Heating A Pole Barn

I should be starting construction soon on my pole barn, I had to pare the size down to 38' X 28' (unfortunately). I am going with radiant heat in the slab, but I suspect that the amount of time needed to raise the temperature inside the building from a low setting while I'm not in there to a comfortable level may be quite long. I was thinking about also installing cast iron radiators and connecting them to the boiler with zone valves and a separate thermostat.

I also need to know what diameter tubing to place in the floor and how many feet of pipe I would need, is there a formula for calculating this? The interior of the barn will have a height of 10 feet, I plan on installing a ceiling and insulated walls. I was also thinking of adding a small extension on the side of the building to house the boiler, I don't want it in the building itself for safety reasons (old cars full of gas, etc.).

Any comments?

Good site for design help for the DIY'er.
http://www.radiantec.com/index.php

Thanks for the link, looks good.

I used them when I made my radiant system. The one thing I would recommend if installing in a slab is keep each loop under 250', mine at 300' there is a cooler spot towards the end of the loop. Also note that you can not get to close together in-between each loop, but you can get to far apart and never be able to go back and do it over again! Just make sure you insulate as best you can underneath the slab and on the sides to help prevent any heat loss. The thicker the slab the longer it will take to heat up and the longer it will take to cool off.

If you want to heat a building in a hurry you want convection heat, not radiant heat. The radiant in the floor is a good idea up to a point as you suggest. The additional heat needed to bring it up to shirt sleeve comfort in a hurry would best come from a water to air heat exchange. I've got a huge one that was originally a farm milk cooler A/C condensing unit. It's got a 220 volt fan motor. I put a switch on it that allows me to run it on 110 or 220. Obviously it runs much slower on 110 but it's just right after my shop has been warmed up. At full speed it only takes 10-15 minutes to make my 25 x 40 block comfortable.

Be sure to insulate the perimeter of the concrete slab, both the edge and underneath. If there is a possibility that the slab might freeze use a zone with a heat exchanger to isolate the anti-freeze from the rest of the boiler water. If only one portion of the slab might freeze, like near a garage door, you can run your tubing in such a way to transfer heat from interior portions of the slab to the door area. You then run the circulator continuously and the stored up heat in the slab gets transfered to the freeze prone area. Sometime negates the need for anti-freeze when the freeze possibility is a rare event.

I keep my slab in my 40'x60' shop at ~50*. this gives me roughly 35-40* air temps.. depending on the wind and outside temps.. the cars, tools and equipement stay roughly at the floor temp.. this is a very comfortable shop.. If I'm going to be out there for an extended period of time, I have a waste oil furnace that I fire up and burn mostly ATF in it,, some engine oil, but I generate 150 gallons a year of ATF in my automatic truck transmission business.

I also have a Modine water to air heater, on the shop floor, I never hooked it up. I probably will eventually put it inline with the slab heat..with a few diverter valves..

Greg L.

Thanks for the pointers. I will only have 1 chance to do this, so I would like to get it right.

I read somewhere that the loops of pipe should be under 200', mine vary from 180 to 200'. The water in the tube has given up too much heat to the slab if the run is too much longer...

Greg L

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Greg,
That really is dependent on how cold the slab is when you are sending heat liquid through the tubes. An ice cold slab will take a lot more heat from the tubes causing the end temperature to be a lot lower then say when you are pumping heated liquid in a warm slab. A variable circulator pump will help you to fine tune the return heat's temperature with temperature gauges on both the feed and return manifold. On mine the more I have warm spots the more I can feel cold spots.


The thicker the slab the longer it will hold heat. The guy at radiantec told me that on very cold nights when it's going to be below zero will turn up his slab a little higher (74*) in case they loose power, because he says his slab will continue to give off heat up to 48 hours later. But it's all because of a 6" slab that is very well insulated. Told me how they lost power and how some of his neighbors had to leave their houses because they had no heat only to return to a house with frozen pipes, him and his family didn't have to leave their house.

Of course there are lots of variables.. but if you have too long a run of tube, and have to increase the circulation rate then you will also have hot spots at the begining of the long run, too much heat in the slab. when trying to eliminate a cold spot at the end of the loop.. Nobody starts with an ice cold slab.. unless it is after a long power outage or a late season start.. I start heating my slab in November, when it gets near freezing at night.. there is very little heat needed to raise the slab temp to 50* then, and then I maintain it all season long.

I don't have separate circulators for each loop, I have a balancing manifold and a single circulator.. each loop is between 180' and 200', and all the return water is within 5* of each other loop.. it is balanced very well.

The slab is 6" thick in most areas, 8" under my hoist pads and around built in hard points in the floor. The perimeter is insulated down to 24" with 4" thick foam and the underside of the slab is on plastic sheet and 1" foam..

It's done right. It's a shop. If I had been creating heat for a home, I would have had to narrow the spacing of the tubes and increase the number of loops to create more heat in the floor... But it functions perfectly for my application.

Greg L.

Nice job Greg, sounds like you set your's up the correct way.

The biggest problem is that it is a big slab, and while it is well insulated, when the temp is cold, it takes some BTUs to keep the slab warm.. but this is the only way to have a shop,, you can't let the shop get to 15* inside, and then go out and expect to work for a few hours comfortably.. every piece of steel, every tool, every machine, Lathe, Drill press, air compressor etc is way to cold to do it's job correctly...

So then when you go to raise the temp in the shop, with a big convective heater, you get moisture/condensation on everything,, the very thing you don't want.. a tool box drawer full of tools dripping with condensation... UGHH.

So it is an expense to keep the shop at 35-40* with the warm slab,, but it sure makes for a comfotable place to go work..

Too bad I live so far north,, If I lived in a more temperate climate I could have a huge shop for less $$..

Greg L

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I am noting all this information, I think a combination of the heated slab and radiators will do the trick for me, I don't like the hot weather, but being able to keep the shop at 55 to 60 during the dead of winter is an idea I like. The problem with an unheated slab is no matter how hot you get the air in the place there is always a layer of cold air by the floor.

Good choice. Position your radiators so you can get a portable box fan behind them to distribute the heat when needed.

Wood,

I was looking at maybe adding two of these to our addition to help to introduce heat into that one room.http://www.houseneeds.com/shop/HeatingP ... ctmain.asp I have two loops under the floor and was going to splice one into each loop keeping each circuit the same length. Was simply allow the water to flow at the end of each loop after the heat had already warmed up the floor.