insulation to the bays anyway when finishing up the basement.

  • Zman
    Zman Member Posts: 7,589
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    I would install from underneath but there is nothing wrong with installing from above. Both systems will work well.
    This system would be the one for 12" centers https://www.rehau.com/us-en/mechanical-and-plumbing/radiant-heating-and-cooling/hydronic-radiant-heating/below-floor-plates#tab2
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kenjohnson
    kenjohnson Member Posts: 87
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    I just completed a below-floor install last year. It's working great. My post with details is here: https://forum.heatinghelp.com/discussion/163346/would-like-some-feedback-on-my-radiant-design-plans#latest

    You will need at least 3 people to run the radiant loops through joists under floors. If you bought Siggy's book, you must have the capabilities to design it yourself. It's not hard, just takes some math. Then the install just takes time.
  • gaabbee
    gaabbee Member Posts: 43
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    vitalious said:

    gaabbee said:

    Y
    Thanks for the reply.
    May I ask you what the spacing of your joists is?
    Mine are 12" OC and I'm struggling finding a double grooved heat plate that would work with that. Staple up does sound a lot easier than disturbing the living space for my wife and kid, I'm just concerned about it's efficiency vs a sandwich.
    Did you add reflective material and insulation?

    I've done some back of the napkin math and adding batts to the joists bays comes out to be more expensive than putting down plywood on top of the subfloor, so I don't see how staple-up is cheaper than sandwich. Though the real question is whether I'll be adding insulation to the bays anyway when finishing up the basement.

    Mine are also 12" OC but I used 2 separate 4 or 5 inch wide transfer plates. Don't worry about which is more efficient unless it's a high heat loss room, then go sandwich. You can also always air seal/insulate more if needed. Do what is easier. Take it room by room and decide which way to go. I have joist insulation in the rooms with crawl spaces and only some insulation in the joists with basement access. (I want to keep the basement some what warmer).
  • HomerJSmith
    HomerJSmith Member Posts: 2,483
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    Staple up--Always use heat transfer plates. Insulate against backloss. Leave 2" of room between the insulation and sub floor. If you have the joist space, fibreglass insulation will work. I use and have used rigid 1 1/2" foil Urethane insulation, messy but it worked good allowing the heat to spread evenly across the joist space.

    What you put on the top of the sub flr has a lot to do with the heat energy moving into the room. The lower the R value the better. Some pads and carpets have a high R value and require high fluid temperatures.