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Community and Q&A

Intermittently Heating Garage

_Stephen_ | Posted in Mechanicals on

Hi Guys,

I’ve got a problem I’m noodling around, and I’m hoping someone can offer some thoughts.

I’ve taken up indoor cycling in my garage.  Whilst doing this, I need the garage to be around about 14C – 16C, and I cycle roughly 5 days a week, for a cumulative time of about 6-8 hours.  So,  most of the time, I don’t care about the temps,  but for these specific times I do.

I am in southern Ontario, which I believe is Zone 4?  Garage has R20 batts, and is relatively well sealed as far as garages go.  Left completely to it’s own devices,  it holds about 7 degrees when it’s -5C outside.  Local 99% temps are around -18C.

I’ve looked at three options,  by order of install cost:

1)  Run an electrical subpanel to the garage,  at least 50 amps,  and setup a 7.5 kW electric heater.  I’d guess this would be around $1k.  House has extra capacity to do this (200 AMP panel, and we run natural gas water heater and stove, so lots of extra oomph there).  It’s simple.  It’ll always work.  It’s inexpensive to setup.  It’s pricey to run though.  I’m having a hard time figuring out how to estimate the energy usage of this kind of impulse driven heating style,  where it’s only warmed a few times a day.

2)  Get some sort of vented Natural gas heater, like the Mr. Heater Big Maxx or equivalent.  This has the advantage that I can hook up a smart thermostat and tell Google to switch on the heater when I start getting ready.  The 50k BTU device would certainly get the temp up in a hurry.  Estimated cost around $2k.  This has the disadvantage of needing to constantly cycle the heater from quite cold to quite warm regularly.  I’d be worried about condensation and ruining the burner tubes.

3)  Install a minisplit.  Most expensive option to install,  around $4k.  I’d probably need an 18K BTU device to bring the temps up in a reasonable timeframe.  Has the benefit of lowest CO2, and also provides AC in the summer.  This is really hard to justify though, because of the upfront cost.

Thoughts?  Is there a better solution I haven’t thought of?  Anyone have any idea how much it would cost to bring the garage from 5-6C to 14C using a resistance heater?


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  1. charlie_sullivan | | #1

    It's expensive to heat up the whole garage. It's a large volume, and the floor has a lot of thermal mass; in my case the tools and junk stored there add even more thermal mass. That also makes it hard to calculate how much electricity it will use, or what size heater you need to warm it up reasonably fast.

    A solution is to use radiant heaters. Something like this:

    You could use tripods as shown or mount them in the ceiling. One would probably do the trick but you could use several, maybe lower power, surrounding you. They directly heat your body (and your bike) rather than heating the air, and so you get instant response when you turn them on. And also, as you warm up and start to sweat, you can turn them down or off and instantly have the effective temperature you feel reduced.

    If you use more than one, just make sure you have separate circuits to plug them into.

    This type of heating is often used for something like a worksatation in a warehouse--it's less expensive to keep one spot comfortable with them than keep the whole space warm, even for continuous operation. The advantage is even greater if you are using the space intermittently.

    Get ones that have a reflector like that, not the ones that are a box with a fan--if it has a fan, that means it is delivering most of the heat by convection and the infrared feature is mostly decorative.

    Here's a cheaper, lower power one, in case you want to put an array of them on all sides of where you work out.

    Your other option, of course, is to start wearing many layers in the cold space and peel them off as you warm up.

  2. PLIERS | | #2

    If all you need is room to cycle wouldn’t be easier just to keep in a conditioned part of home. Usually they have wheels you can just move it around if need be. Maybe a bedroom? It’s going to be hard or expensive to set up a conditioned space for a very small price of equipment.

    1. _Stephen_ | | #4

      Hi Hammer,

      So what I'm doing involves my actual real bike hooked up to a smart trainer. So, it's got chain oil and requires maintenance. These things are a lot more tolerable in a garage where I don't particularly care if I get oil on the floor. It comes off the concrete very nicely!

      I also do want an environment that is somewhat colder than I would want to keep my house, or you overheat pretty quickly. I can put out north of 600-700 watts of heat myself sustained for over an hour, so you end up sweating a fair bit even in the relative cold, and even with a big pair of fans pointed at you.

      The sweating is another reason to keep it in the garage...

      I did have it setup in the basement, but found it intolerable for the reasons listed above.

