Radiant floor system

[bepjrfan]

Guys,

Been lurking around on this site for the past year, dont post much. Got some good news, finally got the approval from the boss to build my dream garage! 28x32 with 10 ft walls. Working on plans at the moment here, waiting on bids on concrete as well. The big decision I have at the moment is heating. I live up in North Dakota where it gets pretty dang cold in the winter time, trying to decide between a gas hot dawg similar to what my parents run or to go all out and run with a radiant floor heat system.

I know if money was no object, most people would put floor heat in but it looks as though I'm going to have to pony up about $3-3500 to run floor heat vs ~$7-800 for a Hot Dawg gas heater. Is there much cost savings down the road running floor heat? Or would I be fine to go with the hot dawg setup?

 

[Randy in Maine]

My garage is pretty close to my house (about 20 feet) and I am able to tap into my house boiler to run my radiant floor heat. That helped save me a lot of money. The 1000' of 1/2" pex, the 2 four tube manifolds, the thermostat, and the 3/4" pex to get water in and out of there was all that was needed for me.

The radiant floor heat in the insulated concrete mostly gives you a lot of thermal mass that is able to maintain a constant temp with little additional BTU input. How well you are insulated and how limited the infiltration of the building is what keeps the temp maintained.

That being said, I keep my floors out there heated to maintain a 50º air temp. I pump out water to the shop at about 120º and it comes back at about 90º. My shop (made out of SIPS) is about R-40 or better and built as tight as I could make it. I am not able to figure out how just often the shop heat runs, but it is as good as I can get it.

 

[bepjrfan]

What kind of cost increase did you see on your monthly utility bill with the garage added? If you don't mind me asking.

 

[Gooch]

Your btu load doesn't change with the heat source. If you need 20k btu. It doesn't care where it comes from. If you're going to use a 67% effective. Water heater you are probably better off with the hot Dawg. If your gonna pony up for a 95% effective. Boiler then that changes it. The heating source just changes how the system behaves. Forced air has more peaks and Valleys temp wise and you have moving air. Hydronic tends to be more stable and gradual with no air movement

 

[Randy in Maine]

What kind of cost increase did you see on your monthly utility bill with the garage added? If you don't mind me asking.

Kind of hard to say in my case. As I was building the 40'28'12' garage, I also added radiant heat, windows, frenchdoors, and insulation to the attached 23'x12' garage (now my wife's stained glass workroom), and put 6" of closed cell spray foam in the ceiling of our 28' 32' log house and radiant floor heat in the whole house. I also insulated my crawl space with 2" of rigid foam. Mostly a lot more comfortable and constant. No more frozen pipes.

I now have a nice 5 burner gas kitchen stove and my domestic hot water comes from the same Baxi boiler that provides the radiant heat. When the existing dryer goes, I will replace it with a gas one. I also have 2 propone fired woodstoves as my wife likes them and it will warm up the house or her workshop quickly if she want it.

Before all of that and building the garage I used about 650 gallons of propane in my house propane fired woodstove every year. Now I use about 600 gallons of propane every year. For me that is still about $1200-1400 a year.

I still think the common sense way to do it is to super insulate first.

 

[bepjrfan]

Your btu load doesn't change with the heat source. If you need 20k btu. It doesn't care where it comes from. If you're going to use a 67% effective. Water heater you are probably better off with the hot Dawg. If your gonna pony up for a 95% effective. Boiler then that changes it. The heating source just changes how the system behaves. Forced air has more peaks and Valleys temp wise and you have moving air. Hydronic tends to be more stable and gradual with no air movement

Planning on going with a boiler system with a floor heat setup., just been impossible to find the correct information online as far as all the components needed. I see northern tool has a full system minus PEX for $2300. I need 20k btu from what I've been figuring. Been tough finding the pricing for everything needed is the issue I'm running into.

 

[Gooch]

Planning on going with a boiler system with a floor heat setup., just been impossible to find the correct information online as far as all the components needed. I see northern tool has a full system minus PEX for $2300. I need 20k btu from what I've been figuring. Been tough finding the pricing for everything needed is the issue I'm running into.

I wouldn't buy a boiler from northern tool. That's an electric boiler, I'd avoid that like the plauge. Electricity is really expensive compared to gas(natural or Propane)

 

[theoldwizard1]

The primary reason most people install radiant in-floor heat is COMFORT ! If you plan to spend a lot of time in the garage, now and in the future, you will be happier.

