Hot Rod Forum banner

Radiant floor question

10K views 29 replies 13 participants last post by  ArronEhrhart 
#1 ·
I'm getting ready to install the foundation and slab for my new shop, approx 50 ft by 60 ft. I was planning on putting PEX for radiant heat in the slab, but I'm having second thoughts for two reasons and I'd appreciate comments from those with experience. I'm located in the Washington DC area, so it gets below freezing for about two months over the winter.

First, I plan to install A/C as well - summer in DC is a swamp. Since I have to run ducts and an air handler anyway, would it be better to just use forced-air heat, possibly with a large outdoor wood-burning furnace?

Second, every radiant floor design guide I read cautions about furniture blocking the heat from the slab. Since my shop will have a number of cars parked in it, in addition to equipment in a machine shop and several pallet racks for storage, will the heat from the slab be blocked anyway?

Of course, I'm also worried about puncturing the tubing when installing things like a lift... :eek:

Thanks for your inputs.
 
#2 ·
joe how are you doing? i live in Arlington and two yrs ago built a 24x23 garage with Pex tubing in the floor for the radiant heat.....i have never hooked it up. my garage is 2x6 construction with 14' cielings roof trusses and well insulated . 3 windows, side door and large 18x8 garage door. the reason i never hooked up the pex was that i had an electric dayton 240v heater and for the time i use the garage weekends and nights i just turn the heat on and it warms it up to any temperature i want mostly 63-65*. it costs me about $1 a day to heat it. so with the high initial cost of the outlay for the radiant floor heating manifold etc i just cant bring my self to ante up the $$$ to pay for it. i had no problem laying the tubing and i knew before hand where the lift would go and at the same time i added more rebar to that area i moved the pex tubing away from it. i see no reason why you cant have more or less tubing in certain areas then others. for me while it would be nice to have i just dont see the cost justification for doing it at this point. running the tubing is the least expensive part of the project and is what i did so i have the abiltiy to add the heating source and manifold later if and when my current heating sources breaks.

there is no reason not to have a combination of two systems......forced hot air for overall shop and then the area where you have the machine shop or lift for working on cars have the radiant floor heating there.

you will want to insulate the under side of the slab so you have thermal break between the ground and what the slab you are heating.
 
#3 ·
HVAC is one area that I am confident in..Given what you have described I would go with a roof mount system with the ducts in the ceiling as this is the most practical for a commercial type building..Of course you can use an updraft furnace to feed one of those systems if you cannot do a roof mount. When one does the heat loss one finds the A/C is the energy sucker and the heating load not so much..To keep heating/cooling costs down we cool to 75 in the summer and heat to about 55/60 in the winter..this seems to work out fine for a working shop..The wood burner may be a problem as I am not aware of any A/C units that use wood for the heat side.

Sam
 
#4 ·
week end work ?

with radiant it takes a while to get the slab warm. IF you want it to stay warm all the time.they work good. . In the 4 car house garage we have a gas forced air system, just crank up the thermostat when I want to work. back down to 50 when just parking the cars inside.
 
#5 ·
joe
if your installing AC then i would stay with forced air heat.
no sense installing 2 systems. $$$ mega bucks $$$

frame it and insulate it like you would a house.
a pole barn is tricky to insulate well.

also think about partitioning your shop into heated and unheated sides.
my shop is 50x50, i have a 20x30 always heated work room,
a 17x30 heat as needed car bay and the rest is unheated.


all these doors go into a 20x50 unheated space.
there is a second door throgh the 16 ft door into the heat as need space.

 
#6 ·
I'll reply to Q2 only as the economics are for you to decide.

Measure and figure out where your lift anchoring bolts would go and avoid running tubing there. If you can't or won't then if you wet the floor and turn the heat on you can determine where the tubing is fairly easily. A parked car will not block the heat, having insulation and vapour barrier under the slab will greatly "encourage" the heat to travel up to heat the room. In my opinion the heat from radiant is nicer, especially in a high ceiling garage as it heats the area where you are (the lowest 7 ft) and when you are creeping around on the floor if its a while before you get a hoist. Watch out for unintended naps under the vehicles ;)

Have to agree with other posters, slab heating slow/gradual/continuous, not good for fast turn on, a timered/setback thermostat deals with that.
 
