Expectations From In-Floor Heat

[HPRifleman]

The in-floor radiant heat systems are new to me but it looks like many of you feel that this the best way to heat a garage/workshop space.

After reading some threads on this forum I'm a little confused as to what the end result would be. I've seen some comments about being able to work in shirtsleeves in the winter but that doesn't seem possible from just a heated slab. I've also read about needing to plan your work in the area ahead of time as it takes some time for the slab to come up to temperature.

I am thinking about having in-floor heat for a 24' x 22' insulated shop area. This is also a room that might also have forced air heat. Can I expect to work in this room in the dead of winter with just a long-sleeve shirt on? If I'm in the room for a couple of hours, will my feet stay warm enough to be comfortable? For those of you that have the in-floor systems, are you happy with your ability to work in the space? Have you had to make compromises in the way you use your shop because of in-floor heat?

These questions are probably simplistic for many of you but as I said, I have no experience with these systems.

 

[brewchief]

Properly designed you will have no problem working in a t shirt.
You really need to plan if you don't want to heat it all the time or turn it down significantly .

I've got a friend with a 50x100 shop with a 25x35 shop area inside. The small shop is heated all winter to 62 degrees, you can walk in and work with a long sleeve t shirt at any time and if the lights are on for an extended period of time you will be down to a t shirt in no time(we have a LOT of t-8 6 bulb fixtures). Feet never get cold and the floor drys quickly ( we use the small shop for snowmobile work all winter and often will put 4 or 5 ice and snow covered sleds inside on a Sunday evening and by Monday after work they are completely dry).

Under slab insulation is a big deal and can't be skimped on, the bubble wrap **** is to be avoided as it's ratings are mostly smoke and mirrors.



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[DFB]

Oh man with rad under feet you'll be warm with ur boots on for sure

 

[jack stand]

Rifleman, tee shirt for sure. Just remember the insulation (do it right) , this is regardless of your type of heat. With radiant and good insulation including doing something about air infiltration, younu'll be able to set your temperature and forget it for the whole winter without spending a fortune. Once you're slab is up to temperature, it takes very little to keep it there (that's the insulation part) . The vehicles, tools, jacks, everything (including your 25,000 pound slab) is up to temp, turning it down for the night or the week may not save you a penny and of you insulate properly, it could be argued that it would actually cost you more setting back the thermostat.

 

[Rc_Guy]

The house and garage in my avatar is heated by in floor heat only, my garage is at 65° And the house about 71°, I can walk barefoot in the garage and don’t need a jacket at all.

 

[stingry]

Rifleman, tee shirt for sure. Just remember the insulation (do it right) , this is regardless of your type of heat. With radiant and good insulation including doing something about air infiltration, younu'll be able to set your temperature and forget it for the whole winter without spending a fortune. Once you're slab is up to temperature, it takes very little to keep it there (that's the insulation part) . The vehicles, tools, jacks, everything (including your 25,000 pound slab) is up to temp, turning it down for the night or the week may not save you a penny and of you insulate properly, it could be argued that it would actually cost you more setting back the thermostat.

I agree 100%. I’m into my second season of radiant floor heat and am convinced that it is the best possible heat for my application. My shop is 3600 sq ft with 10 ft walls and costs me around $100 a month to heat here in western Nebraska. I use air temp thermostats and keep the temp at 65 degrees at eye level. It is as comfortable as our house at 72 degrees. Shirt sleeves for sure.

I keep it at the same temp all winter long. No noisy fans coming on, blowing dust around and I feel no variation in temps that you do with an overhead heater. One other thing, when you open an overhead door and close it, you feel immediately feel warm in front of the door! As said above, with a properly designed radiant floor and good insulation, you can’t go wrong.

Cheers
Steve

 

[walrus]

I was doing a job at a earthwork contractors maintenance facility. Big building, at least 25 ft ceiling, block building 5 or 6 huge over head doors. I was working outside on fuel equipment for a couple weeks. Every time I came in to use bathroom I noticed how warm it was. Of course I was outside so it would feel warm but this was different. Finally I was told it was radiant heat thru out shop.

