Under floor heat... is it really that great?

[WI/MI Border]

This is a inquirey about my future garage/workshop monolithic slab (floating slab). I may might not be doing an apples to apples comparison, but, my 70s built ranch house does not have insulation, vapor barrier or heat under the floor. I'm talking the basement floor. No moisture problems. The floor is cool to cold to bare feet but comfortable with footwear. Now I am going to be building the garage/shop this spring. I have a plan to put down vapor barrier over the compacted sand base. Otherwise it will be rebar and concrete and perimeter monolithic slab insulation only.

I hope to put in a mini split of at least 18K BTU, maybe a 24K BTU (a DIY install between $1k and $2K). I will also be building a RMH in the shop. If you are not familiar with Rocket Mass Heaters they are a wood burning masonry heater that burns for a couple hours to heat mass (masonry) and release the heat over a matter of hours. I'm on the WI/MI border so we get cold weather here. Maybe up to ten days of sub zero F at night. January and February average low temps in winter is 5 to 7F degrees, average high temp is 25-30F. Between the mini split and RMH I should be plenty warm while working in the shop.

When I'm working in the shop my feet will be fully clothed in warm footwear. I won't be crawling around on the floor very often. I'll probably start off with the mini split running full time at about 50 degrees and raising that temporarily prior to occupying the space. Let's just ignore the AC portion of the shop and mini split. I have central air in our home and don't use it. It hasn't been turned on for over two years. It was installed when I was working graveyard shift and needed some AC to get some sleep. Again, WI/MI border. Many here depend on AC. Me, rarely.

So, what is the real advantage of in floor heat? I haven't looked into it seriously because of the cost of installation, efficiency and slow recovery time (50 degrees to 65 in hours rather than minutes with a forced air system. I'm expecting some push back on those assumptions. If you have a different experience with in floor heat and an insulated slab please let me have it! : ) If you have a well insulated shop and use a mini split please chime in and let me know how it works.

The plan
24x28 with nine foot ceilings. 2x6 walls (R19), Blown in ceiling insulation (R30), 9x7 garage door (R18), three double glazed windows, two insulated doors.

 

[whateg01]

I can say that working on the floor of Dad's shop, a not freezing floor is pretty nice. It also seems to keep the shop temperature pretty steady. But, it's always running and can't warm up a space in 10 minutes. Mom said a couple weeks ago it's costing a fortune to heat the shop this year. I don't know what it normally costs or what it is actually costing now, but that was her comment. That's all the experience I have with them. I had always thought I wanted one, but now I wonder if it wouldn't be ok to have a heated floor just to keep the floor not freezing cold but a regular heater to make the workspace comfortable.

 

[STINEY]

I thought long and hard about the same topic.

What I came up with was - insulate with 2" 250 foamboard under the slab, to separate the slab from transferring the ground temp as quickly. (this also keeps my floors from sweating on those huge temperature swing days in the spring - a real big issue in Ohio)
My floor isn't freezing cold and the thermal mass holds its natural temp much longer than the unsinulated floor in the other part of the barn just a few feet away.

Use a mini-split system. I don't worry that mine is technically undersized for the job - who wants it 70 degrees when working in the shop anyways? 50-60 is more than fine. Its not a house after all.

The mini-split will also perform the function of removing humidity. Something a heated slab is rather ill-equipped to do. (again, humidity is a large issue in Ohio. It ain't the heat, its the humidity - that's no joke.)

Works for me, and I didn't have to buy two different systems. Operating costs are reasonable as well.

 

[4x4Pete]

Infloor radiant heat is, in my opinion, way overkill for a working shop. Radiant tube heat provides almost the same benefits without having to deal with the expense of a infloor system. In my case I could have put anything I wanted for hvac in my shop, I was in the trade for 30+ years. I chose a radiant tube heater. Superior Radiant Systems. I didn't want forced air (loud and messy unless proper duct work is installed) I didn't want expensive (infloor radiant with piping, pumps, boiler, fill station, etc...) I find the radiant tube to work very effectively as long as the temperature is maintained. Just like infloor, you can't warm the room up too quickly. Faster than infloor but still not as fast as forced air. Perfect for a working shop.
My shop is 30x32x12. The slab is monolithic 6" thick throughout. Thickened to 20" around all sides. 2" 30psi foam underneath with 6mil poly vapor barrier, the outer edges are insulated with the same foam with 24" wings to help keep the frost out. Not that I let it freeze.

