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Community and Q&A

Hydronics In Garage

kwoolfsm | Posted in General Questions on

Hi GBA Team,
   We’ve built a new home, we have the builder rough in hydronics in the basement and garage.  Since possession, I’ve had three hydronic installers come through to price out completion.  They qoutes were very high given what I saw as the simple requirements.  They were also drastically different in the system design aspects, which I’ve come to learn is common in hydronics, 13 ways to slice and dice each installation.  Soooo I’ve decided I want to try to tackle my own installation for my garage.  It’s a 2 loop (2 supply, 2 return) garage, 24×26 total length of 2 loops is 570 ft.  I have done some homeowner plumbing and am comfortable working with pex. I’m tempted to install a small 25 gallon electric (likely220v) water heater, with a basic (taco or grundfos or something else you may suggest)  circulation pump, and axiom glycol feeder tank.  I took a look at the various system proposals from the pro’s and noticed they all included expansion tanks as well. Am I wrong, do I need both, or does the axiom cover off the need for expansion tank, as it’s a pressurized feeder? I would buy a simple manifold from any one of the many pre-built manufacturers.  Simple thermostat control, for on/off on the circ pump, as I am not worried about overshooting the temp for short periods for comfort, as I will dial that in over the winter…It’s a garage, to melt snow and keep the cars above freezing.  Any other thoughts I should consider?   Thanks, and yes, I am a hack, but willing to give this one a try, no harm no foul.

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  1. Expert Member
    Akos | | #1

    Pressurized hot water is one of those things that can go bad very quickly, not necessarily the best to DIY. You generally can't use a water tank for space heating unless it is rated as such (I don't think any resistance ones are). A small resistance boiler that is rated for space heat costs the same anyways. You always need an expansion tank in a closed system.

    One issue with snow melt in garage in cold climate is where the water goes. The most common way is to slope towards the door, when the water hits the cold outdoor concrete and door seal, it tends to freeze there making the door hard to open.

  2. paul_wiedefeld | | #2

    I'd look at an electric boiler manual and install it just like that: so expansion tank, make-up water, valves, air vents, circulator, etc. Looks like you can get a 9kbtu/h electric boiler, that'd probably be great for this application.

  3. Expert Member
    DCcontrarian | | #3

    The reason hydronic installation is so expensive is there's a lot that can go wrong. This is not to dissuade you -- you have a huge advantage being on the premises, a guy who has to keep coming back over and over again is going to eat up all of his profit in those return trips pretty quickly. I'd be especially wary of installing a system where someone else installed the tubing, you have no idea what's down there and once you touch it you kind of own it.

    Most problematic hydronic installations were never engineered, if they had been engineered it would have been apparent from the beginning they weren't going to work. Basically you have to be able to put enough heat into the floor that you can get enough heat out of the floor to heat the space, without the floor getting so hot as to be uncomfortable. That is not always even possible, and when it's possible there is often a narrow band of designs that will work. But your tubing has already been laid so the die is cast -- or more accurately, the slab is cast. But we are a bunch of nerds here and we can help you through the calculations to make the most of what you have.

    A resistive heater is going to have the highest possible operating costs, I think you really should look at the long-term costs before going that way. An air-to-water heat pump will cost about a third as much to operate. The initial cost is more -- $5k or so -- but I think you'll find when you look at the cost of a heating rated electric boiler and all the fittings and accessories it's not outrageously more.

    I strongly recommend against the use of a glycol feeder or any kind of automated feeder. Hydronic systems are supposed to be closed, if they need regular makeup water it means they're leaking somewhere, and in the long run that leak is going to be damaging to your equipment and your house. I understand why pros like them. In a new installation, it can take days or weeks for all of the air to work its way out of the system. If the installer puts on an automatic air bleed and a makeup valve, he's done. He can shake hands and go cash the check and the air will escape on its own, he won't have the homeowner calling him every week to come back and bleed some more air. But this is where you have the home field advantage, you can chase down every air bubble and then seal the system and make sure it stays sealed.

    Things like circulators, thermostats and expansion tanks will all depend upon your choice of heating source, so get that settled first.

    1. Expert Member
      DCcontrarian | | #4

      I'll add that there is a belief that hydronic floor heat is more cost-effective, in that it creates more comfort for the same heat input. That hasn't been my experience.

    2. kwoolfsm | | #5

      I'd priced out the Air-Water heat pump as a whole home solution... $43000 CAD and that didn't include the hydronic connections to the existing rough-in... If you meant Heat Pump Water heater, those are close to $5000 locally...

      1. Expert Member
        DCcontrarian | | #6

        Heat Pump water heater won't work for space heating, it takes the heat from the interior.

        That sounds really high. DIY a heat pump shouldn't be any different from DIY a resistive heater -- you hook up the electricity, the water in and the water out. That's it.

    3. paul_wiedefeld | | #7

      For a garage this size operated at a low set point, I think cheap install outweighs cheap operating costs.

      1. Expert Member
        DCcontrarian | | #8

        If you're going with resistive heat there's no advantage to putting tubing into the floor instead of just electric resistance wiring. In fact there's lots of negatives to tubing.