 

[flippin]

I am enjoying radiant floor heating in my new garage addition (12x40). I'm in Canada and we've already had several days below 0 Fahrenheit still always t-shirts and barefoot. The heat is awesome and everything on the floor dries so quickly. I also installed a Mitsubishi mini split with a heat pump. Primarily for AC in the summer, but it also quickly warms the room up if I lower the thermostat for the radiant. I'm still figuring out what works best for me, but regardless I love the radiant and would encourage you to install a boiler to cover your radiant and domestic hot water.

Good luck,
-Paul

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[Mancino]

I think it really depends how warm you will keep the space. My shop is set at 50°. I definitely don't work out there in a tee shirt unless its strenuous work. I have a few radiant zones in my house that are set to 65°. Now those are great for walking barefoot!

I will say what I have noticed is really great about the shop radiant is when you open the OHD. I can pull a car in/out and the heat doesn't kick on...or if it does, it's for about 2 mins until the temp comes back up. The recovery time is super fast because the slab is a giant thermal mass so it just releases more heat into the room as the temp drops. You won't get that same effect with a wall hanging unit.

 

[Redraptor]

I have a 950sq/ft short pole building that I heat. I keep the temp at 55* as I'm not insulated well enough under the concrete. But the temp is even in every corner and my simple unit has no trouble maintaining it. I am comfortable working in sweatshirt. But like my basement if you sit for 10 minutes you get chilly. I just installed a Mr. Heater Big Maxx to bring the temp up to 70 if I'm out there for extended periods or sitting with friends at my mini bar, otherwise it's shut off.

 

[Jackfre]

As you move forward with this consider adding a bit of radiant about the length of a vehicle in the apron outside your doors. Being able to melt and dry that area is really nice. Run it on a separate zone.

 

[HPRifleman]

The house and garage in my avatar is heated by in floor heat only, my garage is at 65° And the house about 71°, I can walk barefoot in the garage and don’t need a jacket at all.

That's incredible! My experience with garages in winter is seeing my breath and avoiding working in them.

Rifleman, tee shirt for sure. Just remember the insulation (do it right) , this is regardless of your type of heat. With radiant and good insulation including doing something about air infiltration, younu'll be able to set your temperature and forget it for the whole winter without spending a fortune. Once you're slab is up to temperature, it takes very little to keep it there (that's the insulation part) . The vehicles, tools, jacks, everything (including your 25,000 pound slab) is up to temp, turning it down for the night or the week may not save you a penny and of you insulate properly, it could be argued that it would actually cost you more setting back the thermostat.

Understand about the insulation. I certainly want to do it properly if I went radiant. I like the idea of being able to leave it on all winter as I would probably want to be out there for only an hour or so at a time, and I don't want to have to plan ahead.

I am enjoying radiant floor heating in my new garage addition (12x40). I'm in Canada and we've already had several days below 0 Fahrenheit still always t-shirts and barefoot. The heat is awesome and everything on the floor dries so quickly. I also installed a Mitsubishi mini split with a heat pump. Primarily for AC in the summer, but it also quickly warms the room up if I lower the thermostat for the radiant. I'm still figuring out what works best for me, but regardless I love the radiant and would encourage you to install a boiler to cover your radiant and domestic hot water.

Good luck,
-Paul

The existing space has forced air heat/cool because the water pressure tank from the well is located there.

My original plan was to keep the forced air as a supplement to the floor radiant as I thought that just heat from the floor would not be enough to comfortably heat the space. Judging by everyone's comments, I could heat the room fine with only the floor. Looks like the forced air would be a bonus for the winter and be able to cool in the summer.

 

[finn]

I have in floor radiant in my shop office, bathroom, and 32x75 workspace in the main building. The building has 16’ ceilings, insulated walls and foam under the slab and around the perimeter. Also, two man doors and a 10x14 and a 12x14 insulated overhead door.