 

[Rc_Guy]

I’m in Minnesota, I have in floor heat in our pole barn house.

One zone in the house, the other zone in the garage. Just runs quietly keeping the garage and house warm.

Don’t even have a furnace, mini split for A/C.

 

[STINEY]

I concur with 4x4Pete. I would have done radiant with a simple dehumidifier - IF I had access to natural gas.

I do not, propane is too pricey, so the mini-split fit the bill for me.

(and I would do evil things to have natural gas. I envy those who have it.)

 

[WI/MI Border]

I’m in Minnesota, I have in floor heat in our pole barn house.

One zone in the house, the other zone in the garage. Just runs quietly keeping the garage and house warm.

Don’t even have a furnace, mini split for A/C.

Thanks. I get that in floor heat is a good option in a home. You don't set it at 50 and only raise it when you are home. It just wouldn't work for variable temps like I suspect I'll have. In a house it's probably wonderful to have warm floors!

 

[Wrench97]

A buddy has one, recovery time after opening the door is long. if you don't have to open the door my feet sweat and my head is cold.
The opposite of normal for me

 

[LopezBart]

Underfloor heat is lovely in our house. I decided not to go for this in our shop, due to expense. I'll likely use a minisplit for heat (cooling isn't needed in our climate) to keep the place from freezing.

 

[whateg01]

...
Use a mini-split system. I don't worry that mine is technically undersized for the job - who wants it 70 degrees when working in the shop anyways? 50-60 is more than fine. Its not a house after all.

Screw that! I want it 72-75 in the shop unless I'm doing something that is labor intensive such that I'll be building up a sweat. In the summer I run the AC (will be a mini split by next summer) and keep it 72-75 also.

 

[dscheidt]

Infloor radiant heat is, in my opinion, way overkill for a working shop. Radiant tube heat provides almost the same benefits without having to deal with the expense of a infloor system. In my case I could have put anything I wanted for hvac in my shop, I was in the trade for 30+ years. I chose a radiant tube heater. Superior Radiant Systems. I didn't want forced air (loud and messy unless proper duct work is installed) I didn't want expensive (infloor radiant with piping, pumps, boiler, fill station, etc...) I find the radiant tube to work very effectively as long as the temperature is maintained. Just like infloor, you can't warm the room up too quickly. Faster than infloor but still not as fast as forced air. Perfect for a working shop.
My shop is 30x32x12. The slab is monolithic 6" thick throughout. Thickened to 20" around all sides. 2" 30psi foam underneath with 6mil poly vapor barrier, the outer edges are insulated with the same foam with 24" wings to help keep the frost out. Not that I let it freeze.

I detest tube heaters in a shop. Push a dead car in from the frozen lot, put it on the lift, and stand under it. The top of the car gets warm, you don't. The snow on the roof melts, and drips on you. It *****. It's fine in a machine shop or a wood shop, or whatever, where you get under cold things all day, screw that.

 

[WI/MI Border]

So in floor heat has its place. In a home or other space where the desired temperature is mostly constant. I had to ask because for the past few years friends and acquaintances have mentioned in floor heat as the way to go without expressing reasonable facts about it's use. It seemed to be the new, cool way to heat their space. I'd be interested in how they feel about it now after years of use. I would pursue that opinion, but I'm going to stick with my plan.

 

[theoldwizard1]

So, what is the real advantage of in floor heat?

COMFORT !

If your feet are warm, you are warm !

 

[Tundra1]

Are there any localized heating pads that would hold up to shop use? Seems like a 3'x4' floor mat would be really nice at a workbench and not require the whole slab to be toasty.

