In-Floor Heating for a Shop & Greenhouse - Considerations ?

[Rustyiron]

Scotty I'd argue that radiant excels in a shop with the 50+/- ton warm flywheel (slab).
Opening a garage door even at a nascar pace with a ceiling hung air heater pretty much flushed out your heat and your starting from 0 with every door opening cycle. Then there's the 5 tons of cold steel you just rolled sitting there in your building. brrr
This is one of the first things I realized with my radiant shop as I've had the "air heat" in 2 prior shops.

 

[cj7]

I had it in a 32x40 pole building in western PA. What I learned.

My builder did not insulate my slab well enough. Should have used something better than the double bubble wrap. Also should have insulated the perimeter 2 to 3 feet down with 2 inch foam board.
Inside a ceiling should have been installed and insulated to R39. Walls needed more insulation as well. The insulation was the double bubble wrap.
I had 18ft long doors on each gable end. This made for 36ft of concrete that would wick the heat from the slab. The doors never froze but its an area to con sider a better solution.

Performance. I loved the heated floor. As others have stated it was slow to bring up to temp. Recovered much faster after having a door opened.

I had either a portable propane or wood burner to ue for faster heat and help when the temps were down below 20.
Since the building sat on a hill and would get plenty of wind in the winter the system could not keep up once down in the low 20's. I had to use another heating source. The boiler alone could not keep it at 40.

I did not use the floor heat often as the boiler was electric. I was never able to add insulation to make the electric bill less.

 

[rScotty]

Scotty I'd argue that radiant excels in a shop with the 50+/- ton warm flywheel (slab).
Opening a garage door even at a nascar pace with a ceiling hung air heater pretty much flushed out your heat and your starting from 0 with every door opening cycle. Then there's the 5 tons of cold steel you just rolled sitting there in your building. brrr
This is one of the first things I realized with my radiant shop as I've had the "air heat" in 2 prior shops.

Sounds to me like we are saying the same thing?
rScotty

 

[Rustyiron]

It is best used for maintaining a baseline temperature - that is its strength & makes it great for houses but less so for a shop.

This is what confused me.
I must have misunderstood something

 

[Menagerie-Manor]

My 30 x 50 shop is piped for in-floor but as others have mentioned the warm up can take forever, using a programed T stat is an option but fuel costs really impact that. I added a ceiling hung HW unit heater to the system for initial warmup and also added a wood stove. If I'm in working regularly on a daily project then I'll maintain like 60 deg on the radiant, otherwise the other options.

 

[dstig1]

I hear this regularly about radiant floors taking "forever" to warm up. You see my shop up above in an earlier post. If I start up the radiant for the year while it is in the mid-upper 50's in the shop (about the point I can't stand being cold anymore) and keep working, it cycles off in an hour or two. Now it starts back up again and cycles a bit more frequently for a while until everything saturates but the shop is basically up to temp in that time. This is not "forever" by any stretch. The very first time I started it up, I left it overnight hoping that it would be warm in the morning since it takes "forever" or so everyone said. It was fully heated up and cycled off when I came back in. I keep it around 68 in there. Since then I have been working in the shop when I first turn it on, so I know it runs solid for an hour or two and then starts to cycle. Not forever...

But again: R10 below the slab and at the edges. R22 SIPs wall, and R40ish blown in ceiling. Garage doors are high quality R17 ones. Good insulation helps a ton. No sense heating the outside... But sure, if you have an uninsulated pole barn, then good luck. I'm sure it WILL take forever if it ever makes it at all...

I still haven't started it up yet this year. Temp is hanging around 60-61 inside now. Hoping to hold out until Nov, but all depends on the weather...

 

[PandDLong]

A lot of excellent advice and considerations - much appreciated!

Insulation - plan to take full advantage of the wall cavity to get R22 as a minimum (may be able to push it to R29), ceiling will be R50, under-slab is R15. Garage door is only R12.

Currently there is no plan for perimeter in-ground insulation and many comments are "do it".

How do you "top" the vertical form board around the perimeter?


I may defer adding the boiler until I am working less and have more time to enjoy a warm shop and keep it heated. Although I have to consider the comments that once heated, it is cost effective to keep it somewhat warm. I will also look into some of the creative lower-cost boiler alternatives that some of you have successfully put into place.

For now the focus is making it radiant-heat ready - so the insulating and pipe install.

Michael

 

[PandDLong]

There is alot of science and design in making loops efficient.

Not much different than duct work sizing in a house. Sure....you could throw together duct work and blow the conditioned air through the house.....and it will work. But a proper system is designed for balance and efficiency.

The perimeter of the slab needs the loops closer together than the middle. Otherwise the perimeter of the slab will be colder and the middle will be warmer.

You need to pay attention to which is supply and return. Sending a loop supply down one wall.....return it down the same wall. Not just make a circle around the building. Cause if you do that for a few consecutive loops.....you basically have all your supply (hot) loops all next to each other and all the return (cold) loops next to eachother. MAkes for uneven heating.

And yes....it is a very SLOW temp change with radiant. Dont expect to go out there when its 40 and jack the thermostat and have it 70 by lunch time. Radiant shines for a constant, even, and quiet heat. Which is why I heat my shop with wood. Quick warmup if Im down there, and cost nothing if im not.

Also....the perimeter of the slab needs insulated as well. Many people overlook this and only insulateunder the slab. But most good installs will dig a trench along your band-board/skirt board.....and install a vertical 2" foam board going down into the ground about a foot below slab level. Prevents cold creep from coming in under the slab.

Also gotta watch freeze if you install loops but then choose not to heat a certain area.

Doing radiant heat the right way is definitely not something to just DIY-wing it. You need to know and understand exactly what you are doing because there is no way to correct it in the future

Great tips on setup. And identifies it makes sense to get an expert providing some on-site advice.

Is the vertical 2" foam board just covered with dirt or ...?

Michael

 

[LD1]

The vertical foam board isn't there so much to insulate the slab edge from the band board. It's there to insulate the ground under the slab from cold/frost creeping under the slab, lessening the burden on your below slab insulation.

Some people run the edge foam all the way to top of slab. I personally don't like that...rodents can tunnel through that foam and have easy access to wall cavity.

Leave foam board 1"-2" below top of slap. Let concrete cap it

 

[5030]

That's a good point - i have heard that once it is warm, keeping it a low temperature takes little energy. So it may be less energy to heat and keep at a low temp than cycling hot/cold. May take a bit of experimentation to find the right balance.

That is correct. If you live in the north (like I do) and have in floor heat like I do in my shop. Once it's up to temperature (in my case 70 degree slab temperature), I maintain that all winter whether I'm in there or not because it requires an inordinate amount of fuel (in my case propane) to heat the slab back up. Much more efficient (fuel usage) to maintain the slab temperature constantly (my slab is quite thick because it carries heavy machine tools.

I've had about 10 years to experiment with different scenarios and I've come to conclusive results and that is I leave the in floor PEX on all winter at 70 degrees slab temperature and I monitor the slab temperature with a remote sensing t'stat inserted in the heated slab itself an encapsulated in epoxy.

My ambient air temperature is usually 10 degrees less than the slab temperature btw.