The boiler is 96% efficient condensing propane unit.

It’s expensive to heat. Over 750 gallons of propane last year, keeping the stat at about 46 degrees and bumping the temp to 60 when I am working. 60 is a comfortable temperature because your feet are warm.

I typically work in the shop a few hours per day, maybe three or four days per week, so most of the time the shop is at the base temperature setting.

My house has radiant in floor (staple up). It works well, warm floors, etc, until the temperature outside is below -10 degrees for extended periods. There is too much heat loss through the vaulted ceiling and glass wall relative to the floor radiant area , so I have to use supplemental heat during extended cold snaps.

My HVAC guy had this discussion with me. His own house has radiant with an outdoor wood boiler, but he told me that my experience is not atypical in our ares. Radiant had a fairly long run in popularity in new construction for both homes and shops, but popularity has really dropped off over the past ten years or so.
I would have to think long and hard before I did a new building with radiant

 

[ScaldedDog]

As one about to give up a radiant floor heated garage for a radiant tube heated barn, I can tell you I'm going to miss the floor heat, badly. Mine is a 6" slab on top of 2" of DOW HILOAD insulation, and kept at 58* all winter. I've found it dirt cheap to heat, but the garage is built like a tank and well insulated. I start out wearing a jacket in the mornings, but if I'm at all busy I'm down to a t-shirt before long. I never think about it, but realized as I'm writing this that one of the best things about it is that nothing you pick up or touch ever feels cold. I wish the owner of the property we are buying had at least insulated and run PEX, both in the garage and barn, as I'd surely take advantage of it.

Mark

 

[Randy in Maine]

My 28x40x12 foot shop is built out of R-40 SIPs and I keep it at just 50º air temp all winter. Long sleeve shirts work for me. Plenty comfy.

I do have a 35-85K propane (BBQ tank) salamander out there, but I have never used it.

 

[DFB]

Catherdral ceilings and large amounts of glass are difficult to efficiently heat under cold conditions no matter what.

I remember how my old restored farmhouse in up Maine had a 16ft to peak cathedral ceiling and huge window of glass. We had an extended cold snap one year stayed below zero constantly for over two weeks straight. I was burning wood my major heat source for that house. If you got up high to that ceiling it was probably close to 100F up there but was still cold by floor, and of course the floor was always cold too so again doesn't help much if your feet feel cold. Without heavy rugs or socks and shoes. Went thru massive amounts of cord wood that year

I have under floor staple up radiant with an oil fired boiler for the newer house here in Vermont. Been 13 years with it now. I also have a lot of glass I would say almost a good 40% of my front house wall is glass tall double insulated draft free windows. That is a large heat loss no denying, glass is not a very efficient insulator at all. In retrospect and being cheap in my old age I would probably use less glass if I ever designed a house again

Still the house is plenty warm with under floor radiant because I do have standard ceiling heights and is well insulated. I keep it at approx. 68 but have no problem making it warmer well up into the 70's if needed even under below zero temps.

With my system I did do some experimenting and some consulting with some "local" installers bumping up the water temp some thru the mixer valve over minimum recommendations but still staying under max high temp recommendations. It really does help.

Also as someone else pointed out earlier it is the overall mass your heating keeping the system at constant temperature is far better and more efficient IMO anyways than turning it up and down. Cool the house down and depending on ambient outside temps it can a quite a while to really feel comfortable again.

I like to check my lines floor temps across the house with temp gun Gives me warm fuzzy feeling

But I wouldn't have any other way now. My latest GF rents a big old renovated farmhouse for the ambiance lol! Not at all effiecient to heat...the costs are phenomenal.

 

[yeldogt]

BTU's are BTU's __ radiant heat is not really for saving money. 50 degrees -- is 50 degrees .. if you are cold at 50 degrees you will be cold with a room heated with radiant at 50 degrees.

