How efficient is in-floor heat?

[cfk]

Building a 40x48 shop and haven't decided how I'm going to heat it yet.. I want the shop heated all the time, but only need it "working temps" maybe an evening to two a week.

I have heard about guys that heat the concrete to 45, and then use a standing hanging unit to bring it up to 65 when they want to work in there, so the question is: How much more efficient is in-floor heat at keeping the building at 45 degrees than a standard heater? If I figure it would cost me $7k to install the in-floor heat, would that ever pay off?

This is in southern Iowa, climate zone 5.

My gut tells me it would never pay for itself, but I'd like to hear some opinions.

 

[yeldogt]

You don't save money doing radiant ...... Installing or running. BTU's are BTU's ..... the only savings you get with radiant is the possible lower overall temp required to be comfortable. This can be greater in larger spaces with very high ceilings as there is less waste heat high up.

Slab radiant is also very slow to respond -- trying to bump up a temp twice a week is most likely not all that great an idea. The key with any building is the insulation .. tight well insulated buildings will be less expensive to maintain.

Do you have natural gas? ... properly insulated -- that will not be expensive to keep a nice temp 24/7.

You need slab insulation with radiant

 

[HoosierBuddy]

Agree 100% with yeldogt. The reason we do radiant is the comfort.

If you're looking at lowest operating costs, and have natural gas available, I'd highly recommend the Modine Effinity line of high efficiency hanging heaters. They are quite a bit more up front then the standard Modine heaters but the increased efficiency will generate payback. We have 3 of them at work (put in one per year for 3 years...with the oldest about 10 years old now)...and have been problem free. They vent with PVC rather than a B-vent which is a plus in my book. However, as they are fully condensing, you do have to have a condensate drain.

Anyway....the only thing I don't like about these units is they are pretty loud and blow a lot of air around. Radiant doesn't do that and is almost silent....but it's more expensive to install and not any cheaper to operate if the equipment efficiencies are about the same.

Phil

 

[Duke74]

In floor heat is good for drying up water that’s on your floor. The problem with
It is regulating your air temperature with it. If your thermostat is wall mounted, by the time the slab warms up enough to make the stat turn off, it is hot enough that it will keep warming up the air and makes it too hot. You are better off going with a stat operated by a temperature probe in the floor itself. I would still go with radiant tho. My brother heats his whole house with in floor heat and he complains all the time, he wishes he had a forced air system.

 

[Duke74]

To answer your question though, I would think it is efficient due to the fact that the slab holds the heat so well. Just my 2 cents worth.

 

[Copymutt]

25 yrs. w/ exactly the combo you’re thinking about. Never looked back. NG makes the most economical choice. I keep it at 50*, turn on the Modine when I’m out there and very comfortable in a few minutes. Did have to replace the Grundfos pump cartridge once. That’s been it. Zone 5. Well insulated slab w/ thermal break between slab & stem wall.

 

[Rc_Guy]

Didn't he say he would bump it up with a hanging furnace?

 

[theoldwizard1]

You don't save money doing radiant ...... Installing or running. BTU's are BTU's ..... the only savings you get with radiant is the possible lower overall temp required to be comfortable. This can be greater in larger spaces with very high ceilings as there is less waste heat high up.

Slab radiant is also very slow to respond -- trying to bump up a temp twice a week is most likely not all that great an idea. The key with any building is the insulation .. tight well insulated buildings will be less expensive to maintain.

Spot on !

Radiant heat is the most COMFORTABLE form of heat ! If your feet are warm, you feel warm. The opposite it true also.

If a large percentage of your space is storage, don't spend the extra to do radiant in-floor heating, at least in those areas. Not sold in the US, but in some areas of the world you can get mini-split heat pumps that have a heat exchanger for radiant heat as one 9f the outputs.

If the are looking to improve the thermal efficiency of you project, vapor barrier and ≥ 2" of rigid insulation in the floor will make a difference.

 

[cfk]

Awesome, that is exactly the information I was looking for. I was under the impression that keeping my building at 45 degrees with in-floor heat would be cheaper than keeping it at 45 with a hanging heater, so thank you guys for clearing that up.