 

[flippin]

I built the shop and installed radiant floor (natural gas boiler) as well as a mini-split. Wish I had this in the whole house. Everyone is different and we like what we like. That said, I would be curious how many persons have radiant floor in the shop and regret having done so? If you are concerned about the initial costs, just install the foam board and pex tubing with the option for a boiler afterwards. Our boiler provides all of the domestic hot water as well as radiant floor in the shop.

I am in Ontario, so our climates are pretty similar. Whatever you do, be sure to install a minisplit for A/C in the summer. I play with tackle on my boat all summer with doors closed and no mosquitoes.

 

[Kezorm]

Wouldn't be without it in my shop in Minnesota. Silent. Comfortable. Keep it at constant ~50F throughout winter. Put on sweatshirt if not working hard. Take off if building up a sweat.

Not sure I understand the earlier comment about slow recovery after opening door? Recovery is extremely quick because of all the heat stored in the mass of concrete. I can open the door in -20F weather and be back to comfortable within minutes after closing the door.

Previous garage / shop experience was a hanging natural gas heater. Loud, drafty, hot / cold spots, cold floor, etc. No way would I ever go back.

Greg

 

[flippin]

Not sure I understand the earlier comment about slow recovery after opening door? Recovery is extremely quick because of all the heat stored in the mass of concrete. I can open the door in -20F weather and be back to comfortable within minutes after closing the door.

Previous garage / shop experience was a hanging natural gas heater. Loud, drafty, hot / cold spots, cold floor, etc. No way would I ever go back.

Greg

This exactly, unless you plan on only turning on the heat when you want to work in the shop. Certainly radiant is much slower to get the whole place heated to a comfortable ambient temp. If you do not plan on always heating the shop, then perhaps radiant may not be the option for you.

 

[LopezBart]

This exactly, unless you plan on only turning on the heat when you want to work in the shop. Certainly radiant is much slower to get the whole place heated to a comfortable ambient temp. If you do not plan on always heating the shop, then perhaps radiant may not be the option for you.

Yup.... floor heat systems are ill-suited to 'turn-down' thermostats. If your climate requires heating or cooling much of the time, and you spend a lot of time in the shop every week, floor heating/cooling might be perfect for you.
If on the other hand you're not in the shop every day or every week, I'd probably select something else.

 

[Bert_]

Screw that! I want it 72-75 in the shop unless I'm doing something that is labor intensive such that I'll be building up a sweat. In the summer I run the AC (will be a mini split by next summer) and keep it 72-75 also.

Wow. I can't imagine 75 in a shop. 55* is nice and comfortable!

 

[WI/MI Border]

Another hot topic on online forums! Wow, I didn't expect that. Anyway, I'll do me, you do you and we'll all live happily. : )

On to something else to chat about. I think I'll go with mini splits in a new topic.

 

[PoorUB]

Screw that! I want it 72-75 in the shop unless I'm doing something that is labor intensive such that I'll be building up a sweat. In the summer I run the AC (will be a mini split by next summer) and keep it 72-75 also.

I have worked in shops with forced air heat, radiant tube heat, and floor heat. In my opinion, floor heat is by far the most comfortable. With floor heat you feet are warm and the heat rises up to you, You can run the room temperature 5-10 degrees cooler and be more comfortable that you would be with forced air.

Overheat infrared tube heat is fine, but does nothing for you if you are working under a car, or get out from under the range of the heater. You can stand right under the heater and melt the top of your head and walk ten feet away and be cold.

My first preference would be floor heat without question.

 

[larry_g]

What sells floor heat for me is that the tools in the shop are warm. The mill, lathe, and wrenches in the drawer are all warm to the touch. I hate grabbing cold metal. The cast iron large tools for metal working or wood working take a long time to heat up and be comfortable to touch. Warm tools do not support the condensation of moisture out of the air. Like said above the warm floor and cool air make for a comfortable work area. Hot air and cold tools not so good.

lg
no neat sig line

 

[fitter30]

Air is easy to heat. Mass is the hard part. Plan on working on a car without a lift? Floor heat your **** will be comfortable. Thinking about setting temp back when not in use for a day or longer it might take 2-3 days to get caught up. One to heat the slab and then the mass. Had radiate electric heat under tile and a area rug in a family room. There is nothing like when its freezing working out in the cold all day coming home laying on the floor its heaven.