A few things contribute to the "cost of operation" of any heating solution

• Fuel cost/BTU. Electric is the highest, wood (if you cut it yourself) is the lowest.
• Number of heating hours per season. High installed costs will take longer to pay back.
• Insulation. "You pay for insulation once. You pay for heating fuel every time the thermostat calls for it !"

FYI, the cheapest "cost of operation" heating solution is a ground water source heat pump. It is also the most expensive to install.

 

[rburke65]

Wizard.....what do you pay per KWhr?

 

[Streetbu]

How much room do you have? IE Land? Could you do a geothermal? If you have equipment and time the pipe is cheap... thats almost free heat. I have heard of people even just burying the pipe, putting the PEX in the slab, then filling the system with water and using a pump to circulate it. Wouldnt be very warm but should keep it above freezing at the least. Better than nothing

 

[jameslinn83]

My opinion, go with in floor if you plan on spending any amount of time in the garage. I'm in mn and have a hot ********* in my 24x36. It heats it up fine but my feet are cold as the slab is still cold. I spend all day out there and am getting in floor in my next garage. Also the heater is b vent do it draws air from the garage to burn and that air needs to come from somewhere so it's pulling cold air in through any crack in the garage it can find every time it runs , probably another contributing factor to cold feet. With in floor heat there is no air movement so unless you open a door you not letting cold air in. One benefit to hanging heater is that it pulls the moisture out nicely vs in floor alone if your bringing wet or snowy vehicles.
If you use a direct vent hanging heater none of that applies because those don't exchange any air with the room besides radiant heat.
No matter which way you go insulate the slab and put in the water lines so you can add in floor if you decide to.

Sent from my SM-N910V using Tapatalk

 

[jameslinn83]

I should note I have a buddy with a 40x80 and 40x40 of it is on a heated floor slab with a reznor heater. He keeps the slab with in floor heat around 40-45 and just bumps the reznor up when he goes out there. Which is mainly only weekends and occasional evening. This would be my ideal setup except maybe with the addition on a wood stove to use if propane is spendy or I have wood to burn. But I like wood heat

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[finn]

I should note I have a buddy with a 40x80 and 40x40 of it is on a heated floor slab with a reznor heater. He keeps the slab with in floor heat around 40-45 and just bumps the reznor up when he goes out there. Which is mainly only weekends and occasional evening. This would be my ideal setup except maybe with the addition on a wood stove to use if propane is spendy or I have wood to burn. But I like wood heat

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That's exactly what I do.

I can't afford to keep my shop at working temps 24/7 with the floor heat alone, so I set the boiler thermostat to about 42 degrees, but fire up the hanging furnace when I'm working out there. It takes less than thirty minutes to bring the air temperature from 42 degrees to 62-65, which is warm enough since the floor is above freezing.

 

[bzinsky]

Your btu load doesn't change with the heat source. If you need 20k btu. It doesn't care where it comes from. If you're going to use a 67% effective. Water heater you are probably better off with the hot Dawg. If your gonna pony up for a 95% effective. Boiler then that changes it. The heating source just changes how the system behaves. Forced air has more peaks and Valleys temp wise and you have moving air. Hydronic tends to be more stable and gradual with no air movement

Hydronic in-floor is actually more efficient

Boil a pot of water on a gas stove, it gets warm very quick, and then takes a really long time to boil. Something cold will absorb more heat than something hot.

This is how hydronic systems work, whether you have cast iron radiators or in floor. In floor heat has a lot of surface area, which allows you to keep the circulating water temperatures low, which allows the water to absorb the heat from the flame more efficiently. You could do the same thing by putting in tons of radiators, but that has obvious drawbacks.

That being said, as someone has already stated, in-floor hydronic in a concrete slab garage also has a boat load of thermal mass, and if you just need heat to go in there and work on something and not maintain a steady temp it will waste a lot more than it saves in efficiency.

 

[yeldogt]

My garage is pretty close to my house (about 20 feet) and I am able to tap into my house boiler to run my radiant floor heat. That helped save me a lot of money. The 1000' of 1/2" pex, the 2 four tube manifolds, the thermostat, and the 3/4" pex to get water in and out of there was all that was needed for me.

The radiant floor heat in the insulated concrete mostly gives you a lot of thermal mass that is able to maintain a constant temp with little additional BTU input. How well you are insulated and how limited the infiltration of the building is what keeps the temp maintained.

That being said, I keep my floors out there heated to maintain a 50º air temp. I pump out water to the shop at about 120º and it comes back at about 90º. My shop (made out of SIPS) is about R-40 or better and built as tight as I could make it. I am not able to figure out how just often the shop heat runs, but it is as good as I can get it.