Few follow-up points and questions..

I do not have natural gas, all propane. It was going to be $12k+ to hook up NG, which made the decision to go with geothermal in my house even easier, so now I'm definitely propane only.

I am contemplating insulating the slab - figured it would cost me about $2k, and will maybe help to keep the slab a little warmer (?) and hopefully lower the heating cost a little. If I go ahead and do that, I might as well spend the couple hundred more bucks and at least run the water lines for radiant - just in case I ever want to hook it up in the future.

 

[cfk]

You are better off going with a stat operated by a temperature probe in the floor itself.

And I suppose its even more of an issue with a hanging heater as well (except the opposite problem). If I turn the heat up to 65 with the hanging heater on a Saturday morning and then spend the day in there, the slab never thinks it has to run and will take a while to recover once the hanging heater is off and the air temp is cooled back to 45..

or not really?

I would still go with radiant tho. My brother heats his whole house with in floor heat and he complains all the time, he wishes he had a forced air system.

I'm confused.. those two sentences are contradictory.

 

[Jackfre]

You have geo in the house. If you have the capacity in your geo source just extend it to the shop and use a water to water heat pump for your slab. There are many out there. Also, as you are planning and have some time, also look into the newer air to water heat pumps. John Siegenthaler, the main man in radiant, did a column on them a month or so ago. Radiant with a heat pump is excellent as it is low temp. I suspect that either option will be better than an LP boiler. Cost is probably a push but operating cost will be less. For your secondary I would look at a Rinnai EX38 in propane. Not cheap but nothing in the category is better. I have one in my shop and from 10’ away you can barely hear it.

 

[Duke74]

The air temperature from the forced air will warm the slab up somewhat, but the temperature probe in the slab is fairly deep so it should still respond with the temperature of the slab. I was not trying to be contradictory in my post. What I meant was IF you go with slab heat it is best if you have the sensor in the slab. I didn’t mean it was better than forced air. Anyways I will say I am not a heating guy. I am an electrician that works around heating so I am just passing on what I see.

 

[cfk]

I was not trying to be contradictory in my post. What I meant was IF you go with slab heat it is best if you have the sensor in the slab.

I got ya now!

I was just confused when you said you would go with radiant but your brother has it and hates it.

You have geo in the house. If you have the capacity in your geo source just extend it to the shop and use a water to water heat pump for your slab.

I doubt I have the capacity in my system for that (closed loop), but I'd have to ask my hvac guy about that. I know they used to put geo systems in slab homes with radiant heat a few years ago, but it doesnt seem like people were real impressed with them and my hvac guy says he doesnt install them any more, but I don't know any more details than that.

 

[larry_g]

Talk of comfort from above. My old shop had radiant tubes in the floor and hooked to a water heater for a heat source. In the cold of winter the floor was 60-65* and the ambient temp would be a bit lower. However I could work comfortably. My feet were warm and with a sweatshirt I was comfortable. The big advantage my tools were warm to the touch. The mill and lathe did not feel cold and hurt to touch. I could lay on the floor working under equipment and still be warm. The warm floor makes a different working environment than a place with forced air heat that leaves the floor cold and the big iron tools cold for a long time. It really is great heat for a shop where your doing physical work, warm feet and a cool air.

lg
no neat sig line

 

[65ranchero]

I have a 26x30 (780sf) 2 bay garage one high bay for the lift and the other bay 9ft ceiling
2x6 construction, over a 4ft high poured concrete stem walls on 3 sides.
Sheathed in Advantech and added Tyvek VB and vinyl sided.
Stem wall has Insofast attached and then covered with FRP.
Floor has 2inch ridged foam board then covered with 4 to 6" of concrete
before pouring the floor 4 different loops of PEX hooked up to a manifolds and the hooked up to my house hot water oil burner on a separate circulating pump.
Thermostat on the wall is set at 58F all winter and keeps the floor and shop warm if not more that what it is set for by a couple of degrees.
it is comfortable to work in and I really do not do not notice a big drain on the oil budget.
So I say set it and forget it.