 

[Rc_Guy]

Screw that! I want it 72-75 in the shop unless I'm doing something that is labor intensive such that I'll be building up a sweat. In the summer I run the AC (will be a mini split by next summer) and keep it 72-75 also.

We keep our garage at 70°and keep the door open to the house and go back and forth between the two.

 

[Jackfre]

I can buy all the material at wholesale pricing, have done tones of it over the years and when I built my 1000 sq ft shop I chose to put in a Rinnai EX-38. My MA garage I had a Rinnai blowing heat under the car. Nice while on a creeper welding in floor pans. You have the climate to use radiant to good effect and it really is great heat, but not fast, not cheap either in install or operation. If you have the dough, time and jsut have to have it, go for it. I chose to buy tools for the shop rather than the radiant.

 

[Mattilac]

As someone who has ice cubes for feet all winter (it's awful, I don't wish it on anybody), I can't wait to get my garage finished and radiant heated slab turned on! Hoping it will be life changing.

 

[i4ni]

We have electric floor heat under our main level tile floors but don't use it much because of cost for one and the fact that they suggest not to keep entry mats or rugs on it. Mother-in-law has in floor tube heating in her basement and her 3 car garage on separate zones. She keeps her garage at about 55. Amazingly the main level benefits greatly from the radiant in the basement and her propane use is actually less than mine. If I were to build a new home I would definitely go radiant tube floor heat.

 

[Mr onetwo]

This is a very interesting discussion. I have a propane tube heater in my present shop with R19 fiberglass in the walls and ceiling, 16x8ft R16 door.Although I keep it at 50 degrees all winter, it uses a lot of fuel.I do like the nature of the heat, but I am getting more sensitive to the unheated floor as I age. I am starting a new build on my new 30ac property and this is front of mind. I am thinking about a radiant floor fed by a combination of solar and propane for the winter months, a split for spring and fall + cooling and some sort of spot heater for localized needs and picking up the temp in the space after I open the 16x10 door. I am thinking about a 40 gallon dual coil tank fed by a combination of a couple of hydronic solar panels, propane boiler and electric boiler w/ panels. I plan on enough solar panels to help with the cost of cooling and heating and provide backup during outages. I already have a EG4 inverter,battery and Viessmann boiler on hand. Sounds complicated, but HVAC was my trade for 40 years and solar isn't hard to figure out.Then maybe a diesel spot heater...I am open to suggestions on that. One last thought...infloor heat does not work well without high insulation values and great air sealing of the structure.

 

[4x4Pete]

I detest tube heaters in a shop. Push a dead car in from the frozen lot, put it on the lift, and stand under it. The top of the car gets warm, you don't. The snow on the roof melts, and drips on you. It *****. It's fine in a machine shop or a wood shop, or whatever, where you get under cold things all day, screw that.

What is the difference? I have worked in a dealership where they had forced air heat. When you bring a frozen snow covered car (or just a frozen driven car for that matter) into the shop, they all drip and soak you. I think working on cars as a job in the winter *****, regardless of the heating type.

 

[mas1]

this is our 2nd year in our new home. Garage is 50’ wide x 57’ deep with 19’ ceilings. Garage is attached to house.
northern Wisconsin. In floor heat throughout. 3 zones in the garage. Regardless of what ever heat system you use, pay attention to the insulation system. Our entire structure is on a monolithic slab with grade beams. The code is very specific regarding sizing and insulation requirements. A huge benefit is the insulation that is not only placed under the slab, but also along the outer edge, down the grade beam and then running out horizontally. this helps to keep the frost from hitting your concrete.
Rockwool insulation in both the walls and ceiling and blown in additional in the ceiling. Big overhead doors, pay attention to the side and top seals, you would be shocked to see the terrible job the standard exterior seals due, especially with the wind blowing.
We don’t touch the thermostats. Garage set at 55, house set at 65. Doesn’t matter what the outside temp is, extremely comfortable.
we also have huge windows that take advantage of the solar benefits.
total of 7100 sq.ft. Since April of last year, I purchased less than 700 gallons of l.p. We also have a gas cooktop and water heater.