      1. charlie_sullivan | | #7

        Your plan is to have a heater to keep you from getting too cold and two big fans to keep you from getting too hot? If I'm understanding that right, none-of-the-above would be a cheaper, quieter, and more efficient option. If the problem with the do-nothing option is that you start out cold, and you don't want to fuss with clothing, the radiant heater option would allow you to be warm to start, and then hit a kill switch when you start to warm up, rather than turning on the fans.

        1. _Stephen_ | | #9

          It's definitely a weird situation. If you don't run fans or heat, you end up both sweating too much and freezing! Weird eh?

          It's pretty normal to end up with freezing cold toes and hands, despite the heat, and still sweat buckets, literal puddles on the floor. Pretty much all the heat is generated by your legs, which happily gets pumped to your core, but then sweat ends up running down your legs to your toes and hands, where... now you have wet hands and toes at 5 degrees... It's pretty unpleasant.

          They do make cold weather biking gear, but it's not really built for indoor riding either.

          What most people end up doing is heating the space to some extent.

  3. Expert Member
    BILL WICHERS | | #3

    You'd need a 40A 240v electric circuit to run a 7.5kw resistance type electric heater. That's 8 gauge wire (unless you have a long run and need to upsize for volt drop reasons). If it were me, I'd probably run a 60A circuit (6 gauge wire) to a small subpanel in the garage. You don't add much cost going up once size in wire, and small 8 space subpanels are around $50-60 or so. The bigger circuit gives you some extra wiggle room for future needs at minimal increase in up front cost. If you need an underground cable run for a detached garage, this means trenching. I'd run PVC conduit for the power cable, and I'd install at least one 1" PVC conduit for future needs (like communication wiring). A second spare conduit would allow for future multiway switched outdoor lighting, which is a nice thing to have.

    If you have gas available in the garage, I'd use something like the Modine Hot Dawg heater. These are made for garages, they're vented, they're reliable, and they're easy to install and maintain. They also hold up well. I have had two of them in a greenhouse (which is horrendously harsh enviornment for a heater due to the high humidity levels). The first one died after a few years, but I found it was water running into the heater since the heater is under a bench. I had a stainless steel drip pan made to shelter the replacement heater and that unit is still going strong over a decade later. The ONLY thing I've done in the last 10-12 years with that heater was to replace the inducer (exhaust) blower, which I just did a few months ago since it finally died. The heat exchanger, and everything else, are still fine.

    In a garage, where you'll never have the constantly high humidity levels of a greenhouse, will be a much nicer place for a heater to live. I'd expect the Hot Dawg unit to last you a LONG time in a garage application.

    BTW, for a cyclic application like you're talking about, it's probably safe to just assume your heater is running the entire time you're cycling. That means 7.5kw times how every many hours you run it, so 3 hours 5 days a week means 3*7.5 = 22.5kwh/day, 22.5kwh * (5 days a week * 4 weeks a month) = 450kwh/month. If you pay 12 cents/kwh, that means $54/month to run that heater. You might find you run the heater longer to warm things up before you get there, but maybe let it cut out before you leave. The math works the same regardless, you just need to know your approximate total runtime to work out your operating costs.


    1. _Stephen_ | | #5

      Thanks for you input Bill.

      The natural gas heater I'm looking at would be the Mr Heater Big Maxx, which is incredibly similar to the Hot Dawg.

      The natural gas line runs right behind the wall where I'd want it mounted.

      I've gotten two quotes for installing it. One for $3600, and one for $1300. I've no idea why the quotes are so different. $1300 is quite stomach-able. $3600, less so.

      1. Expert Member
        BILL WICHERS | | #6

        Installation of these is pretty straight forward. You extend the gas line, put a shutoff and a sediment trap, then a short gas "connector" (the short, flexible gas line that goes to the appliance itself). You run some B vent from the unit to outside. You hang the unit (the steel angle with lots of prepunched holes is good for this, you can usually find it in the electrical department of the box stores). You need an electric circuit to run the unit.

        $3,600 seems very high to me unless you have something strange going on. Things that the high quote might include would be upgrading that gas line that "runs behind the wall" in case it's too small to handle the new heater. Gas lines are specced for flow in BTU over the distance of the run and the diameter of the pipe. More flow on a long run means you need bigger pipe. Chances are if you have a 1" or larger line you're PROBABLY OK, but you have to add up your loads to find out for sure.

        If the vent run is very long or has to pass through lots of things that could be a big cost. Normally you go either right out the wall or straight up through the roof. In a garage, this isn't usually a big deal.

        Electric is easy since the gas heaters only need enough power to run a few fans, maybe a few hundred watts (an amp or two) max. you can usually just tap them off of a nearby electric outlet circuit.