What radiant does is allow for placing heat where your body most needs it -- with high ceilings and good insulation the upper level will actually be colder than at your head level. This is not possible with forced air heat. This will save fuel vs other types of heat ... radiant also often will allow for a bit lower temps .. again, because the heat is at body level

The key with radiant is the same with any other building to make comfortable --- good insulation and air sealing. A properly insulated slab in a conventional building can be comfortable as long as temps are maintained. A concrete slab is high mass -- it takes many BTU's to heat. This is why a conventionally heated garage (hanging modine type heater) can often feel cold if the temp is not maintained. It takes many hours for the rooms air to finally heat the slab .... it may never if the heat is only on for a few hours. The room has a cold sink (the slab) -- pulling heat from your body. It's not that slabs have to be cold -- they are because they take lost of BTU's to heat.

The speed a slab will heat is dependent on the thickness -- start temp and amount of tubing. This is why if you plan on trying to change temps often -- you need more tubing closer together. Closer tubing = more BTU's going into the slab. I do 6"or 8".

I have a friend with and old leaky building (it's an old barn)... uninsulated slab w/ radiant -- and a wood boiler ... he owns landscaping business and the wood is endless. The space is warm .... the ability to work in short sleeves is all about BTU's going in. My friends BTU's are basically free .... you would not want this system if you were paying for the fuel.

Radiant heat has an output range -- what you can get out of a staple up system is going to be less vs what you can get out of a slab. A slab does not care how hot it gets -- it's determined by the comfort of the people standing on it. A previous poster mentioned staple up -- this is where PEX tubing is placed (stapled) under the subfloor -- it has a limited heat transfer ability. Even at 180 degree water there is only so much transfer possible ...often this number is not enough to provide the heat needed for the space in cold weather. A slab will keep heating ...

A slab does not have that problem -- I have been in uninsulated loading docks with radiant and the floor is hot and people warm .... it's expensive.

My all glass sun room is heated with radiant --- obviously the temp of the floor is higher vs the kitchen that is open to this room .. but not all glass.

OP: with the ability to have forced air as well -- best of both. You can pick a temp that warms the floor -- this may or may not provide all the heat needed when it really gets cold ... but you then have the forced air to make up this small difference. The slab stays warm.

In a well insulated building a typical floor never gets overly hot ---- I have a couple panel radiators in my glass room. When the temps drop under around 15 degrees -- I don't like the floor temp. It's too hot for me ... some have no problem .... but I find that limiting the floor heat temp and providing the extra another way is more comfortable

 

[86turbodsl]

As someone who struggles mightily with keeping his feet warm in winter, and productivity is directly related to that with me, radiant has been a godsend. I'll never have a shop in cold weather again without it if i can help it.

 

[Specracer]

Short sleeves will depend on your set point. Our 50x70 has radiant, and I love it (been ~10 years). Couple things, we did supplemental heat, never used it, set at 60-62, and is good to go. Remember, a change at the t-stat, will take a day or so to happen. Lack of dust, amazed how the lack of air blowing around, mitigates dust. The heat is in the slab, so that when you open the door, the temp of the room stays very stable. Also remember the threads about a creeper vs cardboard? W radiant and a clean floor, you will be happy with neither.

 

[PWC Repair]

I have radiant floor and a forced air hot water fan coil. I got my system up and running too late, slab temp is too cold for my btu's to catch up without constantly running. I'm using a 50 gallon electric water heater that only kicks on one 4500w element at a time. That's about 18,000 btu. My fan coil can cycle normally 3 times before the water heater has to kick on. Been keeping my 30x40x12 open span shop 50* for an average of $2 a day. Worked down in the shop all day today so bumped it up to 58. So far so good.

 

[Ak Jim]

Keep mine set to 67. The flooor temp at -40 is 73. Very nice place to be.

 

[HPRifleman]

Keep mine set to 67. The flooor temp at -40 is 73. Very nice place to be.

That temperature differential between your floor and outdoor is amazing. I guess if it works in an Alaskan winter it will work in my area.