#7 ·
Floor heat

joe_padavano said:
I'm getting ready to install the foundation and slab for my new shop, approx 50 ft by 60 ft. I was planning on putting PEX for radiant heat in the slab, but I'm having second thoughts for two reasons and I'd appreciate comments from those with experience. I'm located in the Washington DC area, so it gets below freezing for about two months over the winter.

First, I plan to install A/C as well - summer in DC is a swamp. Since I have to run ducts and an air handler anyway, would it be better to just use forced-air heat, possibly with a large outdoor wood-burning furnace?

Second, every radiant floor design guide I read cautions about furniture blocking the heat from the slab. Since my shop will have a number of cars parked in it, in addition to equipment in a machine shop and several pallet racks for storage, will the heat from the slab be blocked anyway?

Of course, I'm also worried about puncturing the tubing when installing things like a lift... :eek:

Thanks for your inputs.
I have in floor heat in my shop and house, It is great and my shop costs less than the house.
Onemoretime said put it in the roof, bad idea, heat goes up, cold comes down, the higher up your heat, the higher the space is on the floor that's cold. With in floor heat your warm from toe to head.
The fluid in my lines are heated to 120 degrees so that goes through the lines the floor will be about 79*, it's all in what you set your stat to. I have two big fans, 3 blade that I have turning very slow pushing the air around .
My shop is 30' X 60', half has a 15' ceiling the other half has a 10' foot ceiling. When I built it They put a extra 1" of sand down, then 2" of foam Then the tubes 2 zones, then cement which they put a extra 1" of, so I have 5" instead of 4"
When it was down around zero I turned my heat down 20* from 70 to 50, the 1st week it was anywhere from -5 to -28 degrees, outside. The temp had only dropped 9* degrees in that week, after two weeks it had dropped 17* degrees, but the temp was a little above zero during the day and below at night.
I didn't put in central air I got the two biggest 110v a/c that I could get brand new about $275.00 each at the end of the season when they wanted to get rid of them. Central air would have been close to $2000.00, not counting duct work, I run both until cool, then shut one down, they are way up high and run by a hand held control, both on the high end of the shop.
I have only 3 windows and the service door plus big doors. This winter we have had a lot of snow, I watch by the big doors to see if the snow melts from leaking air it doesn't.
I have a lift but I don't have it bolted down as it has wheels and I can move it around. There is a upstairs, It is not heated but the heat goes up there and keeps it warm.
I live in MN so we get cold weather, the only thing I worry about is falling asleep on the creeper because it is nice and warm down there. :mwink: :D :thumbup:

Bob

Oh you can run it with wood from outside or pellets, corn, gas, which ever way you want. You don't have the cost of duct, and you can break it into zones, so you only heat what you want. :thumbup:
 

Attachments

#10 · (Edited)
I have the PEC tubing in the floor of my shop and would not trade it for any thing. Little further south than you, but in the mountains so don't think our winter temps are that far apart. I lived in Utah for 6 years with infloor heat and it was the best heating system I ever had. Two oversized 2 car garages with infloor heat and stayed at 50* all winter long. The primary heat source for the water was solar, with a tiny Paloma natural gas heater as a back up. The solar panels worked every day, regardless of the cloud or snow cover. Saw some temps down to -34F and the inside temp never varied more than 1/2 *. My shop has a 22' apex and it is chilly up there, but comfortable on the shop floor. The thermostat is set for 50* and holds well except if a roll up door is open for more than a few minutes. The thing about radiant heat, all of the vehicles, tool boxes, benches etc absorb the radiant heat and act like a reservoir of heat. They and furniture are a plus, not a negative. I use propane to heat the circilating water and have a 100 gal tank. This winter, I will use less than 350 gallons and the heat has been on since the first of Nov and will probably go off in mid to late March. This year, we will add hot water solar panels to the roof and the propane will become the back up.