        I'd recommend you check the two quotes. It's possible that the high quote is just high, but it's also possible that the high quote includes something that the low quote missed. Sometimes a high quote is the result of a more thorough contractor that noticed something someone else missed so you want to be sure what you're looking at between those two quotes.


        1. _Stephen_ | | #10

          The line that is immediately behind that wall is the main gas line, about 4' from the pressure regulator. It definitely has some spare capacity.

          The venting should just be straight out the garage wall.

          I've since gotten another quote for $700, if I provide the heater, and do the thermostat wiring myself, which is honestly pretty trivial.

          1. Expert Member
            BILL WICHERS | | #12

            I'd go with the cheap quote then, just keep an eye on things - make sure you get a good install.

            Thermostat wiring in a garage is easy. Grab a cable tacker and some wire and tack the wire to wherever it needs to go. Most of those garage heaters just need a 2 wire thermostat, so it's super simple.


      2. T_Barker | | #28

        It can't be done for $1,300 in Canada. Maybe buy the unit and drop it off at your front step. You need electrical run, electrical shut off switch, control wires to the smart thermostat, gas line run, mount, and external exhaust. If they get permits - which you should get for this work - the ESA guy WILL show up, and you need a certified gas guy to do the gas work. Spend an extra few hundred for the upgraded unit and the heat exchanger will be better material (probably stainless), and if you keep the "non-working" temperature around 50F your unit will last for decades.

  4. Expert Member
    NICK KEENAN | | #8

    My first thought is what do you need heat for at 7C? Just put on a sweatshirt and a hat (or toque for Canadians).

    Now that I've gotten that out of the way, this is not a situation that normal heat load calculations envision, they expect keeping the interior relatively constant temperature. The way to proceed is with empiric testing. Around me you can rent a 150K BTU portable propane heater for around $15/day or $45/week. I'd rent one for a week when it's cold out, I think using it for a few days will give you a good idea of how big a system you need to do what you want and whether it's going to be practical.

    1. _Stephen_ | | #11

      Trying to dress for indoor cycling is uhh... challenging at best. You get sweaty, the sweat runs down to your hands and toes, and now you have wet hands in 7C weather. Which is pretty uncomfortable.

      They do make cold weather cycling gear, but it's not really made for indoor cycling either.

      Most people end up adding heat to the space.

      I like the idea of empirical testing...

    2. charlie_sullivan | | #13

      For the empirical approach you could also just put in a $30 1200 W space heater and measure the temperature rise: rate of rise and steady-state it reaches. Then scale up from there. If you want 3X faster rise, you need 3600 W, etc.

      But I still maintain that radiant heating is the perfect solution. I don't see any downside to that approach, which is cheaper and easier to set up, uses less energy, and helps the overheating and sweating problem, because you can ramp down the effective temperature instantly.

  5. _Stephen_ | | #14

    Reporting back!

    I tried Charlie's idea of throwing in a small heater to see the results.

    I can heat the garage to workable levels running a 1500 watt heater for three hours.

    I did however notice that I have exposed, insulated concrete for a 1' step along the bottom of my garage wall.

    I think I could easily cut some polyiso and insulate that. Would that buy me much?

    I'm also debating putting down some sort of garage floor tile. Would that have much insulating value?

    Given the efficacy of the low wattage heater, combined with adding the missing insulation, in going to go with an electric solution.

    1. tallpinescabin | | #15

      I have a similar situation. My 1940s 400 SF detached garage is not insulated yet, though. This past year, I jacked up and replaced the badly rotting walls and added gutters, so at least it's dry inside now. I ran 12/3 UF wire from the house out to a subpanel.
      For this season, I've been using (2) 1500W space heaters that I sometimes start ahead of time by 1-3 hours. But I also have been running a 100K BTU Propane torpedo heater for 5-10 minutes as well when I get into the garage to start riding. In my case though, the garage has been as cold at 15 F (-9c) when it was -9F (-22C) outside before I add heat.

      I find that 8-10C (46-50F) would be the ideal temp for much of my riding. Below 5-6C and my feet start getting cold.

      Just FWIW, sharing my plan after going through the same thoughts/calculations, and my experience with this year's heating situation....I plan to insulate the garage this year with R11 batts in the walls, and somewhere between R11 and R19 in the ceiling, and get the doors insulated with foam. (Are your garage doors insulated?)

