# Radiant Heating - In-Floor, Hot Water



## RinBarrett (Apr 14, 2015)

Does anyone have experience with heating their shop with in-floor hot water radiant heating? I'm building a new shop in Utah and am considering it. Out here they heat driveways and walkways with it in large commercial applications to help clear snow. So I'm thinking I could use the same technology to bury hot water pipes in my concrete floor and heat the shop that way. I'm thinking it would be a more consistent heat and that it would get rid of the biggest heat sink I have in my shop now, which is the concrete slab sucking the heat back into the ground. I have no idea the cost of operation compared to forced air or other heating methods, but I'm thinking it would be cheaper in the long run. That's something I need to look into.

Any thoughts?


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## ROB_IN_MN (Jul 10, 2012)

i have in-floor heat in my shop. It's awesome, although I'm told it is not the cheapest way to heat a shop.

your foundation will have to be planned out from the start for it. you have to insulate underneath the slap, or like you said, all your heat will be leeched away by the ground.

the install and operating cost is more than traditional heating, but certainly something a non-commercial entity can afford.

keep in mind that the heat buildup and fall off are very long for this type of heat. so, there's no point in things like programmable thermostats.


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## AandCstyle (Mar 21, 2012)

Rin, I have had in-floor radiant in the shop twice. I think it is great; no more cold feet on the concrete floor, no more cold tools, no more condensation on cast iron (maybe not an issue in Utah), etc. By all means put insulation under it and maybe a vapor barrier. I believe that it is more efficient that hot air because it heats things and not air; you don't end up with all the warmth by the ceiling. Also, you don't have to be concerned about shop dust getting into your heating system like you would with forced air. On the flip side, there isn't any duct work for summer cooling. PEX tubing is easy to work, but be careful to not create any kinks in it. HTH


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## shawnn (Aug 30, 2014)

There's a lot of good info at garagejournal.com. I insulated my shop floor before pouring and put PEX loops in, still waiting to wall off the woodshop side & cover/insulate ceiling & walls before trying to install a heater.


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## gerrym526 (Dec 22, 2007)

I'm designing my shop, which will be built next year, and researched how it will be heated. I live in northern Idaho, so it gets cold here in the winter.
Here's what I found doing my research, and what heating unit will be used-
1) Hydronic heating systems are expensive to install and expensive to maintain-you need a furnace, hot water boiler, circulation pumps, manifolds, piping, etc. If one pump fails your looking at $300 for a new one.
2) During spring and fall seasons, when the morning starts out cold (e.g. 40 degrees) but the afternoon warms up quickly (say to 60-70 degrees) your hydronic heating system is out of synch with the temperature. It takes several hours to heat up the concrete slab -you're cold in the morning to start-and then when it's putting out heat in the warmer temp in the afternoon-you're sweating! What you really want is a heating system that warms the shop quickly in the morning when it's cold, but you can shut off before the afternoon warmer temp arrives-keeping you comfortable.

My heating system in the new shop will be a forced air propane heater (ceiling or wall mounted) with an enclosed combustion chamber to make it explosion/fire proof (Modine makes a model call the Hot Dawg). Simple to install, operate and maintain, and heats the shop fast when you need it on a cold morning. Also much cheaper than a hydronic system by orders of magnitude.

I lived in the Chicago area all my life before moving to Idaho, and the winters there are brutal compared to where I live now. In the Great Lakes, the vast majority of houses and shops are heated with forced air units. Hydronic seems to be way more popular in the West, but personally, I couldn't see any advantages to it over forced air, especially when it comes to costs.

On a side note, when you pour your next concrete slab floor, research using closed cell foam slabs on top of gravel and a vapor barrier. You'll find that the "heat sink" problem goes away. And, to get the ultimate in comfort from your floor, I'd put down furring strips covered with OSB flooring-your feet, knees, legs, and back will thank you.

Hope this helps.
Gerry


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## JAAune (Jan 22, 2012)

I've worked in a shop with in-floor boiler heat and now have one with forced air. I'd take the boiler any day. It's far more comfortable than the on/off hot air system. The forced-air furnace seems to dry out the air a lot more. It also also messes up the airflow around my edge sander (which is in front of the hanging furnace) and blows dust away from the collection port and spreads it around.

The increased efficiency of the boiler should pay off over time. It's far easier to heat water (a natural conductor) than it is to heat air (a natural insulator) The landlord that owned the boiler-heated building was happy with the cost of his gas bill but I never saw it and can't compare it to my own heating bill.