 

[jack stand]

If you have tall ceilings, radiant is the only way to go. I went from a shop (in MD) with LP ceiling hung heaters to my shop in Maine with radiant.
Both have 16' ceilings. With the LP the hot air rose up against the ceiling and my fans blowing it back down made for a cold draft feeling with the tstats set at a "reasonable" shop temp of around 60*. I'm not sure that even set at 75 or so wouldn't still feel like a cold draft. And forget opening a door and bringing in a vehicle, let alone a 30* or less vehicle.
Now with the radiant with the same setting, none of these problems happen. Opening a 12x14 door is a casual event that is over and unnoticeable once the door is closed. Cold frozen vehicles, pfft a non issue. If this shop is your final landing place do the radiant, set it and forget it and enjoy the comfort
To be fair, the MD (LP) slab was not insulated but was almost half the size.
With one of the combinations you mentioned about installing radiant with ceiling hung LP air heaters, I'd wonder about payback on the Modines savings by running the radiant at a lower "maintenance" setting and bumping up occasionally with the modine type heaters.

 

[Showkey]

Dont think “heating the slab to 45*“ is the answer.

Heating the slab to 70*-80* with 100-120* water and heating the room to 50* might work.

 

[Rc_Guy]

Dont think “heating the slab to 45*“ is the answer.

Heating the slab to 70*-80* with 100-120* water and heating the room to 50* might work.

Why wouldn’t heating the slab to 45° work?

 

[Showkey]

Because my slab in my unheated attached garage is 45* most of the winter with no heat.
Even when it -25* outside the slab never freezes. So yes……no money spent.

So when you want the garage to be 60* the 20,000 pound slab needs to warm up to 80* to get the air to 60* which is going to take a long time………?

A good friend had a radiant similar system……his heating guy said set the thermostat on the wall at 60* let the system heat the building and pay the bill. Don’t know the details of the conversation……but..it was centered around saving money on heat with radiant in floor system.

 

[cfk]

With one of the combinations you mentioned about installing radiant with ceiling hung LP air heaters, I'd wonder about payback on the Modines savings by running the radiant at a lower "maintenance" setting and bumping up occasionally with the modine type heaters.

My original thought was that heating the slab was more efficient, so if I wanted to keep the building at 45 degrees 24/7, doing that with radiant would be the cheapest way to do it (the original question that prompted this thread). But because the radiant is very slow to change temps, I would use a hanging heater to bring the building temp up to 65 when I wanted to work in there for an evening or something and then shut it off.

If radiant is my only heat source, I would have to keep the shop at 55 all the time which seems like it would be a waste if I'm not out there all the time, why is why I figured keeping it at 45 and then bumping it up when I needed seemed logical.

I was basically looking for the most cost effective option (I'm fine with paying more up front if it pays for itself down the road) between these options:

1) Hanging heater only; keep the building 45 all the time, bump it up to 65 when I want to work.
2) Radiant heat keeping the shop at 45, hanging heater to get to 65 on occasion.
3) Radiant heat all the time, keep it at 55.

And forgot to mention - 14' ceilings..

 

[Jackfre]

I got ya now!

I was just confused when you said you would go with radiant but your brother has it and hates it.



I doubt I have the capacity in my system for that (closed loop), but I'd have to ask my hvac guy about that. I know they used to put geo systems in slab homes with radiant heat a few years ago, but it doesnt seem like people were real impressed with them and my hvac guy says he doesnt install them any more, but I don't know any more details than that.

Do your own research prior to speaking with your guy.

 

[sixty4]

I have a 30x40 20' high detached garage I put the blanket down and tubing in as it was cheap. I started thinking about it if it's Hot water I need to leave it on almost all winter. I ended up doing a Hot air furnace with ac. I have a nest t stat so turn either heat or air on before I head over.

 

[PoorUB]

Why wouldn’t heating the slab to 45° work?

If you want room temp around 45F you will need to run the floor much warmer than that, maybe 10-20 degrees warmer. It depends on the heat loss of the building. A 45F slab will get you a room temp of 25-35 degrees.

