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DIY: Radiant heating PEX spacing - Climate Milder Winter - West Coast

Marvin007 Member Posts: 52
edited May 2022 in Radiant Heating
Hi, I live on Vancouver Island, BC Canada. The temperature here where I live in the winter sometimes dips to -1C (30F) to -4C(25F) at most for maybe 1-2 weeks in the winter with most nights in the winter months around 4C(39F).

I currently have 2x 30,000 BTU gas insert fireplaces with blowers (1x upstairs/1x downstairs)

My bathrooms and kitchen on the main floor are tiled so they have cold surfaces. I am looking to install a radiant pex/aluminum fin system under the upstairs floor from the basement. My basement ceiling is completely open at the moment. I would also like to replace my water heater with a tankless on demand water heater. I have about 1400sqft upstairs floor that I want to heat using pex/aluminum fins as well as run 4 radiant baseboards downstairs off of the radiant system. My basement is 1500sqft and has a gas insert already.

My water is pretty soft, there is almost no buildup in my coffee maker after 12 months of use daily.

Questions I have about building my system:

1. Since I am going to replace my water heater with a gas tankless on demand. Should I buy 1 tankless water on demand and use it in an open loop system configuration ?

2. Since this is not my only heating source what size of pex should I run on the underside of the floor and how far apart should the pex be spaced in this geographical location/temperature climate?

3. When I buy a manifold do I need a zone for every room? This seems like a lot of zones for a house 10-12 zones and added cost for the actuators/temperature sensors facilitate these zone.

4. Is there a way to connect multiple rooms(loops) to one temperature controlled zone? If so what does one of these splitters look like when it is connected to the zone source and zone return on the manifold?

5. If I have and open concept area of my house such as a living room, hall, front foyer and kitchen would it not be wise to have all of these loops connected and monitored by 1 zone and thermostat?

Here are the size of my room runs that I have calculated...See picture.

Thanks for your suggestions.


  • Hot_water_fan
    Hot_water_fan Member Posts: 1,638
    edited May 2022
    What’s the motivation behind the tankless water heater? Space savings? I don’t particularly love any of the boiler/water heater options presented - tankless don’t do great with central heating (they’re designed for DHW) and 3 showers is a lot to handle. Combis can work, but same capacity concerns.  You can get the same or better efficiency with a tank, which is why I ask about space. 

    In a mild climate, heating only a handful of rooms, consider electric underfloor heating. Might be more expensive to run, but with a small footprint and that climate could be cheaper and easier to install. 
  • Ironman
    Ironman Member Posts: 7,225
    You would be wise to contact one the radiant designers on here like @Steve Minnich.

    There's much more to this than you may realize and proper design is the key. That starts with an accurate heat loss calculation.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Marvin007
    Marvin007 Member Posts: 52
    edited May 2022

    This is a Reno so I have to accommodate some existing issues (space, existing basement ceiling height 7.5 ft unfinished, 4" concrete basement floor with vapor barrier underneath)

    I am completely renovating my house which seems to be well built with douglas fir studs (70's) (new windows, new insulation (basement/ceiling/attic, but not outside walls), tile in kitchen, tile in bathrooms). I have already upgraded my houses entire plumbing to PEX from copper.

    I have already lived through 1 winter here using only 1 fireplace (30000 BTU) and 1x baseboard on the main floor. The currently uninsulated basement needed to be heated with 1x baseboard and a dehumidifier was used to get rid of the moisture, which was very expensive. I have also upgraded my natural gas line to accommodate multiple fire places and multiple gas systems(1 tankless, 2 tankless, or combi boiler)

    The point of a tankless water heater was simplicity: 1 unit, cheaper replacement costs (incase it breaks in 4 years), less piping, less exhaust vents, 1 unit to maintain, space savings (I am crammed for space).

    3 showers: I'm sure they won't all be on at the same time, but their could be the odd time. I did have the choice of electric in floor heating on the main floor for tiled rooms but the cost to run it was not appealing considering I have natural gas and I figured with the milder temperatures I might as well enjoy a warmer floor throughout the upstairs by adding a secondary heating system to facilitate this. I will not be heating the basement with in floor anything because there will be too much loss of ceiling height to insulate the concrete floor correctly or loss of heat through the concrete (4" concrete with a vapor barrier below). I am simply going to use 1" dricore subfloor panels and laminate flooring in the basement with radiant baseboards and a fireplace (30,000 BTU blower) in the rec room.

    It seems like a lot of work running the PEX between all joists but I will be doing it by myself (I would not be able to afford it if someone else was to install it) and the entire basement ceiling is open at the moment (it won't be an accessible later). I figure I can carve up the zones to run the PEX between the joist back to the manifold now so I can move on with the rest of the Reno. Later on I can install the correct tankless and plumb it to the manifold. I figure I can decide to heat tiled rooms first and if need be eliminate the laminated floored rooms if I run out of money or simply can't heat all floors with 1 tankless adequately. I do need to move forward with the rest of the Reno as I really need to finish it as soon as possible.

    #1 heat tiled floors with PEX in floor between joists
    #2 heat 2x bedrooms and 2x bathrooms with radiant baseboards in the basement
    #3 Heat the remainder of the laminated floors on the main floor with PEX in floor between joists
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,638
    The point of a tankless water heater was simplicity: 1 unit, cheaper replacement costs (incase it breaks in 4 years), less piping, less exhaust vents, 1 unit to maintain, space savings (I am crammed for space).

    The space savings are real, as are the piping and exhaust vents! I'm less convinced about the others, and that's assuming you use a combi, not a DHW tankless. You're really adding on a lot of work/expense with the hydronics here, Godspeed!