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## Picklehead (Feb 12, 2013)

I have radiant hydronic in the floor of my shop. Love it. Leave it set at about 58 year round (in NH). Keeps shop and ALL the tools warm and dry.


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## Manitario (Jul 4, 2010)

I am going into my 2nd winter with in floor heat; I've previously had shops with forced air heat. It is a nice, comfortable heat, and I don't have to worry about forced air blowing the dust around when I'm doing finishing. It does take a bit of planning during construction and a programmable thermostat; it is slow to heat so you can't just go out into the shop and turn up the heat and expect it to be warm in 30 min.


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## DirtyMike (Dec 6, 2015)

Nice smallie,Pickle. If your shop has access to the southern sun you should consider a solar boiler. While im sure the upfront cost are not cheap, you would be self sufficient.


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## TFA (Oct 4, 2016)

in-slab radiant heat is a great option. As many people stated you need 2" sheet of xps insulation and a vapor barrier (6 mil) under the slab to not lose heat to the ground and not take in moisture from the ground. XPS sheets are +/- $1 sq. ft.. you can find the stuff cheaper if you can get it from a salvage place (there's tons of these places out there with insulation in 'like new' condition.) It's also a good idea to wrap the vapor barrier and insulation up the foundation walls if you're in a basement condition (vapor barrier should be continuous under the slab and foundation wall).

Also, as many people said I wouldn't suggest using radiant heat in the slab if you plan on turning the temp up and down based on when you are in the shop.

pex tubing is great for running the radiant heat and it also easily fits into the same clips that are used for rebar so you can clip the pex tubing directly to the rebar making for a really easy installation. You can then pay a plumber to come in and install the pumps and stuff if you need to.


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## canadianchips (Mar 12, 2010)

In floor radiant heat ! 
OF COURSE.
I have had 3 different shops in Northern Canada. winters are a bit COLD !
First in floor heat was put in IHC dealership in 1970. Back then they used 1 1/2" black water pipe. Huge boiler.
Fortunately he did put in header system. They re still using that heat today.
2nd large floor heat was in Lacombe Alberta. Truck wash. One side had radiant heat (JOKE) the other side had in floor. The employees used to fight over who got to work on in floor heat side. Recovery time was quicker than radiant side.
Technology has significant changed in last few years. Smaller boilers, better zoning valves.
Cost to put radiant heat in floor is MUCH cheaper than forced air.
Hot air rises naturally…..heat the floor and the rest of room stays warm.
ONE note. You can set thermostat 10-15 degrees lower with floor heat .
Im still sitting on fence about insulating floor…....I would insulate 2ft around perimeter…..not sure I would go extra cost of insulating entire floor.


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## shampeon (Jun 3, 2012)

I live in an Eichler house, built in the late '50s, with radiant heat in the slab. It's really nice. Luckily our home used copper pipe, unlike a lot of other houses built earlier in the '50s that used black water pipe. The black pipe will fail eventually, causing slab leaks. Detecting and fixing slab leaks is expensive, so a lot of owners just cap off the radiant system and install forced air.

We use a smart thermostat (an Ecobee 3) that learns how to most efficiently turn on/off the boiler to maintain the temperature schedule we set.

I've also seen electric radiant heat that goes below the subfloor on top of the slab.


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## RinBarrett (Apr 14, 2015)

I've heard of electric radiant heat. I wonder if it's more responsive to temperature change than water. One of the issues raised is that turning the heat up and down takes time. I don't spend that much time in my home shop so turning up the temp when I want to work for a few hours then down after I quit is a good thing.


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## TFA (Oct 4, 2016)

It's not the water that doesn't change temperature quickly. It's the fact that you have to heat up the concrete slab. That slab is 150lbs for every 2-3sq. ft.. It's a lot of mass to heat up every time you enter the shop.

Another thing that you could do with the radiant is to move the insulation above the slab, then put your radiant on top of the insulation, then lay your sub-floor and finish floor over the radiant. That way each time you turn on the heat you're only heating up the wood subfloor and finished floor. You can buy plastic sheets that the radiant tube snaps into and sets up a good base for the subfloor. You will still want a vapor barrier under the slab though.