As mentioned earlier, if you pour a 5 inch floor, then you will not have to worry about putting your lag bolts in if the PEC is installed 2" above the foam insulation and you don't try to drill your holes more than 2.5". Two inches is plenty for a 4 post lift, using epoxy to anchor them in. If you are going to install a 2 point, you might consider enlarging the foot print and adding more anchors. Do a search on my thread, Designing a New Work Shop and there are a lot of pictures and verbage on how it was constructed.

Trees
 
#11 ·
I appreciate all the good comments, thanks. I suspect that I'll stay with the PEX. I do plan to have walls inside and heat zones, so the storage areas don't need to be as warm as the work areas. I also have a couple of roof-mount solar hot water panels and was planning on plumbing those as well - every little bit helps and they're already paid for.
 
#12 ·
I have heard some horror stories from some of the HVAC guys here in Northeast Pa about the concrete not being so friendly to the pex tubing.
It doent like the expansion / contraction thing as well as the chemicals from the concrete while curing.If it springs a leak for whatever reason ,you cant fix it.
Honestly If it were me, I would put in radiant baseboard around the perimiter of the shop, use an outdoor boiler and an oil fired one for backup with a heat exchanger. There are outdoor woodstoves that can be multifueled, but I have checked into that for my remod, and they arent as efficient as putting in a dedicated unit.
With radiant it feels warm all the time and it is very even heat. Fanforced only feels warm when it is running, it stirs up a buttload of dust and its impossible to put the "unit" outdoors to contain the burner away from the air in the shop(VOC , solvents thinners etc. explosion...you get it)
I like the outdoor woodburner my neighbor has, itkeeps his house at 80 degrees inside all winter long.
I have an oil fired burner and my house is small and tight, I have used 275 gallons of oil so far this winter.
If oil keeps going up, I will be getting an outdoor stove and putting in a heat exchange for the hydronic (radiant baseboard) system in my house. If the fire goes down at night the oil fired boiler will pickup the slack.
Linn A
 
#13 ·
Also , instead of using zone valves , I used the TACO 007 series pumps with the integral check valve. They work great for zoning, and it is cheaper as you dont need the valve and a pump. just a pump.Pretty easy to wire up too.
 
#14 ·
Copper coils are the best but were out of my budget. Did quite a bit of research on the web and decided that PEC is second best choice. The "experts" claim it has better flexibility for the expansion/contraction of the concrete than the copper, but the copper does have the best heat conductivity. You are going to have zones, whether you want them or not because you want to return the water to the boiler/heat exchanger with some heat still in it. The TEMP Delta does not need to be too wide, or it takes too many BTUs to get it reheated for circulation. In the larger section of my shop, I have three closed loops feeding from one manifold and the smaller section has the same. One thermostat in each section controls the pumps and these thermostats are located about the center of an interior wall. The pumps are 24 volt DC TACOs that have been used in industries for a long time and have a good track record.

Convection heat rises and it is very warm next to the ceiling when it is used. This is really wasted heat unless you want to install a system to return it into the ducts. Radiant heat does have some raising but tends to warm objects. The warm floor means warm feet and very comfortable on a creeper so the thermostat can stay low and still be comfortable. My office/bathroom is located 11 ft up and is not heated. It is about 7-8* cooler than the floor level. We have a small electric heater if we are going to be in the office any length of time and because the office is also insulated inside the insulated shop, it warms up quite rapidly. Of course, you don't linger on the throne if you had not planned your daily constitutional. This spring, we will install a Mitsubishi ductless heat pump in it that will cover our needs

Trees
 
#15 ·
to bring the heat down from my 14' cieling area where the electric heater hot air finally winds up i use a slow turning cieling fan that is switched with my lights and an 8" round duct that goes from cieling height to floor with a fan motor in it that is on a timer and every 15min of every hour it circulates the hot air back down to the ground level. this creates a 1* difference in temperature from the cieling area to the ground area. i even use the fan in the round duct when i dont have the heat on and it moves the warm air from the solar radiation back down.. my son actually declared that 8" round duct with the fan in it as one of my best ideas.
 
