Garage heat

[Engineer]

Trying to plan heat for my new garage in the spring.  All I know for sure is that I am putting PEX tubing in the slab, just like my house.  What I am not sure of, is how to supply the heat.  My OWB is about 120 feet away in a straight line, which means at $14/ft, ThermoPex is $1700 plus the cost of digging and backfilling.  Lets round it off to an even $2500 by the time I'm all done, connected to the OWB and the garage manifold.  That will buy me a nice heat pump or small instant-on electric water heater, and considering I will only need the garage at about 50-55 degrees, I am not sure it is economical to run the PEX from my boiler.  I am also considering one of those hotel-style heat pumps that both heat and cool the air, but that does not provide for a warm floor, which to me is essential.  I couldn't work in a shop without the floor being heated, I'm spoiled by the basement in my house.  I should also add that the garage will not have a water supply, so whatever I put in will have to be a closed, pressurized loop system.  If I need to add water I will have to run a hose from my house (which is only 50 feet away).

Are there other reasonably-priced options that will supply warm water to a radiant loop system?

[Ford_man]

Check www.houseneeds.com  They are a lot cheaper than what your looking at.

[gspren]

   I don't know what your building lay out is but could you run pex from house to garage? The water from your home return is probably plenty hot to warm the garage.

[Engineer]

   I don't know what your building lay out is but could you run pex from house to garage? The water from your home return is probably plenty hot to warm the garage.

Building layout does not support this idea, although the theory is fine.  I'd probably be better off relocating the OWB.  I had a different location planned for the garage when I built my house, which would have meant a run of only 40 feet or so.

[LittleJohn]

You could even use a hot water heater, for the garge.  Also most slabs only require maybe 120F water, and unless you are building a MONSTER garage, I think it should be able to keep up, until you can afford to trench in the expensive stuff  ;)

[WmFritz]

  I should also add that the garage will not have a water supply, so whatever I put in will have to be a closed, pressurized loop system.  If I need to add water I will have to run a hose from my house (which is only 50 feet away).

Are there other reasonably-priced options that will supply warm water to a radiant loop system?

How is your boiler set up for makeup water? Your added lines can filled at the boiler can't it?
A closed system is easy enough to design with a water to water H/X.

A cousin of mine is heating a 40x50 slab with a gas 40 gallon hot water heater. I can't remember the exact number, but he put at least 3" of foam under it. About 6 or 7 years ago we were discussing his system. He keeps the T-Stat at 50° all winter and was averaging about $1.50 per day to heat it in Mid-Michigan back then.

[bandmiller2]

Engineer, are you planning to work in the garage or just park equipment in it.?? A regular old wood stove will take the curse off the cold in a short time. If you have water in the floor you will always have the worry of it freezing, unless you antifreeze it. My machine shop has an old pot belly stove and heats fast with a few wood scraps. Frank C.

[xalexjx]

make sure you put down 2" insulation under concrete

[Engineer]

Engineer, are you planning to work in the garage or just park equipment in it.??

This is going to be my workshop/woodshop, and will be occupied, if only for a few minutes, almost every day.  I want to use radiant heat and dehumidification/air conditioning, and appropriate temperature control, in order to keep equipment in top operating condition and accommodate drying time for finishes.  If this was just a vehicle garage I'd toss in a Modine Hot Dawg or equivalent, and be done.

[VTwoodworker]

I heat my garage that is 28x38 with radiant in the floor.  There is an apartment on the second floor.  I heat the garage to 50 deg.  I heated the building upstairs and the garage for one season before installing the outdoor boiler and we used around 800 gallons of propane.  The building is well insulated as well as under the slab.  I have no way of knowing how much the garage required of the total but I estimate it would be 60%. 

I now heat the garage from the wood boiler and I know by the wood usage when the slab is being heated.  I burn a lot more wood.  I have 3 decent garage doors and you do what you can but a lot of heat is lost.  Cars and tractors come in covered with ice and snow and in the morning they are thawed and dry.  I personally would not use a hot water heater for this application and based on my experience it would be worth investing in the thermopex. 

I cut my wood so all I have in the cost is labor.  If you are buying wood that will affect the cost equation.

I love my radiant heat.