      My thinking is that I'll install a 3KW Electric heater (Cadet Compak Twin), and then put in a timer to have it start up probably 1-2 hours ahead of time. Figuring I'll spend ~$20/mo in electric power for this setup, and the heater is relatively cheap. My hope is that I can heat the garage to 50 degrees F (10C) in the worst conditions. I looked at radiant heaters, but hard to find much that would be effective in the ~3KW range that isn't $800+. I can run the forced air heater for a LONG time to make up the price difference.

      1. Expert Member
        Peter Engle | | #17

        You could buy two 1500W radiant heaters for cheap...

        1. charlie_sullivan | | #18

          Yes, and with radiant heaters, having one aiming at you from each side does better at keeping your whole body comfortable.

          1. tallpinescabin | | #23

            While I see those ones linked above, I have suspicions that won't work well enough to be worth it for me in this case. One of my 2 1500 W Space heaters now is a radiant element design, and it's great for about 1/4 of my body in a cycling position, as far as radiant goes. I suspect it takes too many watts to create enough radiant heat to cover my whole body with the wattage I have available, and I definitely don't have the room for large tripods holding heaters on either side of my cycling setup.

          2. charlie_sullivan | | #24

            Nate, I'm curious what model the radiant one you have is. There are some that only put out a minority of their heat by radiation.

            And of course the amount of heat you need depends on how you dress. And if you dress to be comfortable starting out in a cold environment, you will overheat as your metabolism ramps up. Two solutions to that are to start with some extra layers that you can quickly shed. A loose fitting overcoat can be shed faster than clingy aero cycling clothes, and it's easier to do that on a stationary bike than it is outdoors as you don't need to stop and stuff the extra clothes in a bag. The other solution is to dress for a cold environment 20 minutes or so before you leave the warm house, so you start out feeling mildly overheated, and your metabolism kicks in to keep you warm just as you are cooling off from being in the garage.

          3. tallpinescabin | | #25


            Not sure it's this brand, but I have one of this type.

            Part of my issue is the radiant surface being physically long enough to warm my entire body...

    2. Expert Member
      BILL WICHERS | | #19

      Insulating that step won't hurt. How much it will help is difficult to say. If there is a lot of exposed area, then you'll probably see some benefit, but again, it's difficult to say exactly how much. I would look at it as a bit of an expieriment. you mentioned that you have "exposed, INSULATED" concrete though. If it's already insulated, you probably won't see any real benefit.

      Garage tile probably won't insulate much, if any, unless you've found a product that is specifically designed to have some insulating value. Everything I'm familiar with for this type of application is either a thin (1/4" or so) rubber or something hard (porcelain, etc.), neither of which really offer anything in terms of insulating value.

      BTW, for anyone reading this -- I HIGHLY HIGHLY recommend and can't say it enough: DON'T use UF cable for underground runs. Run PVC conduit and pull wire inside, and run a bit bigger conduit than you think you need. I usually use at least 1" conduit, since it's a sweet spot of cheap to size ratio. Conduit plus wires is often cheaper than UF cable, and gives you a little bit of future proofing. PVC conduit is cheap, and THHN wire is cheap too (compartively, anyway).

      There is no safety issue with UF cable, but it leaves you no options for upgrading without digging a new trench. You always want to avoid trenching when you can. I would always run at least 1" PVC conduit for power, larger if needed, and I'd always put in at least a 3/4" second conduit for communications wiring. The goal is to dig the trench once, and never have to dig again regardless of what you may need to do in the future.


      1. _Stephen_ | | #21

        I was under the impression it was insulated. I did not read the insulation plan very well.

        It's exposed, uninsulated concrete, for a 1' strip, the entire perimeter of the garage, about 75' long.

  6. Trevor_Lambert | | #16

    Southern Ontario is zone 6. Nowhere in Canada is zone 4. Victoria, BC is probably the warmest place and even that is barely in zone 5.

    1. _Stephen_ | | #20

      You are correct... My mistake. Zone 6.

  7. T_Barker | | #22

    For this application I'd probably install the gas unit heater. You want fast recovery, which the gas forced air heater will provide. $3,600 sounds about right. Any less and I would question the quality of work. They need a certified gas fitter to do the gas work, and depending on your current load in your house, sometimes they need to increase the gas line size all the way from the meter to meet code. Make sure they vent it properly, and don't let the fumes rise from under the eave into the attic!

  8. jhnmon | | #26

    Have you looked at ENERJOY Radiant Heat systems

  9. the74impala | | #27

    Are you willing to semi permanently transform the area? If so, why don't you frame a smaller area, with an insulated floor and walls and plywood over that and set up a bath vent to remove your sweat humidity? Easier to heat/ventilate a smaller, insulated area.

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