How did you do? Insulated pipe with one or two heat exchangers ... glycol. I could do the same ... all are against ... mostly because no one has done it.

It's amazing how many people in the trades don't or will not change how they do anything.

 

[Randy in Maine]

I am not sure just what your question is.....

I ran my 3/4" pex tubing to the shop in 4" Schedule 40 PVC (buried 4' deep) to and from the 2 manifolds located in the shop in an interior wall. I also ran my hot and cold "domestic water" out there to the same interior wall for the outside sillcocks also in' PVC. My 100 amps of shop power goes to the same wall also underground in its own PVC underground.

I don't run glycol in my system.

1 cubic yard of concrete = about 2 tons of thermal mass. My shop has 21 cubic yards in the floor as it is about 6" thick. Plus everything in the shop is all nice and warm also.

 

[joe--h]

Forget Northern tool. Look here---------> https://www.radiantec.com/

Radiantec has been around a long time. They can design your system and supply everything you need.
And insulate the whole slab.

Joe H

 

[HoosierBuddy]

Soo...a gas fired unit heater like the hot dog is going to be your cheapest option for energy expense IF you only turn it on when you are out there working. Gas unit heaters are really good at bringing a cold space up to a somewhat comfortable temperature relatively quickly....much quicker than a radiant floor system could do it. PLUS...you don't have to worry about a gas unit heater freezing like you would your radiant loops, so leaving it turned to "off" several days a time is no big issue.

So...the CHEAPEST way to heat your building is to do it "part time" and with a heater that doesn't mind sub-freezing temperatures.

Where a radiant system shines is when you don't care as much about total energy cost and DO plan on running your heat 24X7XWinterWeeks and want a super quiet super comfortable heating source...and you're willing to pay extra for it.

Phil

 

[yeldogt]

I am not sure just what your question is.....

I ran my 3/4" pex tubing to the shop in 4" Schedule 40 PVC (buried 4' deep) to and from the 2 manifolds located in the shop in an interior wall. I also ran my hot and cold "domestic water" out there to the same interior wall for the outside sillcocks also in' PVC. My 100 amps of shop power goes to the same wall also underground in its own PVC underground.

I don't run glycol in my system.

1 cubic yard of concrete = about 2 tons of thermal mass. My shop has 21 cubic yards in the floor as it is about 6" thick. Plus everything in the shop is all nice and warm also.

So ..... you did not insulate the PEX leaving the house ......

OH .. maybe the shop is connected to the house. Mine is not -- I'm about 20 feet away.

 

[Randy in Maine]

Not trying to sidetrack the original poster here....

My pex leaving the house for the 20 foot run outside to the detached garage is in PVC pipe in a trench that runs 4' underground. The trench has some 2" scrap insulation on three sides of the trench. I figured that might stop a big freeze with no snow from freezing the pex. It has been OK so far.

To the OP, I would suggest insulating under the slab and at least running the pex tubing inside the slab. That way if you (or the next owner) decide to heat the slab, the hard part will already be done. It could also be a selling point if you end up selling the place.

 

[jack stand]

Lot's of good advice has been given here!
The big "killer" of radiant is the up front, usually when it's warm or hot outside expense of the 2" of rigid foam you need to put under your already expensive concrete! This insulation will benefit you regardless of your eventual heating method. As for prepping it for the radiant (tubing), that's a very small expense, maybe under $500. You can do it yourself. So in the end, the couple grand for insulation that will help you, period, and that leave's you $500 or so invested into radiant...... you could do the "hot dog" cooker for a few years, if you're happy, great. Not so happy, you just add hot water, your choice how you make it but your prior little "investment" of $500 will be paying off.
I would go a step further and insulate (prior to the slab) vertically if your building on a "frost wall" of shallow foundation and the other steps the create a "thermal break" as would be done for radiant heating. You know how concrete ***** the cold right in (side).

 

[theoldwizard1]

At an absolute minimum, install a vapor barrier and insulation under the slab ! It will make a difference in keeping the sub-zero temps from migrating into the building.

How much room do you have? IE Land? Could you do a geothermal? If you have equipment and time the pipe is cheap... that's almost free heat.

Geothermal is VERY expensive to install !! You have to use it a lot to get any kind of reasonable payback.

IMHO, horizontal ground loops are NOT a good idea, especially in climates that can have multiple days in a row of below 0F weather. Wells might cost more to install, but if you have insufficient heat transfer, you can always add another well.