        The question really is, if the tubing is there, what's the way to make the most of it?

        1. paul_wiedefeld | | #11

          Right but spending tens of thousands to save a little isn’t getting the most out of a small space like this.

  4. kwoolfsm | | #9

    Thanks for the replies, a couple of points to add to the conversation, and maybe help me clear up my own ambiguities:
    - related to the concern of a pressurized hot water system: our mainline inlet pressure from the city is 75psi (typically), pex has higher capactiy than that, whether the tank is connected to DHW, or closed loop glycol heating loop, it is pressurized no? Each of the professionals quoted this axion pressurized feeder. Can you expand on this as a flaw, or merely a caution towards the DIY guy?
    - locally there are lots of homes using the hot water tank as hydronic heaters, while not widely accepted in the newer home building codes, they are grandfathered as long as the DHW and heat loops are seperated from cross-contamination. With retrofits I see and have spoken to plumbers that often install a second tank dedicated to the heating loop.
    - Of interest, if the pressure is a significant objection of risk (I work in Health and Safety so kinda looks bad on me....hahah), I don't mind using the air vents, they just hadn't been part of ANY of the professional designs I'd seen on this home.
    - The loops were designed and engineered by a licensed hydronic team, the reason we stopped at rough in, they quoted $42000 CAD for boiler and connections, this is beyond the $19000 for roughing in the pex in the slab
    - I'm happy to look at the smaller boilers, was thinking they are more complex than using the smaller tanks? One contractor suggested using a plate exchanger off my main DHW tank as a option, the cost reduction was not much in his quote, so didn't seem like a smart move, to scavenge from my dhw supply (we're a family of 5)...
    - I'm not worried about the melt and runoff, whether the garage is heated with a gas heater, electric or hydronic, melt and runoff is a pain, the hydronic may actually be a better evaporator...
    Again, thanks for sharing your expertise and knowledge.

    1. paul_wiedefeld | | #10

      Keep the loop closed, entirely separate from your drinking water. The system will be pressurized, just not at 75psi - probably around 10. The electric boiler wouldn’t be any more complicated and isn’t that expensive. I think following a manufacturer’s guidance here is the easiest, safest path.

    2. Expert Member
      Akos | | #12

      This is about what you need. You can either buy or make it:

      Instead of messing with any autofeed and such, I think the simplest is to install something like a drainback tank in flow through above the pump assembly. This way you can simply fill the tank and any air in the system collects there.

    3. Expert Member
      DCcontrarian | | #13

      Hydronic systems typically run at pressure around 10-14 PSI, if you only have a single floor you'd be at the lower end of that. The expansion tank is there because the hydronic system is closed. Water expands when heated and is essentially incompressible, it can create enormous pressures when it is heated in a sealed container. The pressure can burst pipes, and can even cause a dangerous explosion.

      You're going to need, at a minimum:
      1. A source of hot water
      2. A circulator pump
      3. A thermostat
      4. Some sort of control circuitry to control the circulator from the thermostat.
      5. An expansion tank

      I know some people circulate their domestic hot water in radiant loops, but it's a bad idea. That's your drinking water, that's a good way to contaminate it with bacteria and make your family sick.

      To use your hot water heater indirectly, you need some sort of heat exchanger. There's basically two types. With an indirect tank you have a tank of water with a coil in it, hot water runs through the coil and warms the water in the tank. An example is the Chiltrix DHW80, which runs about $2300. With a flat plate you don't need a tank, but you need some way of balancing the heat in with the heat out. Taco makes one that is a heat exchanger with the control logic -- -- it's about $1500. In either case you also need another circulator to circulate water from the domestic tank.

      The other option is a dedicated heat source, which would either be an electric boiler, a heat pump, or something you cobble together. In terms of cobbling, one option would be to buy a water heater and just use it until it breaks and then replace it. At my Home Depot electric water heaters start at around $400. Another option would be an inline heater. Chiltrix sells a 5500 W/ 18,000 BTU inline heater ( ) for $399. It's not ideal because it's meant to be used as a backup heater on their heat pump systems, so you'd have to improvise control circuitry for it. It looks to be just a repurposed spa heater so you might want to look at spa heaters.

      Nothing that you cobble would meet code. And you need to know what you're doing to mess around with electricity and plumbing, especially heating fixtures.

  5. jberks | | #14

    First of all, I'm amazed at what costs get transacted for radiant rough-ins. I can understand your drive to tackle this yourself. Radiant isn't overly done here in Canada, so there isn't much common knowledge to rely on when you're doing it yourself. So I'll just say heed the advice the others have brought here.

    To Malcolm's point, what does your drainage look like? you didn't answer that. Most garage slabs are sloped towards the door. It would suck if you spent tons of time and money building this system, to have your garage door frozen shut on you every winter. Or is this handled by having radiant laid beyond the door to keep the gasket warm? I say this becasue I've once built a snow melt system that didn't drain well enough and it just creates hockey rinks after it melts the snow to water and the water freezes again. although you won't bring that much snow into the garage, it is definitely something to consider deeply.