 

[HoosierBuddy]

I put infloor heat in my garage build in 2006 and haven't regretted it too much.

I will say that it does take a bit of annual maintenance.

If you are dead set against putting insulation under your slab, then DON'T put in loops. The insulation is part of what makes it work well. That being said, I could see advantages to insulating under your slab regardless of how you plan to heat it.

For intermittent heat or where you want to use a large setback temperature when you aren't out there, in floor is not the best choice. You'd be better off with forced air gas, like a hanging gas heater.

If you are going with a gas heater, I'd always push to consider hi efficiency ones, like the modine effinity line....BUT if you are going to want to turn off the heat during the winter you can't go that route because your condensate line will freeze. If you want part time heat, I'd still go forced air gas but then I'd get a less expensive non-condensing unit.

This really is a case of "There is no correct answer unless you know how you are going to use the garage".

Based on what I'm reading....in floor heat would not be my first choice for your situation and intentions.

 

[Bert_]

Tube heaters do warm the floor. Not in the whole shop but it's a surprisingly large area.

At work I keep the shop 50 at night and 55 if we are around during the day. The floor is about 75* under the heater.

It's very important to put a tube heater where you will be the most. If you put a tube heater next to the far wall in your shop, you will probably be disappointed. Sometimes (2) smaller heaters are better than one big one.

 

[PoorUB]

I have a friend with a shop with over head infrared. In the morning all his workers are huddled under the heater. You can walk 10 feet away and it is very noticeable that area is much cooler. Granted the shop is probably 40 feet wide and he ran the heater right down the middle. Floor heat will heat the whole room, where ever you put tubing, An infrared will heat the whole space too, but it will be nice and toasty under the heater and as you walk away it will get cooler.

 

[kabinenroller]

I’m in SE Wisconsin, my shop is 2,400sq ft, I live in a semi remote area with no gas, cable, etc. I have hydronic heat in my shop that is pushed by a LP wall mounted boiler. I wouldn’t consider any other type of heat, everything in the building is the same temp, from tools in the drawers to the pictures on the walls, quiet, clean, takes no space. Spend the money once and enjoy the comfort.

 

[lovetap]

24x28 is a small enough space that it wouldn't be too much extra work to install pex at tight intervals like 6-9" which anecdotally seems to help with reaction time. I just completed a 640 sq ft with radiant slab at I'm very happy I did so. My dad's place is overhead forced air like a Modine, and while it gets the air back up to temperature decently quick after bringing a cold car inside it takes forever to get the car itself warm.

Don't need to restate the posts above, but I also find the garage retains it's heat really well after opening the garage doors due to everything radiating. I can bring in a frozen objects and just lay them on the floor and they are thawed in no time. I also leave my temperature lower because it "feels" warmer at a lower air temps than forced air. I wouldn't hesitate to insulate, vapor barrier, and install pex in any future slab just so I had the option.

 

[WI/MI Border]

24x28 is a small enough space that it wouldn't be too much extra work to install pex at tight intervals like 6-9" which anecdotally seems to help with reaction time. I just completed a 640 sq ft with radiant slab at I'm very happy I did so. My dad's place is overhead forced air like a Modine, and while it gets the air back up to temperature decently quick after bringing a cold car inside it takes forever to get the car itself warm.

Don't need to restate the posts above, but I also find the garage retains it's heat really well after opening the garage doors due to everything radiating. I can bring in a frozen objects and just lay them on the floor and they are thawed in no time. I also leave my temperature lower because it "feels" warmer at a lower air temps than forced air. I wouldn't hesitate to insulate, vapor barrier, and install pex in any future slab just so I had the option.

Good points but I'll stick to perimeter insulation and a mini split for heat. All the reasons I've read for why under slab heat is the way to go don't apply to my use. I am not a mechanic. There won't be vehicles brought in very often, if at all. I build teardrop campers. One per year, sometimes two if the stars align. The trailer may take me all winter to build. I buy the trailer chassis. I don't weld and at my age I won't start welding.

