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

[patrick_g]

In a non-commercial setting, say a shop used intermittently not all day, radiant floors are primarily a comfort issue NOT an economical solution. You can't use setback strategies due to the lengthy thermal time constants. You basically have to heat the floor/shop 24-7 because there is NO WAY you can get close to heating it on an impromptu basis. (turn heat on now with a cold floor and get to your room air set point temperature in a day or two or... I don't plan my shop use that far in advance.)

Irrespective of your heat production/application method depending on your infiltration and R-values there is a heating requirement for making up losses or you won't maintain your set point. Maintaining your set point 24-7 during significant cold spells when the shop is only occupied intermittently may not be the best application of your funds. I use my shop a lot, especially in winter and the hot-humid summer times but would rarely occupy it more than 1/3 of the time on a weekly average.

By all means do insulate the slab very well so that its temp will tend to be the average of the air temp in the shop which is way better than a really cold slab.

A more economical/efficient approach is to warm the slab sufficiently to achieve an acceptable level of floor temperature comfort but "finish" the job with another heat source (with a much shorter time constant.) This additional heat source can be radiant overhead heat, wood stove, forced air furnace, waste oil burner or whatever.

This gives you a workable compromise. The floors are not way too cold for comfort and your losses are greatly reduced. The additional heating method of radiant overhead, heated air, baseboard heat or whatever is employed with a setback strategy OR only used when you occupy the shop.

I am a great fan of radiant heating, especially in-slab but... it is a wasteful approach for a space that is only intermittently occupied and goes for several hours a day unoccupied. Now for residential heating... That is a different story with occupants randomly entering most spaces during about 2/3 of the hours of the day. You are more efficient.

If money, carbon footprint, and other ecological considerations are ignored then by all means in-slab radiant for the shop is a primo choice.

Pat

 

[Dog Lover]

Jer,
I recommend you look at this site: Radiantec Heating, Energy Efficient + Green. I put radiant floor heating in my ranch style home 6 years ago and have found it to be the best heat I have ever had. Consistent warm radiant heat with no drafts, no humidity issues and at a slightly lower cost than normal forced air heat.

Without a doubt investigate this site for all of your answers to your questions. It works and works well. Did the entire job my self and used Radiantec as my guide and source for all materials. I put in an Open Direct system that uneducated heating contractors said would not work. They simply did not know enough about it and were wrong. After completion they were simply amazed at how well it worked and one said he was going to do it in his home.

Can't go wrong with Radiant floor heating!

 

[patrick_g]

Can't go wrong with Radiant floor heating!

RIGHT ON! At least in residences or spaces occupied for a great enough percentage of the time to shift the economics solution toward radiant floors (in-slab) If your floor is NOT CONCRETE then radiant floors can be economical alternative to other heat even in spaces only intermittently occupied. My master bed room has a radiant ceiling (really thick pad and carpet nixed in-slab heat from geothermal heat pump.)

In this bedroom you can do temp changes (or employ a set back strategy) because the only thing between the PEX carrying hot water and you is sheetrock which has a low R-value and low thermal inertia (low heat storage characteristic) so the temp can be yanked around fairly well (unlike with in-slab.)

No arguing the comfort issues. I like to go barefoot at home and we have lots of porcelain tile floors which with other than in-floor heat would be uncomfortable.

Although in-slab is ductless with its inherent advantages, if you want to cool the space it is likely you will end up with ducts anyway (in a larger application.) In the shop application, depending on size and interior layout/walls you might do well with one or more window units (can be installed in the wall.) A couple window units instead of one big one can be a better deal. The higher percent of the time the A/C is running the better it dehumidifies. Also the efficiency of a freon/compressor system goes up with runtime pretty much getting to its best performance in say 40 min or thereabouts. So having one little A/C unit run continuously in hot weather and the other cycling as needed is not a bad solution. For larger installations look for a variable or multi-speed compressor NOT just a multi-speed fan/air handler or one of the units with two compressors in the one enclosure.