If you are going to be working in the shop often radiant floor is a no brainer, just do it! If occasional use, then you can suffer with a cold slab.

 

[Rc_Guy]

If you want room temp around 45F you will need to run the floor much warmer than that, maybe 10-20 degrees warmer. It depends on the heat loss of the building. A 45F slab will get you a room temp of 25-35 degrees.

If you are going to be working in the shop often radiant floor is a no brainer, just do it! If occasional use, then you can suffer with a cold slab.

I live in a pole barn house, in floor heat in the house in floor heat in the garage, all winter long my garage is at 68° if I use my infrared heat gun the floor is at anywhere from 65° to 70°

 

[yeldogt]

Didn't he say he would bump it up with a hanging furnace?

He did .... the question is how often will he be bumping up and with what? The key is insulation and air sealing -- get that building reasonably efficient within reason economically. If you do that and get the proper equipment -- heating and maintaining 1900sf can be done at a reasonable cost. Some people don't mind working in colder spaces ... 45 is cold .... with radiant that's going to need antifreeze. I worry at low temps like that with radiant. Also --- how fast do you want to raise the temp ? With radiant you need more (tighter) spacing to get more heat to the slab. With a hanging you have to determine how big ,,,, and what's the efficiency and cost. What's the point of a typical 80% furnace to raise the temp ... when you can have a 98 boiler keeping it warm. What's the payback ?

With the right boiler and tight enough pex spacing it can work very well and be efficient. That said -- I do drop down my studio spaces when I'm going to be gone for a couple weeks. Previoulsy I had a 220v electric heater in my one studio (winter weekend house) --- normally I would arrive in the evening and just turn the system up a bit and it was ready the next morning. If I arrived and wanted to work the electric heater would quickly heat the area I normally went to. Now I do internet control ....

 

[yeldogt]

My average return water temps are in the 7 degree range higher than my desired room temp w/ mixed radiant types in a house setting when shooting for 72 degrees. .... lower when only a slab. Once you get them at temp they are stable.

More tubing in the slab makes the difference less w/ faster response time. Thicker slab is going to respond slower.

With the OP using Propane he may want to look into a mini-split heat pump ... the best way to control any radiant system is using outdoor reset .... this way you can plug in any target temp and the system will adjust automatically. You can set the system for 60 and use the heat pump. Properly located a single point source can be used to warm an area where you will be working .....most people don't use a workspace fully. You tend to be doing things in a given area.

Again -- spend the money on insulation and you get a more confortable space and lower running costs regardless of heat source.

In NY I had a very nice space --- well insulated. I used a propane fired sealed combustion cabinet heater -- like them over the ceiling. Quiet and they put the heat along the floor where you want it

 

[Shop Specialties]

With in-floor you set the temp and leave it. Do not go up/down and all around like you would with forced air. The in-floor when designed and installed properly can take up to 1/3 of the BTU to heat the same size area as compared to forced air. I have been doing nothing but heating for 30 years here in Montana and every single one of my customers with in-floor use less fuel than my forced air ones. A great example would be a customer of mine in Eastern Montana. They have 2 shops right across the street from each other. The one with in-floor is at least 2,000 sq, foot larger and they have snow melt. They set the thermostat at 70* and leave it since they an abundance of free fuel and that shop uses less fuel than the smaller shop with forced air.
If you want to have 1 constant temp all Winter and save fuel go in-floor. If you want the wind blowing in the shop and want to dilly dally around with the thermostat all the time to save fuel then go forced air.

 

[yeldogt]

With in-floor you set the temp and leave it. Do not go up/down and all around like you would with forced air. The in-floor when designed and installed properly can take up to 1/3 of the BTU to heat the same size area as compared to forced air. I have been doing nothing but heating for 30 years here in Montana and every single one of my customers with in-floor use less fuel than my forced air ones. A great example would be a customer of mine in Eastern Montana. They have 2 shops right across the street from each other. The one with in-floor is at least 2,000 sq, foot larger and they have snow melt. They set the thermostat at 70* and leave it since they an abundance of free fuel and that shop uses less fuel than the smaller shop with forced air.
If you want to have 1 constant temp all Winter and save fuel go in-floor. If you want the wind blowing in the shop and want to dilly dally around with the thermostat all the time to save fuel then go forced air.