    Also consider an HRV to get air circulation, ventilation and to remove humidity.

    To a question on your original post, the axiom glycol feeder does not act as an expansion tank. The glycol feeder tank holds extra glycol/water to feed into the system, usually for big systems, and as mentioned, provides a certain automation during the first month while the air is being eliminated through the system. Your garage system is tiny, you might not even notice a pressure drop after the air is eliminated. So I'd say don't bother with it for your purposes. Keep on eye on the pressure yourself. The expansion tank houses air pressure behind a bladder. it act as a pressure buffer in the system so when the water heats up and increases system pressure, the entire system can handle it without possibly rupturing. You absolutely need an expansion tank and a T&P valve within the closed loop side for safety.

    If you have a gas tank DHW heater nearby, you might as well run a loop to a plate heat exchanger off that, creating a DHW side and a Closed loop Radiant side. In my opinion, its extremely inefficient to getting a new gas boiler for 600sqft, and if you're going to use electric, you might as well just buy a $100 electric space heater and call it day.

    If you're still hellbent on doing radiant, You'll need a circulation pump on the DWH side (Bronze or Stainless steel for Potable use, you can't use cast Iron) to the exchanger and I suggest piping a thermostatic valve so you can control the water temp. Running it at lower temps will allow you to run the system longer to not overheat the garage and not retain much in the slab. Other things you'll need on the closed side is another circulator, pressure gauge, air and dirt eliminator, balancing manifold, glycol, a control board and a thermostat or some other initiation device, etc.

    Check out some of caleffi's resources. Their Youtube channel provides many hours of engineering, systems design and install experiences.


    1. Expert Member
      DCcontrarian | | #16

      "If you're going to use electric, you might as well just buy a $100 electric space heater and call it day."

      This really is Option Zero, the one which all other options should be compared to. A 1500 Watt heater puts out 5000 BTU/hr.

      The only reason to consider something else is greater operating efficiency (gas, heat pump) or greater comfort.

      1. MartinHolladay | | #17

        Another thumbs up for the $100 electric space heater (or a length of electric resistance baseboard). Same energy cost.

        1. Expert Member
          DCcontrarian | | #18

          Actually, Amazon has 1500W heaters for about $25.

      2. paul_wiedefeld | | #19

        Plus unlike a slab, the baseboard will put out heat quickly. Otherwise, you have to heat thousands of pounds of rock before any heat warms the garage.

        1. Expert Member
          DCcontrarian | | #20

          And unlike a slab, a baseboard shuts off when the thermostat turns off.

          A quartz infrared heater might be a good choice for a space that's only heated intermittently.

  6. Mountain_Man_CO | | #15

    If you are running hydronic heat in the garage, are you also running it in the basement? If so, why not heat the whole house with it? Hydronic panels or radiators can heat the whole house with tubes in the floors, ceilings, and/or walls. Likewise, you can have small radiators controlled by a simple valve/thermostat called a TRV.

    If you add fan coil units with drip pans, you can install them on exterior walls and feed them chilled water from an air-to-water heat pump and also cool spaces that way. I prefer a heat pump these days to a boiler (either a conventional or mod-con one) because you can often add solar to make electricity and even hot water and end up with a net-zero home.

    Hydronics are fairly DIY friendly, which is good, because most installers will charge a lot for these "higher-end" systems that aren't tried-and-true ductwork and convective heat & A/C they install of the time. And you can make them as simple or complex with zoning and piping as you prefer.

    These days with tighter and better-insulated homes, one should add ductwork for ventilation via an HRV or ERV, plus cooking exhaust with make-up air if going down the hydronics path.

  7. kwoolfsm | | #21

    Hi GBA Team,
    Here's small update. In April of 2023 we installed a ducted heat pump/furnace system. At the same time I installed an Emporia Energy Monitor, along with a bunch of circuit monitors. At the end of 2023, this garage heater, a 4000W/220V Stelpro Spider ceiling heater. For the balance of the year, that heater made up ~42% of my electrical usage during heating months. I am heading towards a solar install in a couple months, so my give-a-Sh@t factor will decline rapidly, as the system design is 116% of my annual usage. The comments above about operating costs vs install costs are not lost. Total install indlucing wire, electronic thermostat, and heater was <$1000. As much I love the idea of hydronic and some new fancy mechanicals, it would end up being my 3 heating system in the house. Heat Pump, Nat gas furnace and TBD hydronic heat source. Complexity be damned.... The elctric heater provides more than enough heat to keep the garage warm enough to melt snow off the minivan, and keep garage products from freezing. It's not fancy, but it's good enough. Thanks to those that provided details, considerations, factors and experience. BTW - I love the central ducted heat pump system, but found some programming issues along the way, and my installer has been great. So worry more about "after-sales" support, The Daikin may or may not be a fan favorite, but my installer support has been fantastic.

    1. Expert Member
      MALCOLM TAYLOR | | #22


      Thanks for coming back to provide an update. Often we never hear how things turn out and don't get the benefit of the lessons learned.

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