So I appreciate all the suggestions to go with some other method to heat the space. And I am genuinely impressed with people with mechanical skills like welding and designing. I work with wood and rigid foam. Woodworking is my passion, building campers is a compliment to that.

The purpose of these forums, as I see it, is to educate, debate and keep people from making huge, costly mistakes. So everyone, keep making suggestions. I'm not trying to stifle the discussion. But I have settled on a good plan for my purposes

 

[Wrench97]

To me it seems the difference lies in whether or not you intend to leave the system running all the time or not.
Around here I only run the heat in my garage(detached 25x30) when I'm out there my buddy with the in floor heat does the same so the slab is cold to start and takes awhile to warm up, I have forced air NG and not very good insulation so it gets warm but the floor lags behind I'm use to that since in the fleet shop there was always one door opening somewhere.....in fact in the safety lanes the doors were mostly left open all the time.

 

[4x4Pete]

A radiant tube heater in a insulated shop that is kept at a constant temperature will heat the entire space evenly just as well as infloor. I have no cold areas away from the heater. It cycles long enough to maintain temperature but isn't hot to stand under. My tools are all warm, the floor is warm too. Infloor radiant isn't anything special, except on GJ. I've been in 100's of shops with all styles of heat. Most were comfortable when the temperature was maintained. A properly insulated and sealed space has the biggest effect on how comfortable the space is.
I was at a job with one big shop (75x250), and they were installing lumber processing machinery. The installing contractor hit several loops when mounting the machines. That can't happen with radiant tubes, which is what they ended up installing after the infloor didn't work as well as desired. In and out with lifts of frozen lumber made it uncomfortable for the employees at workstations. The radiant tubes made all the difference. There's many anecdotal stories for and against various heating types. I honestly find the radiant tube, cheaper to buy, easier to install, out of the way, easy to service, and I don't have to worry about drilling into the floor. Oh, and if you did have the door open for a while, you can stand under it to keep warm. Try that with infloor.

 

[lovetap]

Good points but I'll stick to perimeter insulation and a mini split for heat. All the reasons I've read for why under slab heat is the way to go don't apply to my use. I am not a mechanic. There won't be vehicles brought in very often, if at all. I build teardrop campers. One per year, sometimes two if the stars align. The trailer may take me all winter to build. I buy the trailer chassis. I don't weld and at my age I won't start welding.

So I appreciate all the suggestions to go with some other method to heat the space. And I am genuinely impressed with people with mechanical skills like welding and designing. I work with wood and rigid foam. Woodworking is my passion, building campers is a compliment to that.

The purpose of these forums, as I see it, is to educate, debate and keep people from making huge, costly mistakes. So everyone, keep making suggestions. I'm not trying to stifle the discussion. But I have settled on a good plan for my purposes

I must have missed that. If I was intermittently heating the space I probably wouldn't go slab heat either. In my area where oil heat dominates i would throw a small furnace like a Toyo and maybe a small wood stove for wood scraps and call it a day.

Any way you go make it air tight and well insulated and anything will work.

 

[jblnut]

Yup.... floor heat systems are ill-suited to 'turn-down' thermostats.

Using in floor to heat the space the OP wants to heat it I’d agree 100%. I put a programmable thermostat in my shop (54x72x18) that turns the floor stat temp down 4f at 8pm. It turns it back up at 6:30am. I heat with a wood boiler and doing this allows the shop to cool off a bit over night and keeps the stove from getting hammered at night and gives me a longer time in between fills when it’s real cold. During the day I can feed the beast when I’m around and the slab can warm up again and become a giant thermal battery. I heat to a 66f floor temp and it is usually around 62f in the shop when it’s 15-20f outside. It’ll be 60f’ish when it’s -10f and 59f when it’s -25 and windy.

24x28 is a small enough space that it wouldn't be too much extra work to install pex at tight intervals like 6-9" which anecdotally seems to help with reaction time.

I spaced the outside 4’ of loops at 6” , then 8” for the rest. I can turn it up 10f at 8am and it’ll be there by 5-6pm. Can’t complain about that for recovery time in a big space with 6” of concrete. Running 95f water through it.