Where a radiant system shines is when you don't care as much about total energy cost and DO plan on running your heat 24X7XWinterWeeks and want a super quiet super comfortable heating source...and you're willing to pay extra for it.

It is not as bad as you make it sound ! You can dial back the temp to 50-55 when you are not there. That will save a HUGE amount.

I am not saying it will be as cheap as a heat source you turn of completely or one that simply blast hot air into an empty space, but it is about COMFORT !

Much better than a hot dawg is a Rinnai direct vent furnace.

 

[rburke65]

Old wizard......what is your cost per KWhr of electricity? Thanks.

 

[n20junkie]

Hydronic in-floor is actually more efficient

Boil a pot of water on a gas stove, it gets warm very quick, and then takes a really long time to boil. Something cold will absorb more heat than something hot.

This is how hydronic systems work, whether you have cast iron radiators or in floor. In floor heat has a lot of surface area, which allows you to keep the circulating water temperatures low, which allows the water to absorb the heat from the flame more efficiently. You could do the same thing by putting in tons of radiators, but that has obvious drawbacks.

That being said, as someone has already stated, in-floor hydronic in a concrete slab garage also has a boat load of thermal mass, and if you just need heat to go in there and work on something and not maintain a steady temp it will waste a lot more than it saves in efficiency.

You still put the heat into the water. BTU is BTU. Yes water has a very high specific heat. But you didn't get any more out of the water than you out into it.

What many fail to consider is the summer. If your going to install an air handler, ducting and AC setup, might as well just add a forced air furnace and call it a day. We have plenty cold temps up here, and I have never had an issue with a cold floor. I have had an issue with an overly warm floor causing me to sweat my *** off while working close to it though.

 

[bzinsky]

You still put the heat into the water. BTU is BTU. Yes water has a very high specific heat. But you didn't get any more out of the water than you out into it.

yes, a btu is a btu, but what your flame produces and what the water absorbs are two different things.

Completely made up figures to make a point

You have a 100k btu gas boiler for your hydronic system

Cold water = 90k btu's being absorbed by the water, 10k btu's going out the exhaust
Hot water = 75k btu's being absorbed by the water, 25k btu's going out the exhaust

You're thinking in terms of electric resistance heat where X watts = Y btu's no matter how you slice it.

With fuel heat, you always have an exhaust, so not only does it matter how many btu's of flame you have, it matters how much of that is absorbed through the water or whatever heat exchanger your system has.

This is exactly why high efficiency water heaters have power vents and PVC exhausts, because the exhaust does not have enough heat to expel itself via "hot air rises" or melt the PVC.

This is also exactly why in-floor systems are efficient, because the cold water allows you to absorb more btu's from the flame.

 

[finn]

Hydronic in-floor is actually more efficient

Boil a pot of water on a gas stove, it gets warm very quick, and then takes a really long time to boil. Something cold will absorb more heat than something hot.

This is how hydronic systems work, whether you have cast iron radiators or in floor. In floor heat has a lot of surface area, which allows you to keep the circulating water temperatures low, which allows the water to absorb the heat from the flame more efficiently. You could do the same thing by putting in tons of radiators, but that has obvious drawbacks.

That being said, as someone has already stated, in-floor hydronic in a concrete slab garage also has a boat load of thermal mass, and if you just need heat to go in there and work on something and not maintain a steady temp it will waste a lot more than it saves in efficiency.

Your time to boil analogy is flawed, because you are ignoring the fact that there is a tremendous increase of energy required when passing through the phase change (liquid to gas) when boiling water as opposed to simply heating a liquid without the phase change.

 

[bzinsky]

Your time to boil analogy is flawed, because you are ignoring the fact that there is a tremendous increase of energy required when passing through the phase change (liquid to gas) when boiling water as opposed to simply heating a liquid without the phase change.

I know, same with ice to liquid or vice versa

I was actually thinking that as I was typing and was going to change it but figured boiling water is just a more commonly used term that's easier to get the point across

 

[Northislander]

if i remember my figures right from trade school 970 btu's per lb. of 212 degree water to steam

 

[bzinsky]

Yeah I wondered for like 15 years why my whiskey stones did hardly anything to cool down a drink compared to ice cubes.

I could not figure it out, thinking those damn stones had to have way more thermal mass than ice, so why did they do nothing??

Then one day someone told me it takes a ton of energy for ice to transition into water, and had one of those ah ha moments immediately picturing my whiskey stones.

 

[jack stand]

Ok with the efficiency talk, isn't part of the efficiency of radiant floors compared to other hot water based heating (baseboard, radiators, a coil in a forced air system) the fact that generally your water temps are down around 110*, way below the temperature needed for the others?