Radiant cooling is an alternative but the engineering is even more out of reach for most vendors/installers of HVAC than with radiant heating. HINT: You definitely do NOT cool the floors

READERS DIGEST VERSION: Using only in-slab radiant good for house but NOT so good for shop unless being green, carbon footprint, higher installation/operating costs, and such are not a concern.

Pat

P.S. A side note: Most HVAC vendor/installers are not capable of properly engineering and installing a conventional HVAC system let alone radiant (hydronic or otherwise.) DOE stats show 75% of HVAC installs have oversized units. Why? A few reasons... If you can't figure out how much is enough then go bigger and cover it. The system will cool and you won't get call backs for it not cooling enough. Also there is more profit in larger units. Unfortunately larger units short cycle (spending too much time on low end of the efficiency curve so operating costs are higher, dehumidify poorly, and wear out sooner. All good things for the seller.

 

[rswyan]

I have a 42' x 72' x 12' polebarn we put up about 5 years ago .... we are shooting to get at least a portion (1/3 to 1/2) of the floor poured this year before the snow flies .....

I think we are going to go with a hybrid/dual system - radiant heat in the floor to maintain the building above freezing and take the chill out of the floor - and something else to rapidly heat the air in the building - could be woodstove, gas forced-air, waste oil, whatever .... maybe a combination of all three, since I have access to all fuel sources. I have a 175K BTU torpedo heater, so that's probably what we will use initially.

We are lucky in that the gas company approached us last year about drilling a storage well on our property - so we have free gas - up to 240 mcf per year (the house uses about 110 mcf per year)

The walls in the polebarn are already very well insulated (5.5" of sprayed cellulose), I just need to get the ceiling installed (already have the steel) and get some insulation in the attic - along with coming up with the insulation for below the slab.

For us that is the toughest one, due to the expense .... buying 2" EPS at Lowes or Home Depot ain't gonna cut it. 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.

If anyone has a source for cheap EPS insulation please feel free to chime in - location may not be an issue as I drive a large (about 500 cu ft) cargo van over-the-road for a living, and could easily swing by somewhere when I'm deadheading home.

BTW, I own a two story commercial building (built around 1958) that we lease out to a tenant, which has radiant in-floor heat on the first floor (copper tube) and baseboard radiators on the second. It was formerly the location of our family business - and the employees always enjoyed having warm feet in the winter. The building is heated by two hot water boilers - we just replaced the boiler for the first floor this past year - IIRC, the cost was just over $3800 (installed) - but the boiler was over 30 years old :thumbsup: ...... and may well have lasted even longer had it been maintained better.

 

[patrick_g]

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

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. 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.

They can easily be thermostatically controlled so no fussing like with several other alternatives. 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. Circulating fans are not required but do no harm if yo want to try to get the hot air off the ceiling and down where you are. This would only be after the heat ran for a significant period of time not just an hour or so.

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.

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.)

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

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. (FREE GAS... so) 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. 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.

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.

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.

Pat

 

[Raspy]

Radiant in floor heating is by far the most comfortable of all systems. Unfortunately, not very many people know a lot about it and too many perpetuate all the myths. Such as:

You can't use setback thermostats. Wrong. I use them on all of my systems with excellent results.

It takes way to long to heat up so you have to leave it on all the time. Wrong. It does take longer to heat an area than with forced air, but there is no way anyone would leave it on all the time, or need to.

You'll need another system to get the room up to temp fast while waiting for the radiant. Wrong. Nobody with a good radiant system uses anything other than the radiant, even if they have it waiting to go. Over and over I'm told their favorite thing about the house is the radiant. Anything that blows heat around also makes noise, stirs dust and sends all household cooking and other odors throughout the house. People with severe allergies insist on radiant.

Cold floors "radiate" cold into a room. Wrong. Cold surfaces absorb heat. Hot radiates toward cold. People feel warm in radiant heated houses because they are absorbing radiated heat from the floor, or are at least not radiating very much of their own heat toward the cold surfaces. Eventually, this radiated energy warms the entire room with help from convection currents. A cool room feels warm if the floor is warm. This is why the response time can be shorter than expected.