[Holmes]

 You will kick yourself if you do not do the radiant heat.   Buy the cheaper insulated pex and add 1" blue or pink insulation board cut in 8" width around it in the trench. Adds r5 to the heat loss value.

[thecfarm]

The warm floor is nice. Would it matter when you open the door and bring in something cold on how long it takes to warm back up? Would modine heater help with that? 

[Engineer]

Well, I've got the radiant slab in the basement of my house and it is a walkout basement.  Even in some of the lowest temperatures this past winter, we can leave the door open to bring in groceries or what have you, and once you close the door, there's no lingering chill like you'd find in a non-heated basement. 

I definitely plan on doing the radiant slab, that was never any question.  What I am unsure of is the method for heating the water (or antifreeze) in the tubing.  Considering I did not have enough time last year to harvest enough wood just for the house, I am worried that the wood consumption will increase to a point where I can't keep up with it.  I've never bought wood but I am considering a truckload of log-length wood every year as a supplement to what I have time to harvest in the woods.  It's a lot easier to just stand there and cut and split - going through the woods and finding trees, dropping them, bucking them and bringing them back home takes a lot of time.

One idea that I saw on another site is carefully digging a narrow trench, lining it with plastic and Styrofoam, and them using spray foam to fill the Styrofoam "trough" before backfilling.  It's cost effective but I worry about contact with groundwater, which will effectively short-circuit the heat right into the ground and I will be using a lot more wood than necessary.

[pabst79]

 Never tried the spray foam, use at least 2" board under the slab and hold your tubing 8-12" from the edge, use 2" board on end to meet the board under the slab + plastic, and you won't lose heat out the side of slab, I have seen a few homeowners forget this step and honest to God sometimes the snow will be melted 8' out from the walls, what a waste! For customers that don't want to spend the money on a gas fired boiler or the expense of heat ex and tubing to their wood boiler, a res type 40-50 gal gas water heater will keep a 30x40 shop 60 degrees plus for a very reasonable amount. Most manufacturers make water heaters with side taps for space heating.   I heated my house which is 40x80 slab on grade, with a 75 gallon for 3 years before I put in a gas and wood boiler. That wasn't very cheap, LP man was happy. :D

[beenthere]

Engineer
With your plan of the new garage, have you figured in the cost/benefit of a second OWB set up near the new garage?  Removes the 120' trench/piping. But realize there are other considerations.

I would have some backup system to use when the OWB cannot be used as well.

[WmFritz]

I thought about mentioning this right off the bat, but I'm early in my planning and don't have all my figures yet. Holmes touched on it and now your studying on it, so I'll throw out here the way I'm going to do my underground.

I need 1 1/4" supply/return lines to run into the existing radiant system I have. I set it up 4 years ago with a propane on-demand hot water heater with the intent on buying a boiler when the funds permit. I'm getting it off the propane this year.

I don't have a set length for my trench yet ( I'm waiting for the Spring thaw to pull my measurements), but I'm thinking my boiler will be 60' away. I will do do foam in trench. I'll make 3 sided 'forms' from closed cell foam sheets. If I rip an 8' sheet into 8" wide pieces, then 1 sheet would go 16' long.  I'll foam it in with kit like this...

https://www.menards.com/main/paint/caulking-sealants/foam-sealant-and-insulation/froth-pak-200-foam-sealant/p-1625330-c-7937.htm

The foam MUST be closed cell to block moisture. I'll spray in an inch or two of foam then lay in the Pex and fill it all in with foam to the top of the form. A 350 board foot kit would be plenty and I think I've seen them selling for around $350.00. That would get me roughly 10"x10" of insulation around the lines. I may line the trench with 20 mil plastic first to keep the dirt out of the foam, but will decide that later. I don't think its needed for water protection.

The best price I've found so far on the 1 1/4" pex is here...

http://www.freeheat4u.com/1-14-Uninsulated-02-Barrier-line_p_57.html

So, I'm figuring for about $800.00 in materials. If I were to purchase the 1 1/4" already insulated I think it runs $20-22 per foot. The foam in trench will have much better r-value for  less $$$.

