In floor heating vs. radiant vs. forced air in shop??

[Raspy]

Raspy do you install heating systems or just experienced?

I'm with you in that the cost to install during the construction phase is worth it.
I'm still working on the getting my 32x48 barn built, but it will have at a minimum a utility room with washer, dryer, shower and toilet. Nothing worse then sitting on the cold seat.

Most people suggest laying out the pex along the rebar. It seems to me that if you ziptie it to the rebar you should be able to locate the pex later by finding where the rebar is layed out.

Since I will putting walls in after the cement is poured it will be important to know the location of the pex.

Wedge

Yes, I do design and install them and have for 30 years.

If you put the tubing in a structural slab you certainly can tie it to the rebar as I mentioned in an earlier post. Easiest way is to use rebar ties and a tying tool. Decide in advance the tube spacing you want and run the bar on that schedule. Near doors run it closer with an extra bar or two. Generally, less bar is used without radiant heating if the bar will not be used to support the tubing. So if the plans call out #5 bar on 24 inch centers, you might go to #3 bar on 12 inch centers to accomodate the tubing and have similar strength and similar rebar cost.

Twelve inch spacing works well for general heating. But reduce it to six inches in bathrooms and near entry doors or shop doors.

The tubes don't need to be any closer that one foot from the exterior walls. They should not go under interior walls if you can help it, but instead go through doors to enter a room. Separate rooms should have separate loops so you can balance the flows to match the heat load in the various rooms. For instance, bathroom floors should be warmer than workout room floors. Kitchen floors run warmer than bedroom floors. This is done by regulating the various flows at the manifold. Separate thermostats control rooms with different purposes and different schedules. Such as the master bedroom and the dining room will have separate thermostats. But within each zone there can be many loops of tube if needed. For instance, a living room, dining room, entry and library could all be on the same t-stat located in the living room, but each room would have it's own loop of tube for balancing. This way you could lower the relative temp of the library while raising the relative temp of the entry, with an adjustment at the manifold, and all could run on the same t-stat.

If you know the rebar spacing, take some photos or just trace the temperature, you can find the lines easily later for drilling.

I'll include a few pictures. These show the manifold, the bathroom strategy for getting a lot of tube in with large radius bends and a general view of the layout. This happens to be a house done recently over an existing slab and using mesh to tie to. It has insulation, but I generally don't use it. In this case the general contractor wanted it.

 

[rswyan]

Patrick,

Thanks for the response.

With free gas to feed your in-slab and complementary heat source why mess with any heating method that wastes/takes up your time and is less eco-friendly?

Couple things:

1. I have free gas up to 240 mcf .... after that I pay normal rates (not wellhead prices) .... as long as that well is operational I don't ever wanna give the gas company another dime .... and actually, our allocation is currently set up for only 200 mcf (240 mcf is what the land man promised ... thankfully in writing, in an email) ... gotta call them and straighten that out ...

2. I have about 10 or 12 acres of immature woods on my property - the intent is to manage it for eventual logging of the timber. I could probably easily heat the polebarn during those times it is being used for a number of years, just from the wood I'd get from thinning and cleaning up snags and deadwood. So acquiring wood for fuel isn't really "a waste" of my time ...... it's serves a purpose ..... on the otherhand, I ain't getting any younger and am not looking to add unnecessary work to my life.

3. The waste oil is a freebie (my son has 10 vehicles, I have 3, not including equipment like the tractors) - I have to do nothing to acquire it, other than provide 55 gallon drums.

I'm curious about your thoughts on the eco-friendly aspect though ..... I certainly don't see heating with wood as being un-eco-friendly ..... it's a net carbon equation for the atmospheric envelope/environment - whereas any fossil fuel (ie. gas, oil, etc.) is not ....

Also, I don't think you really want to be in an enclosed space for very long with one of those torpedo heaters.

That's true - although I spent a good part of one winter working in my garage with it, and was surprised at how clean it was (relatively) ......

Of course, it took me awhile to realize what the CO was doing .... :confused2:

The torpedo heater was/is only an interim solution ... not a long-term one.

There are plenty of heaters that take gas but for your application I'd first consider overhead radiant. The kind I have in mind, installed, looks like a gas burner (big Bunsen burner looking thing with metering orifice and adjustable air inlet. Then there is a LOOOOONG exhaust pipe. The actual fire takes place in this pipe and the hot exhaust gasses heat the exhaust tubing which radiates heat into the conditioned space with the help of a linearized parabolic reflector mounted on top of the hot pipe to reflect heat down where yo want it.