A good radiant floor in a home will only be running at about 75- 85 degrees to make it completely comfortable. This heat can come from a water heater, a boiler, electric resistance wires (not the best choice and only viable for very small areas), a wood burning boiler, solar thermal panels or anything that will make water warm. A good rule of thumb for the amount of heat needed is 25 BTUs per square foot. 10 will barely work. 50 is good for larger single thermostat systems with close tube spacing or very bad heat loss. 25 is fine. A modern home has a heat loss of about 7 BTU/sq foot.

My new home will have about 2800 sq ft of heated space including the shop/garage. It will have 4 thermostats. I'm at 4900 feet elevation. I'll probably be dedicating about 70- 100,000 btus of the boiler's available output to it. The boiler will be a backup to the solar that will use the slab and water for storage. I'll most likely not use the boiler very much, but the solar will be sensibly sized to keep it out of trouble in the hot summer.

Oxygen barrier PEX tubing is the best on the market for radiant heating. In a structural slab poured on the ground, this normally would be arrainged in a serpentine fashion, tied to rebar and spaced 9-12 inches apart depending on the severity of the location, the response time needed and the temperature of the delivered water.

With 1/2 inch tubing (5/8 inch OD) the maximum length for each loop would be 300 linear feet. So, a garage for instance, with about 400 square feet and tubing spaced about 12 inches might be two loops. More if you run extra in front of the doors or want to divide off a bathroom with it's own loop. I always run an extra loop or two near the doors at 6" and closer spacing in the bathrooms at about 6". All tube ends come up out of the slab through 3/4 inch PVC conduit 90s and sweep up to a manifold that connects them and ties them into the supply and return piping from the heat source. Set up the rebar spacing on the tube spacing you choose for best esults. Not necessary, but better.

On raised wooden subfloors the tubing is stapled down directly to the floor and poured over with a thin slab, often 1 1/2 inch. On existing slabs, 6-6-10 mess is shot down and the tubing is tied to it with 6 inch rebar ties before a topping slab is poured over. Normally 2 to 4 inches thick.

The heating system will always be closed loop. This means a dedicated heat exchanger, boiler, water heater or other unit just for the radiant.

Controls can be as simple as a thermostat turning on a pump or as complicated as individual loop controls and many thermostats throughout the house.

Even if you are not sure how you might make it all work, it's a good idea to get the tubing into the pour and be ready. You can do this yourself. Get the tubing in and connected to the manifold. Install a gauge and get some pressure on it. Pour. It's unlikely you'll damage the tubing, but if you do, just fix it and keep going. Use brass barbed inserts with copper crimp rings to make repairs that will not fail. I always leave a repair "kit" at the job sites for the concrete guys, but it rarely gets used.

Any particular questions I can help with?

 

[crazyal]

If given the choice I would add it. If it's a part time use shop I would really want it. Forced air does a losy job at heating up a cement slab. Heat rises so getting it to warm the slab up is hard. Add things like equipment blocking direct flow just makes it that much worse. Just heating the air up inside the shop but standing on an ice cold slab isn't fun.

Downside is of course you can't just drill holes in the cement unless you know where your lines are. I've heard of people spraying water on the floor then turning on the heat and looking for signs of the pipe or using an indirect thermo prob to find the hotter spots as an indication that it's close to a pipe but I've never tried it with mine.

 

[1950T]

my shop is heated by 2 woodstoves and ive got celing fans that push the heat back down. truthfully ive only ever ran one. with the wood stove and the coke forge going my 20x35 shop stays toasty.

 

[wedge40]

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

 

[Conservation]

I missed the part about free gas. If the gas is free, go in-floor for sure. Very comfortable. If the gas is not free, hang a gas radient or conventional. Set back and save money. I saw the part about set backs being ok, but I have not seen one like that yet.