 

[finn]

M shop floor is about six or seven degrees above the thermostat set point in extremely cold outdoor conditions, say in th teens or below..

The temperature difference drops as outdoor ambient temp rises.

It’s all about thermodynamics and heat transfer, and in floor follows the same laws as every other heat source.

Many in floor system installations take care with slab, door, wall, and ceiling insulation to reduce heat loss to the environment. That’s where the savings is. Its not a magic system. A 96% efficiency boiler is just as efficient as a 96% furnace. No more.

All the fantastic claims of low operational cost are tied to insulation, not pex tubes in the floor.

 

[yeldogt]

That temperature differential between your floor and outdoor is amazing. I guess if it works in an Alaskan winter it will work in my area.

There is nothing amazing about it ..... it's just heat (BTUs)

The floor is nothing more than a radiator ..... Just like that big old cast iron thing in an older victorian house. Pump hot water into it ... it gets hot.

Hot objects ... radiate. Just like the sun on a cold day -- a fire at night.

Hot air from a furnace -- does not.

 

[pbrsucks]

Does anyone use a heat pump with the heated floor or just water heaters? If so does it help cool the space in the summer?

 

[finn]

There was a thread maybe six or ten weeks ago where someone said heat pump radiant installations were available in Europe, and that one manufacturer, perhaps Daiken? previously offered them here, but they withdrew the hardware from the market a couple of years ago.

 

[jack stand]

It’s all about thermodynamics and heat transfer, and in floor follows the same laws as every other heat source.

A 96% efficiency boiler is just as efficient as a 96% furnace. No more.

All the fantastic claims of low operational cost are tied to insulation, not pex tubes in the floor.

I'd agree, but the warm slab radiating heat is a far cry from just warm air (furnace) going past you on the way to the ceiling.
Can't comment on overhead radiant gas tubes, but there's no comparison to my past hanging "modine" heaters and ceiling fans blowing my warm air back down (that felt like a cold draft) from the 16' ceilings in actual comfort at much lower temps.

 

[86turbodsl]

Does anyone use a heat pump with the heated floor or just water heaters? If so does it help cool the space in the summer?

I do in my house. GSHP / radiant floors. You don't use the floors for cooling. Too easy to hit the dew point and ruin the expensive wood. I have a water source air handler for summer air conditioning and rooms without radiant.

 

[HPRifleman]

Just to clarify, I wasn't looking to work in the garage in a t-shirt when it's -10 outside. But I would like the benefit of being in something that feels similar to an indoor conditioned space. I have worked in the winter in heated shops but there was still something that made them feel drafty with uneven heat. They probably lacked insulation but I suspect standing on a cold slab also had something to do with it.

Thanks to everyone that responded.

 

[Sevenhills1952]

My grandfather next door and Dad built parent's house in 1948. Mom still lives there. Dad had never soldered before, grandad showed him how. They formed up and poured concrete slab, home is cinder block, about 1500 sq ft, story and half.
Dad said he used copper tubing (3/4" I think) and went up...few inches over, back, etc. It's always had fuel oil furnace and boiler. It has original flooring, they used looks like ft square linoleum tile. The floor has never cracked, never had a leak. There are small radiators upstairs for bedrooms and bath. What I like is it's quiet. Off the enclosed porch is the "furnace room", down maybe 4ft. Door, landing, few steps.
Heat is very even. No drafts. It's interesting it can be zero outside, shoes off inside walking on 72 deg. floor.
I don't know the efficiency but it's an interesting and nice heat.

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[rburke65]

You need to keep reading the comments on here about the radiant heat.

 

[stingry]

Just to clarify, I wasn't looking to work in the garage in a t-shirt when it's -10 outside.

There’s no reason not to expect this level of comfort as long as it is properly insulated and the radiant floor and associated heat source is properly designed!

We had a Christmas blizzard, temperatures in the single digits and 50+ mph winds, my shop interior temperature of 65 degrees didn’t vary a bit.