Yup, I've seen 'em.

The heat is available only moments after lighting it off. Most of the heat is radiant, i.e. it heats you and other objects (and the floor too) rather than the air in the space. It almost instantly makes you comfortable as it raises the effective temperature of your radiant environment RIGHT NOW.

...... provided you are underneath or relatively near it ....I would guess ...

Keep in mind we are talking a 3000+ sq. ft. floorplan .... eventually there will be multiple work stations or work areas .... practically speaking, it's not likely that I will need to heat all of it, all the time, to the same extent ....

I sorta suspect that having enough of these placed in strategic places where work might occur could get kinda pricey .... as compared to a conventional forced air furnace.

They can easily be thermostatically controlled so no fussing like with several other alternatives.

I take it that the thermostat used to do so would have to be in the path of the radiation ? (since these type of heaters don't really warm the air all that much)

Is that how it works ?

Some of the direct heat does eventually warm some of the air in the space due to contact of the air with the hot pipe and a little convection takes that warm air up toward the ceiling but there is way less of this than many other heating methods.

I dunno .... the idea of not warming the air just doesn't seem terribly exciting to me for some reason .... might be my own "fixed think" in the area of heating cooling ....

Circulating fans are not required but do no harm if you want to try to get the hot air off the ceiling and down where you are.

A number of ceiling fans are part of the overall plan ..... along with at least one whole house/attic fan installed in the ceiling to provide cooling/air movement in the summer, and exhaust in winter and summer.

This would only be after the heat ran for a significant period of time not just an hour or so.

Right.

Even in-slab radiant eventually sends about 1/4 to 1/3 of its heat upward via convection so with both slab warming and additional "quick heat" you may want a way to circulate air to mix the ceiling heat in with the rest of the air in that space.

Yup.

There is nothing in a system with in-slab and another complementary heat source that precludes your also burning any of the other alternatives mentioned such as scrap and cord wood, corn, waste oil, old cooking oil, or whatever (except in my case laziness.)

Right .... (in mine too )

If had free gas to burn for the foreseeable future I'd go in-slab and overhead radiant, both gas fired.

Got it ..... I'll have to see how the building is in the summer and how cool it stays, once I get the ceiling and some insulation installed ......

Since the idea of going out there in the summer and ending up drenched in sweat while I'm working doesn't excite me all that much, I may end cooling some portion of it (think large curtains to partition off areas) .... so I may end up with ductwork anyways .....

(We also have a small concrete block shed (28' x 32') on the property that currently is my workshop ..... I put a small wall AC unit in that building .... was pretty funny ..... got a bunch of ribbing from a couple of local TBN friends about it ....)

Regarding insulation: The perimeter insulation gives more bang for the buck than under the middle of the slab so if you cut corners do it in the middle of the slab but insulate the heck out of the perimeter.

Yeah - I had read that somewhere (.... mebbe in this thread) ... figure I will go:

1. around 12" (vertically) of foamboard, 4" thick, up against the skirtboards (inside) on the building perimeter,

2. and then at least 2" of foamboard (horizontally) under the slab from outside wall 8' inward,

3. the rest of it (the interior rectangle) I will go 1" of foamboard ....

..... unless I can come up with a cheap source for foamboard ..... then I'll just do it all in 2" ..... and maybe stick 4" under the slab on the outer 4', next to the exterior walls.

Next question: Is it possible/practical/recommended to use poly-isocyanate foam board under the slab rather than extruded polystyrene (EPS) foamboard ?

(FREE GAS... so)

Yeah .... it's free ...... right now ..... but that can always change ...

The reason they put the well on my property is that a number of older wells (very nearby) had become inefficient in terms of flow (both in and out) - despite numerous attempts at frac'ing and getting them to flow more. These are storage wells that go into a large depleted reservoir that's being used to store natural gas.

I don't think they will be taking the well out of service anytime soon, having just drilled it .... but ya never know .... and the wells clearly do have a life (even if it is measured in tens of years ...)

You will create a heat bubble under the slab (unless you have a lot of ground water flow) and losses via that route will be much less than at the periphery.

Understand the "heat bubble" premise - but please clarify what you mean in terms of ground water flow.