With a shop -- my guess is with a commercial shop yes there would be savings. When we had our plant in DE -- the loading zone was heated w/ radiant. And the door was open more than closed. Heating that with forced air would have been crazy.

In a closed setting like a house or typical hobby type space --- there is not much

 

[65ranchero]

if I use my infrared heat gun the floor is at anywhere from 65° to 70°

Same here! set it and forget it as others have said

 

[HPRifleman]

With in-floor you set the temp and leave it. Do not go up/down and all around like you would with forced air. The in-floor when designed and installed properly can take up to 1/3 of the BTU to heat the same size area as compared to forced air. I have been doing nothing but heating for 30 years here in Montana and every single one of my customers with in-floor use less fuel than my forced air ones. A great example would be a customer of mine in Eastern Montana. They have 2 shops right across the street from each other. The one with in-floor is at least 2,000 sq, foot larger and they have snow melt. They set the thermostat at 70* and leave it since they an abundance of free fuel and that shop uses less fuel than the smaller shop with forced air.
If you want to have 1 constant temp all Winter and save fuel go in-floor. If you want the wind blowing in the shop and want to dilly dally around with the thermostat all the time to save fuel then go forced air.

How long do you leave it? During the normal heating months (October-April) or all year round?

 

[65ranchero]

Normal heating months.
turned off at the thermostat.
I could probably just leave the T stat on because ambient should keep it off but I don't, if it gets too cold in the garage at that late in the season I just open the doors it's warmer than inside!

 

[Shop Specialties]

How long do you leave it? During the normal heating months (October-April) or all year round?

Just during your normal heating months. With it being 100* out right now the guys in the shop would probably get a lil pissed off at me if I told them they had to leave the heat on.

 

[jack stand]

If radiant is my only heat source, I would have to keep the shop at 55 all the time which seems like it would be a waste if I'm not out there all the time, why is why I figured keeping it at 45 and then bumping it up when I needed seemed logical.

I was basically looking for the most cost effective option

CFk I would expect that if you put your LP heating costs into upgrading your insulation and air sealing values that keeping your shop and everything you have in it nice and toasty 27/7 very economically.
This holds true for any heat type. The less heat leaving (or entering) your building, the less the heating/cooling source really matters.
I've learned this first hand on my last several builds. I'm not in the HVAC business or educated in this and it took me a while to learn that your biggest concern and consideration must be your overall insulation "package". The better insulation is, the LESS how you get it there matters.
FWIW I heat my (attached) house and 40x64x16'6" shop with under 6 cords of wood annually. Someone else here might convert those BTU's to gallons of propane, #2 oil or KW. for some comparison.
This is my first radiant heat and it's very difficult to describe how different it is from "warm air", but it really is not comparable. Hard cold concrete is a miserable enemy in the winter regardless of the air temperature.
Radiant is damn near magic in terms of comfort.

 

[yeldogt]

People make the mistake going in with a new space not planning to maintain temp ..... they view the shop like the house. For most people the shop is not going to be as warm as a house and the shop is not going to have the windows and other items that make a space harder to condition. Spend the small up-charge to properly insulate -- get a better door. The payoff is a lifetime of savings.

One of my spaces is an upgraded ....not new build space. It's 1600sf and it can be heated with a 4000kw electric heater making around 13k BTU. I know because I had to do it while the property was being rebuilt and the propane services upgraded ... The heater now is a 40k 80% propane and I keep in the lower 60's ... I turn it up a few degrees when I'm there. I'm going to be doing another space about the same at my new place ...have not decided on the type of heat

 

[Ak Jim]

If you want room temp around 45F you will need to run the floor much warmer than that, maybe 10-20 degrees warmer. It depends on the heat loss of the building. A 45F slab will get you a room temp of 25-35 degrees.

If you are going to be working in the shop often radiant floor is a no brainer, just do it! If occasional use, then you can suffer with a cold slab.