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## AandCstyle (Mar 21, 2012)

Rin, electric is the most expensive way to heat. I found that I could set my thermostat at 50° and leave it. That is warm enough when you are working, but not too warm so you are wasting a lot of energy. FWIW


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## rad457 (Jun 15, 2013)

I have a stand alone 600 sq/ft shop 10ft walls with a 8' x16' garage door, I'm heating it with a 20 amp. electric boiler, (pulls an average of 8 amps this time of year) with in slab pex tubing. Had to turn the boiler up this week as it is dropping to - 30 deg. C ( F and C meet at -40) at night at the moment. I have 2" H.D. foam below the slab and put 1,5" 24" deep Vertical around perimeter to create a heatsink. Frost/cold travels below grade at 45 degrees. I live north of Edmonton Alberta Canada and does get a little cool this time of the year. Overall the cost is very low, I suspect less than an Hot tub?


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## TajBuilder (Aug 6, 2008)

A concrete floor is a big heat sink if its allowed to get cold and freeze. But it can also store a lot of heat if its not allowed to cool. The biggest advantage of radiant heat over forced air is that it heats the objects in the room instead of the air. Since solids store more heat than air, radiant heat has the potential to be more efficient.

I also considered in-floor radiant heat when I built my shop but settled on a suspended radiant heat tube like those found in aircraft hangers and garages. My shop is 30' x 40' with 8' walls and scissor trusses that are 16' at the peak. The natural gas heat tube is 20' long and is mounted in the center of the building about two to three feet from the peak so it reflects heat off both sides of the ceiling. It pulls combustion air from one end of the building and exhausts out the other. I didn't insulate underneath the slab so I could take advantage of the relatively constant temperature of the earth. Instead, I insulated around the footing. I've since read an article on frost free slabs that says you should insulate by burying foam panels horizontally with a slight downward slope around the perimeter because frost travels vertically and not horizontally. I also buried my dust collection, electrical and water lines before I poured the slab.

As was stated above, radiant heat works best at maintaining a constant temperature. I set my thermostat around 45-50 which is very comfortable for working. It doesn't take long to raise the temperature if I decide to sit down and watch a ball game or have something to paint.


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## Pogo930 (Aug 21, 2016)

Friend has a 24 X 24 shop with in floor. Not sure how much underfloor insulation. He uses an electric hot water heater. He says it costs just a few dollars a month (under ten). I would have done the same except the fill, I'm on a slope, would have cost as much as the concrete. Went with wood over a crawl space and hot air.


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## canadianchips (Mar 12, 2010)

Good info about floor heating !
http://www.healthyheating.com/downloads/22%20Myths%20about%20radiant%20heating.pdf
Check out myth #25
as well as 29
Myth #29
"Under slab insulation does not force heat up to the floor surface nor block it from going down nor does it reflect cold nor is the heat within a concrete slab being transferred by radiation…insulation is resistance…it slows or impedes the flow of energy in the form of heat travelling from hot to cold via conduction…radiation only comes to play at the uppermost surface of the floor. Learn more about reflective insulation scams."


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## canadianchips (Mar 12, 2010)

Also. Pex pipe in Canada is about .67 ft.
Put the pie in the floor now, later you can connect it if you decide.


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## MinnesotaMarty (Jan 25, 2015)

> Also. Pex pipe inbu Canada is about .67 ft.
> Put the pie in the floor now, later you can connect it if you decide.
> 
> - canadianchips


canadianchips, 
I am with you man. i have owned three shops now in my life. One with forced air hanging heaters (cheap to install) and one with with a wood burning forced air furnace, (simply because I had a wooded homestead and needed a place to get rid of all the wood around me. I use a hanging heater as a standby. Finally, I got the shop with in-floor heat with a nat. gas fired boiler. I have it zoned separately and have the thermostat set at 45 degrees- Fahrenheit. This shop is attached to my house so it was a no brainer. 
I agree if you are building install the pex, its there if you want to use it. I insulated under the slab and around the perimeter of the foundation. I am of the" thought school" to stop the cold from ever entering the heated space. 
Marty


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## them700project (Aug 12, 2015)

As a mechanical contractor I would highly recommend it. It is cheaper in the long run to run but the initial cost is much higher. The big advantage is you are not running boiler at 160-170 , it will run at 110 which is far more efficiant. Forced air will heat the ceiling and work its way down


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## TajBuilder (Aug 6, 2008)

I stand corrected. Insulation is required under in-floor heating but not necessarily for overhead heat tubes depending on the climate zone. In my area the uninsulated slab except for the perimeter provides a thermal mass to help cool the shop in the summer because of the ambient temperature of the earth.


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