 

[86turbodsl]

Yes, that's also true. Way easier to heat water to 110F or less than 160-180 with a GSHP.

 

[yeldogt]

BUT's are BTU's ... radiant floors put the heat where your body is .....starting at your feet. As the heat rises and cools it's less needed -- ideally the ceilings should be colder. The opposite is true with forced air -- also a huge radiant component with a head floor -- it's a big radiator.

Fewer BTU's are needed to achieve a given comfort level -- also, fewer BTU's in a given space reduce the stack effect.


Lower water temps also also allow the new modern condensing boilers to "condense" -- they require this colder return water to cool the exhaust gas.

Older style cast iron boilers capable of using colder water ( Buderus) -- benefit from the colder operating temps. Lots of heat goes up the flue when running at 180 degrees -- even when the boiler turns off --- with a vent damper .. the stack effect is also at play.

 

[6inarow]

At an absolute minimum, install a vapor barrier and insulation under the slab ! It will make a difference in keeping the sub-zero temps from migrating into the building.



Geothermal is VERY expensive to install !! You have to use it a lot to get any kind of reasonable payback.

IMHO, horizontal ground loops are NOT a good idea, especially in climates that can have multiple days in a row of below 0F weather. Wells might cost more to install, but if you have insufficient heat transfer, you can always add another well.



It is not as bad as you make it sound ! You can dial back the temp to 50-55 when you are not there. That will save a HUGE amount.

I am not saying it will be as cheap as a heat source you turn of completely or one that simply blast hot air into an empty space, but it is about COMFORT !

Much better than a hot dawg is a Rinnai direct vent furnace.

hey Oldwizzard1 have you ever owned or installed geothermal?

 

[Jackfre]

Radiant is great heat and yes it is expensive up front. How do you intend to use the space. Is it a constant and continuous use? If so, radiant may be worth the effort. If you are going to use this as a hobbyist, nights and weekends from a comfort and economy standpoint I would suggest the Rinnai as well. Again, I'm biased, but it is simple to install, exceedingly reliable, has a great feature set and while more expensive than the Hot Dogs will out produce them on a comfort basis.
For your 900+ sq ft you have a choice of the EX22C or the EX38C. Respectively, the differences are 8,200-21,500 vs 13,200-38,000 btu. 7 Stage modulating gas valve on each. I ran the 22 in my shop the first winter after building the shop. It heated my 940 Sq ft. really well. Last winter I put in the 38 for trial (I represented them for 20 yrs in my business and consult with them still so it was a trial unit). In the morning when I'd go out and fire the unit up and I did run it manually, it would quickly bring up the temp. However the 22 actually gave a better comfort level. Generally, folks here, and pretty much universally talk about the max input. On a single stage unit that makes sense. On modulating equipment what is more important to your comfort level is how low it will fire. In my shop the 22 gave better comfort than the 38 because the minimum fire of 8200 btu gave better comfort than the min 13,200. With the built in programmable t'stat, you could program the unit to operate as you choose.

 

[Dick in Wisconsin]

I don't know what a Hot Dawg system is. I have radiant in-floor in the 1000sf shop and LOVE IT.

BUT's are BTU's ... radiant floors put the heat where your body is .....starting at your feet. As the heat rises and cools it's less needed -- ideally the ceilings should be colder. The opposite is true with forced air -- also a huge radiant component with a head floor -- it's a big radiator.

When I first read this before I built my shop, it made sense to me.

Once I started to use my shop in the dead of winter, I realized it was true. The thermostat is on the wall of the toilet room (an inside wall) and its about five feet above the floor. I leave it at 55 most of the time. When I come in, take my coat off and hang it up, and start to work on the race cars I'm a touch cool. But after working for 15 to 30 minutes and working under the car on the creeper I am very comfortable.

The statement above about the heat starting on the floor and working up is 100% true in my book. Tools left on the floor for any length of time are warm to the touch and not cold.

My plumber knew I wanted a first class system, but wasn't above saving a few nickels and dimes where I could. He worked with the plumbing wholesaler to get my a boiler that was dented in the back for a savings of about $400 or so. Sweet!

It should be noted that I have a friend who used a 40 gallon or so propane or NG water heater to heat the fluid in his in-floor radiant system of his race shop and swears by it. A few others on the GJF use water heaters, and other condemn using them.

I have natural gas. Would do it again in a heartbeat. If I ever build a house, the attached garage will have in-floor radiant heat!