This is completely untrue. I live in interior Alaska. I keep the garage set to 67. When it’s -50 outside the floor temp is 72. Now if the building has no insulation then maybe your numbers are correct.

 

[Rc_Guy]

This is completely untrue. I live in interior Alaska. I keep the garage set to 67. When it’s -50 outside the floor temp is 72. Now if the building has no insulation then maybe your numbers are correct.

That is what I said here last week, I'm in Minnesota in a pole barn house, garage is at 67° all winter and floor is 68°-70°

 

[finn]

I added a hanging heater to my radiant floor heated shop. I maintain around 42-45 degrees and bump the temp to about 60-62 degrees, sometimes 65, when I’m working. From memory, the slab is about 54-56 degrees.

Works for me, and greatly cuts down on propane use. The building heated area is a 32x75’ work area plus a 16x16’ office/ bathroom area.

It has three man doors, two 14’ high garage doors, and five large windows, along with 16’ ceilings, lots ao leak paths to contend with, and lots of volume to heat.

Much of the early advice in this thread I factually and scientifically correct and consistent with my experience. Some of the later advice is anecdotal and conjecture. Lots of fan boy stuff filtering in.

A warm floor is, for most people, comfortable to work on, but, in itself, doesn’t save energy. Insulation of a tight building saves energy. Minimizing heat loss is where the savings comes in, and low delta T between your heated area and the outside environment is what counts, ie low thermostat set points, along with good floor and slab perimeter insulation.

The hanging heater is a relatively cheap way to allow a low thermostat set point and fast warm up of a building that isn’t used every day. The hanging heater compensates for the inherently poor response rates of the floor heat system. My Beacon Morris 75k was probably $400 plus venting, a breaker, 15’ of wire, 15’ of black pipe, and the venting.... probably $1k Max.

 

[rsanter]

Look up “the half plan” on the Internet.
Engineer guy wanted to cut his utility costs in half and had radiant heating system so he built solar collector/solar heating system.
Large box with black tubing in it, built onto the side of a shed facing the primary sun direction.
He was in show country so the angle was to shed the show. He bolt a solar collecting box painted black inside with black piping. Idea was to have the sun heat the water in the tubes part of the way and then let the furnace heat it the rest of the way as needed for the radiant system. For your system you likly only need the solar part of it and then add the space heating to bring the temp up for when you are working

 

[Showkey]

I added a hanging heater to my radiant floor heated shop. I maintain around 42-45 degrees and bump the temp to about 60-62 degrees, sometimes 65, when I’m working. From memory, the slab is about 54-56 degrees.

Works for me, and greatly cuts down on propane use. The building heated area is a 32x75’ work area plus a 16x16’ office/ bathroom area.

It has three man doors, two 14’ high garage doors, and five large windows, along with 16’ ceilings, lots ao leak paths to contend with, and lots of volume to heat.

Much of the early advice in this thread I factually and scientifically correct and consistent with my experience. Some of the later advice is anecdotal and conjecture. Lots of fan boy stuff filtering in.

A warm floor is, for most people, comfortable to work on, but, in itself, doesn’t save energy. Insulation of a tight building saves energy. Minimizing heat loss is where the savings comes in, and low delta T between your heated area and the outside environment is what counts, ie low thermostat set points, along with good floor and slab perimeter insulation.

The hanging heater is a relatively cheap way to allow a low thermostat set point and fast warm up of a building that isn’t used every day. The hanging heater compensates for the inherently poor response rates of the floor heat system. My Beacon Morris 75k was probably $400 plus venting, a breaker, 15’ of wire, 15’ of black pipe, and the venting.... probably $1k Max.

Don’t know the answer………but………the question is: if your system was just the hanging Beacon Morris* would the heating cost and heating effectiveness change for better or worse, knowing what you know would you spend the extra cost for in floor radiant ?

* given a larger btu unit 150k for the building size and climate

 

[cfk]

Don’t know the answer………but………the question is: if your system was just the hanging Beacon Morris* would the heating cost and heating effectiveness change for better or worse, knowing what you know would you spend the extra cost for in floor radiant ?

That's my question as well.