#18 ·
radiant floor heat.

ogre said:
i do like teraplane's system. if you need air use the window units and then go with radiant floors.
my shop was retrofitted from an old barn

teraplane: nice freaking shop :thumbup: :thumbup:
Thank you, Since it was built I have had to add to it. In the picture behind my boat, and bathroom, I have added a 12' X 16' kick out for some more room, no heat in floor there but don't need it as it is not a work space.
Also wanted to make sure my shop had more sq. feet than the house, just to needle the wife a little. :evil: :rolleyes: :mwink: :thumbup:

Bob
 
#19 ·
latech said:
I have heard some horror stories from some of the HVAC guys here in Northeast Pa about the concrete not being so friendly to the pex tubing.
It doent like the expansion / contraction thing as well as the chemicals from the concrete while curing.If it springs a leak for whatever reason ,you cant fix it.
Honestly If it were me, I would put in radiant baseboard around the perimiter of the shop, use an outdoor boiler and an oil fired one for backup with a heat exchanger. There are outdoor woodstoves that can be multifueled, but I have checked into that for my remod, and they arent as efficient as putting in a dedicated unit.
With radiant it feels warm all the time and it is very even heat. Fanforced only feels warm when it is running, it stirs up a buttload of dust and its impossible to put the "unit" outdoors to contain the burner away from the air in the shop(VOC , solvents thinners etc. explosion...you get it)
I like the outdoor woodburner my neighbor has, itkeeps his house at 80 degrees inside all winter long.
I have an oil fired burner and my house is small and tight, I have used 275 gallons of oil so far this winter.
If oil keeps going up, I will be getting an outdoor stove and putting in a heat exchange for the hydronic (radiant baseboard) system in my house. If the fire goes down at night the oil fired boiler will pickup the slack.
Linn A
latech said:
I have heard some horror stories from some of the HVAC guys here in Northeast Pa about the concrete not being so friendly to the pex tubing.
It doent like the expansion / contraction thing as well as the chemicals from the concrete while curing.If it springs a leak for whatever reason ,you cant fix it.
That is just plain bs , Expansion and contraction? how much do they think that concrete slab grows and shrinks? PEX tubing has a 100% minimum expansion rate. How do you think it survives having the end expanded to insert a fitting , such as the Wirsbo PEX system uses? PEX tubing is not affected by concrete, it is designed to be used in concrete. Your source must be referring to someone who used some other type of tubing. Can't fix a leak? Yes it is a bit difficult to fix the leak, you need to chip the concrete away from the tubing to put a repair coupling in it, but unless you drill a hole in it there won't be a leak. A continious loop of PEX poured into concrete is virtually impervious to damage
 
#21 · (Edited)
pex radiant.

All splices- joints must be out of the concrete. continuous run under the concrete. as far as expansion contraction, I have seen concrete roads buckle in the hot sun . That should not be a problem inside a building out of direct sun. if you build over expansive clay soils you can have floor cracking. In a lot of areas the local building department already has area soil maps. I hit clay down at 4 ft. My engineer spec'd 3 ft sq footings with 12 in sq posts with 6 pieces of 1/2 rebar uprights with 3/8 hula hoops 6 in apart for the steel column supports. There has been no movement in the 20 post locations. The footings must be deep enough for the soil type or a grade post-beam system. 18 inch holes about 6 ft deep with rebar L'ed into the floor, and foundation walls about a foot thick floor around the edges and use lots of rebar in the floor slab. Plenty of crushed rock then poly vapor barrier, sand and foam insulation. Grade the area around the building to keep rain and snow melt water away. In my main 12 X 12 doorway I also brought out 1/2 rebar 18 inches apart to tie into the driveway slab The backhoe weighs about 10 tons. . In 9 years there has been no movement or cracking in the main doorway. . In the back door the slab has lifted about 1/2 inch, I didn't put in the rebar ties out like the front and the ground base level is 18 inches higher, not as good of drainage. I had about 100 yards of base gravel hauled for under the floor, I should have raised it more, but didn't like having to do a 3 ft in 40 ft ramp in front.
 