The north and east sides of the building pad are cut into grade - the pad is about 4' to 5' below grade on those sides - and I'm guessing there probably is some flow through the ground. My "handle" for this is a combination of french drains (for "ground water") and hard drains (for gutters and surface runoff)

You need to insulate out beyond the foundation, stem wall, or thickened slab edges (however you do the mud work) to thermally isolate your slab from the cold shallow dirt in contact with the frigid winter air.

Right - see above.

There is a version of the wrapping material we all love to pop that has aluminized inner surfaces and is used under slabs for insulation. I have it under part of my house and under my shop slab. It works by reflection more than R-value and it is way cheaper than EPS. It reflects most of the heat back up toward the slab.

Yeah ..... I'm familiar with it ..... I have a cargo van which I insulated using 2" Dow EPS, 1" polyisocyanate, Great Stuff Expanding Foam ... the entire interior surface is covered in Reflectix bubble-wrap .....

I've also seen it used where it was glued directly to the interior sheetmetal in a van with no other insulation used ... and my impression was it was almost next to worthless ..... although maybe if used under a slab it would be the cat's meow .....

You aren't by chance familiar with this article written by John Siegenthaler are you ?:

Bad Science

If you sense we are getting too far off the thread theme of the OP, PM me for additional exchanges. Of course if the OP is interested, speak up and we can go on about it here.

Unless someone complains, I'll keep talkin' - I think this discussion may be of interest to others.

 

[wedge40]

Interesting post Raspy. I have questions about the photos. It looks like you have the walls in place before you pour the cement? Like they are on top of 2x4's and those will be the level point for the pour. Is that correct and doesn't this make it more work for the cement guys? If that what is happening?

Wedge

 

[Raspy]

wedge,

In this case, and it is done in a number of different ways, we already had a structural slab in the new house. Before the walls went up they put down pressure treated 2X4 plates to build on. Then the regular plates and the wall framing. We poured only 2 inches thick. The pour was Gypsum concrete. Done in ths way you just proceed as usual with the building and the lower plate disappears in the pour. Sometimes we just put the first pressure treated plate, then pour concrete and screed to the top of that plate, and then build from there. Gypsum requires a different strategy than concrete, but works well in interior spaces. It also gives a chance to cover conduits, low volt wires or water lines if needed, during the process.

I also pour 1 1/2 inches of concrete in this way over old slabs where we want to install a new radiant system in an older home. And on the second floor with conventional wood subfloors where we want to add radiant there.

The best way is probably to put the tubing in the structural slab and avoid the topping slab. These structural slabs are a minimum of 4" thick and I prefer 5 or 6 inches. Some have been as much as 24 inches. 12 is not uncommon. Mine will be between 6 and 8 inches in my new place.

Here are some pictures of my new framing.

 

[Raspy]

Here are a couple more pix of tubing going into a structural slab. This one has bar on 18" center and tubing on 12" center. I much prefer to have the tubing on the same schedule as the bar. You can also see the manifold, the ties and the conduit 90s.


John

 

[Raspy]

Here it is.

 

[magicheater]

I have in floor heat, I like in floor heat, it would be hard to have anything else.

 

[rswyan]

John,

I much prefer to have the tubing on the same schedule as the bar.

You mentioned this several times .... without saying why .....

Is it because you would prefer to run the tubing parallel to, and tied to the rebar - as opposed to just supporting the tube by crossing the 'bar perpendicularly ?

Less chance of damage by the concrete crew that way ?

 

[Raspy]

rswyan,

The main reason is to help prevent damage from he crew. The pix I posted, with the outside layout, have the bar at 18" and the tubing at 12". The guys will be stepping on and stretching the unsupported tubing.

When the tube spacing gets down to about 9" the guys can't avoid stepping on it because their shoes are longer than the tube spacing.

I've had very little trouble with tube damage during pours. It's important to lay it out carefully to avoid sharp edges, tying it to unsupported bar that might move and stress the tube, kinking it, tying return bends to avoid a snag pulling it up, etc. I use the rebar ties with the loops on the ends instead of the bailing wire method to reduce sharp points. This is part of the reason to use conduit 90s where it exits the slab.

 

[rswyan]

I found one guy in IL whose business is selling EPS cuts/drops (partial sheets) at a discount - but unfortunately I lost the address of his website.

Found it again - although it appears that what he is selling is not EPS, but poly-isocyanate foam board:

Insulation-Factory Seconds

Raspy - any comments on my question regarding the suitability of poly-isocyanate .... as opposed to extruded polystyrene ?

And thanks for the answers/clarifications on the layout/tiedowns.