[magicmikey]

  Engineer
     I have a 25 x 55 garage with infloor heat and used 2" closed cell sheets for insulation under and around with some 4' high concrete stub walls also. The styro  meets at the footing,runs 6" up onto the stud wall around the entire perimeter and is capped with a 45* split 2" x 2" board. A 2' strip of PT plywood protects the styro on the outside with siding overtop. All the concrete now becomes a heat sink.

  Here footings must have a drainage system to remove any water from the area. For slab on grade frost protection is also a requirement [ don`t know about Vt. ]

  One learning from my experience is about ventilation. The air in the building is in constant motion and any contaminates stay in suspension. In my case it is welding smoke which will linger for about 2 days, of course opening the rollup door for 5 minutes eliminates this.

Just my thoughts.
mike

[mapleveneer]

I would be careful about taking shortcuts with the insulated underground piping.  The last thing that you want to have to do in January is to have to dig this up.  When it fails, you really have no other option.  Call around for prices on the foam-insulated PEX supply and return piping.  I used 1 in. in 2012 and got prices that ranged from around $10/ft. to $20/ft. Got mine from Mainline Plumbing, Ashford, CT.

[47sawdust]

Engineer,
Since someone brought up the idea of a 2nd heat source,you might check out NWCT CL.(wood boiler).There are a couple that might be worth looking at.The Thermo-control boiler is made in N,Y..the other one ($3000.00) unused was made by THE FURNACE WORKS in Minnesota.They have a very good reputation.Forum member Beenthere has one and if you do a seach ther is an old thread about that brand,also pics in his gallery.

[beenthere]

Yes, I have the Furnace Works indoor boiler, bought in 1980 for $800. Company has been out of business since the eighty's. 

[LAZERDAN]

WmFritz
Whatever you do don't cheep out. I would strongly advise you not to use your plan.  I did ( because I did not have the money back then ) Big mistake. Really not that big ,just an extra 6 cord per year for the last 7 years. Get the thermo pex it's bullet proof. There an older thread I had a long rant about my stupidty, you could search.  Just trying to help      Lazerdan

[Mn woodchuck]

I have been heating my shop 40x70 16 'side wall for 25years with a lp
water heater in floor radiant heat . I try to keep it 40*f in there it takes 800 to 1000 gals of lp per winter. The last 3 years I put in a wood burner stove to keep cost down and heat up. The lp was (is) killing me. I would like to go to a OWB and also want to heat the house with it so I'm kinda in the same spot you are ..I love the floor heat   contrary to some opinions I hardly notice when opening the large overhead doors to move stuff in or out   Even bringing in a combine it still seemed to hold the heat well. The 80,000 btu water heater can barely keep up on the coolest days  (0 and below.)
I m planning to run my hot water threw a air to air heat exchanger then threw the floor tubes and back to boiler separate runs for house and shop. I t really sounds like thermoplex is the only way to go.

[WmFritz]

Lazerdan,
Are you you saying you used you sprayed in foam and it failed? Without knowing your installation, I can't speak to that. 1 cord of wood wasted is too much... 6 is a big deal. If I'm reading you right, you switched out your underground and cut your wood use by 6 cords? I know Therm-Pex is proven and reliable.

To be honest, it would be way simpler for me to run a trench and drop a Thermo-Pex line in.  For that reason, I'm not recommending foam-in-trench.  I shared my plan because Engineer was looking for ideas. I'm not using foam-in-trench to cheap out. Cost isn't my main motivation. I'm confident that foaming my lines in will work for me. I've seen one installation first hand and if I can achieve anything as close in efficiency as that one, I predict less then 2° f loss total on my supply/return lines.

[LAZERDAN]

 WmFritz
Ya  I guess i'm kinda vague,  I am only trying to tell you it's alota work to dink around and try to build the perfect or better insulated line.  I dug a really deep
trench, the ground was so hard and tight when it rained the trench filled and stayed filled, dug a trench along side deeper to drain the main trench and put in a manhole for a pump, to pump out the backyard.  Theres more, but I gotta go.  I'm just trying to tell you how amazed I Was with the Therm pex, It can lay on the ground in -30 and no snow melt at all.  May- be cheep out was i'll chozen words.  Foaming is great if you plan is perfect.  I'll be back to continue     Lazerdan