#22 ·
A qualified in floor heat guy will pressurize the loops for about 48 hours before the pour and leave it on until ready to hook up the system to the manifolds. Having pictures of the loops before the pour helps to ease you mind when core drilling for anchor bolts later.

Trees
 
#23 ·
radiant floor heat

trees said:
A qualified in floor heat guy will pressurize the loops for about 48 hours before the pour and leave it on until ready to hook up the system to the manifolds. Having pictures of the loops before the pour helps to ease you mind when core drilling for anchor bolts later.

Trees
They never put any pressure on mine, but it was two big loops, one for each zone.
My house is the same I have five zones and they are each one loop no splices or breaks in tube from start to finish, And they run pretty close, when I say loop I might be using the wrong term, as the tube went back and forth across the room or zone, not a big circle.
It's just like wiring a car less breaks in a wire less trouble.
So one end was hooked up to the out manifold, the other to the return, there were no breaks in between.

Bob
 
#24 ·
Old Fool said:
That is just plain bs , Expansion and contraction? how much do they think that concrete slab grows and shrinks? PEX tubing has a 100% minimum expansion rate. How do you think it survives having the end expanded to insert a fitting , such as the Wirsbo PEX system uses? PEX tubing is not affected by concrete, it is designed to be used in concrete. Your source must be referring to someone who used some other type of tubing. Can't fix a leak? Yes it is a bit difficult to fix the leak, you need to chip the concrete away from the tubing to put a repair coupling in it, but unless you drill a hole in it there won't be a leak. A continious loop of PEX poured into concrete is virtually impervious to damage
ALLRIGHTY THEN. Now that we have cleared that up.Sure am glad i didnt use that guy for my house.
I was questioning the info I got .I personally dont like pex anyway, too newfangled.
I do understand what you are saying about the expansion and contraction of the tubing and the concrete.
Like I said , what I have heard were horror stories, as far as I am concerned the jury is still out. Call me stupid if you like, I just dont jump on every NEW thing as the BEST thing.
I see alot of posts that guys put up saying it is the way to go,must be something I am missing. I am kinda hardheaded :)
 
#25 · (Edited)
When I built my garage, I was pretty hyped about in-floor heating.
Yes a warm floor would be a godsend if you spend a lot of time lying or kneeling on it.
The downside is that recovery times from opening a door would be considerable, and might even require a forced-air unit to re-heat the air.

After studying all of that, and weighing the costs and risks involved ... I was persuaded by a few friends to simply install a radiant-tube heater, along with a couple of industrial-type ceiling fans.


The radiant heat warms ME more than the air, but it also warms things like windshields and car bodies ... which in turn help to warm the air. My garage is well-built with 6" walls, vapor barrier, and R20 insulation.

The ceiling fans help to circulate the air under the vehicles and to warm the floor to a relitively comfortable temp. They also keep the windows clear.

In summer, the air movement over the cool engineered concrete slab helps to keep the garage at a fairly consistent and comfortable 20°C (70°F) temperature even during the hottest of days we get here.

It was relatively cheap to purchase and easy to install, and very economical to run as well. I heat my garage continuously as I have pets that live out there, but friends run theirs only when they plan to use their garage. It only takes about 1/2 hour before it gets comfortable enough to be out there.
 
#26 ·
Bob, I use the term "loop" because the line /water leaves the manifold and makes its way through the coils and back to the manifold. A "zone" one or more "loops" off a common manifold and controlled by a thermostat. In my shop, there are two zones: one has 4 loops and one has 3 loops. The 4 looper covers 1400 sq ft and the 3 looper covers 1000 sq ft.

Before signing the contract for the system, I spent several evenings on the net where there is a ton of info on various systems. One thing that was common was copper is definitely the best tube for circulating the water: flexible, sturdy, and the best heat transfer rating PEC is the 2nd choice and the only reason I used it was the terrible price of copper tubing. Using copper would have almost doubled the cost of the system.

The pressure testing of the loops was a local code item, but I would have insisted on it anyway because finding a leak would be a bear and then the repair is not something I would want to do or have done.

Trees
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top