Does Radiant Floor heat make sense

[Doubled33]

A few key notes
building is for profit and not a hobby shop
16’ from slab to underside of metal deck
about 10,000 SF 70x135
4.5k sf bays with lifts, 1k sf break room/parts/ equipment storage/office 2.5k sf tool/lathe/milling area 1.5k sf storage/indoor overflow parking
building located in central MS
natural gas is at the site
building will have AC As well.

I have read a lot of posts here that discuss the amount of time needed to bring it up to temperature and the fact that it is better off to leave it running all the time which brings up the cost issue of natural gas. most of these comments come from people in habitually colder climates. The temperatures at this location very seldom get into the 20s. so I am thinking the Delta T I am trying to achieve would not be that bad as related to the natural gas cost. am I correct in this thought or is that just not how this system works?

The other question I have relates to the insulation below slab which it seems 2 inches is what is recommended. in this climate in this location, would the 2 inches still be a recommendation or would 1 inch suffice?

The slab will be around 6 to 8 inches at most locations. Does this play into the viability of radiant heat?

The exterior walls will be metal studs have at least 6 inches of insulation and the roof will also be insulated with polyiso.

how quickly does this system dissipate the heat once it is turned off. The reason I ask there are times where the temperature may be 30 in the morning and warm up to the 60s during the day. Basically, I am worried about the system, making the building too hot.

since I am planning on putting in AC, am I better off using gas heat and a ducted system?

 

[HoosierBuddy]

I have radiant heat in my garage and part of my house. Have had for over 20 years now. Put it in myself and feel qualified to answer your questions.

The only advantage of radiant floor heat in your situation (and your situation is perfect for it BTW) is comfort. It's more comfortable than forced air heat in three ways. It's essentially noise free. It's not drafty. It's even heat with no swings in temperature and basically no issues of "now I'm hot because I'm standing under the vent."

It's more expensive to install especially if you are putting in AC anyway.

We used forced air heat at work, and I would urge you to at least consider the noise issue. We are using NG hanging unit heaters (Modine Effinity) and those suckers are loud. Monday morning safety talk? You have to have someone go over and turn off the heat so the speaker can be heard. However, a ducted system running from an actual NG furnace would be significantly quieter than that.

I really like my in floor radiant, and I'd do the same thing again maybe. In your situation, where everthing has to payback? I would look hard at insulating the slab and the hell out of the walls and ceiling and going with mini splits (ductless). If you are wanting to do a major turn down on temp nights and weekends, also put in a NG heat source (unit heaters or furnace) to allow the heat to recover as the mini splits are going to **** at that.

But to answer your actual questions.

2" insulation can't be much more expensive than 1" and it's twice the R value. Why not go 2"?

Thicker floors would work even better with radiant.

I've never had a situation where my in floor radiant has overrun my temp setting due to outside temperature swings. Your winter weather is similar to our shoulder seasons in November early December, and Late March April. No issues. You will not have a problem.

Radiant would work great, and if having a super quiet system makes sense for your business.....maybe you should go that route. But, it's going to cost more and will not generate a direct payback to put those $ back into your bottom line. Also? If you have to put any tapcons into the floor in the future, or similar....remember that those heat loops are subject to damage in those types of jobs and difficult to repair.

 

[theoldwizard1]

building is for profit and not a hobby shop

For profit, meaning you are going to sell it, or are you going to run a business from it ? If you are selling the building, just go with gas forced air.

I am thinking the Delta T I am trying to achieve would not be that bad as related to the natural gas cost. am I correct in this thought or is that just not how this system works?

Recovery time has a lot to do with how cold the interior got ! Use a set back thermostat and don't go below 55°F.

The other question I have relates to the insulation below slab which it seems 2 inches is what is recommended. in this climate in this location, would the 2 inches still be a recommendation or would 1 inch suffice?

2" will slow down heat loss when the system is set back. Probably worth the investment.

The slab will be around 6 to 8 inches at most locations. Does this play into the viability of radiant heat?

Only in cool down/recovery time. You will need to "tune" the set back temperature so that it is not to cold when you come in. Or get one of those fancy thermostats that change set temp at a given time.

since I am planning on putting in AC, am I better off using gas heat and a ducted system?

This is ALWAYS the big debate ! The big win for radiant floor is COMFORT ! If your feet are warm, you are warm !

In other parts of the world, there are heat pumps that can supply cool air (with appropriate air handlers) AND hot water. I am not certain if any of those are sold in the US.

 

[Doubled33]

I have radiant heat in my garage and part of my house. Have had for over 20 years now. Put it in myself and feel qualified to answer your questions.

The only advantage of radiant floor heat in your situation (and your situation is perfect for it BTW) is comfort. It's more comfortable than forced air heat in three ways. It's essentially noise free. It's not drafty. It's even heat with no swings in temperature and basically no issues of "now I'm hot because I'm standing under the vent."

It's more expensive to install especially if you are putting in AC anyway.

We used forced air heat at work, and I would urge you to at least consider the noise issue. We are using NG hanging unit heaters (Modine Effinity) and those suckers are loud. Monday morning safety talk? You have to have someone go over and turn off the heat so the speaker can be heard. However, a ducted system running from an actual NG furnace would be significantly quieter than that.

I really like my in floor radiant, and I'd do the same thing again maybe. In your situation, where everthing has to payback? I would look hard at insulating the slab and the hell out of the walls and ceiling and going with mini splits (ductless). If you are wanting to do a major turn down on temp nights and weekends, also put in a NG heat source (unit heaters or furnace) to allow the heat to recover as the mini splits are going to **** at that.

But to answer your actual questions.

2" insulation can't be much more expensive than 1" and it's twice the R value. Why not go 2"?

Thicker floors would work even better with radiant.

I've never had a situation where my in floor radiant has overrun my temp setting due to outside temperature swings. Your winter weather is similar to our shoulder seasons in November early December, and Late March April. No issues. You will not have a problem.

Radiant would work great, and if having a super quiet system makes sense for your business.....maybe you should go that route. But, it's going to cost more and will not generate a direct payback to put those $ back into your bottom line. Also? If you have to put any tapcons into the floor in the future, or similar....remember that those heat loops are subject to damage in those types of jobs and difficult to repair.

Thanks. I should have added a few things. I had radiant in my bathroom in my CA house And yeah it was amazing. That’s what is driving this thought but this shop is 100x larger.
I forgot about the noise of those old Modine heaters as I worked under those many many years ago.
insulation such as formulae has gotten expensive and the 1” is close to half the cost of 2” at about 1.50 a sf.

 

[Doubled33]

For profit, meaning you are going to sell it, or are you going to run a business from it ? If you are selling the building, just go with gas forced air.


Recovery time has a lot to do with how cold the interior got ! Use a set back thermostat and don't go below 55°F.


2" will slow down heat loss when the system is set back. Probably worth the investment.


Only in cool down/recovery time. You will need to "tune" the set back temperature so that it is not to cold when you come in. Or get one of those fancy thermostats that change set temp at a given time.


This is ALWAYS the big debate ! The big win for radiant floor is COMFORT ! If your feet are warm, you are warm !

In other parts of the world, there are heat pumps that can supply cool air (with appropriate air handlers) AND hot water. I am not certain if any of those are sold in the US.

Do you have the name of a manufacture of the above mentioned units. A google keeps showing me heat pump residential water heaters.
I will own And run the business.

 

[Stuart in MN]

If it's a business that's occupied every day I think radiant is a good choice. Where it can fall flat for many people here on the board, is they have a home shop they'll be in a few evenings during the week and maybe on Saturday, and they want to turn off the heat other times.

 

[theoldwizard1]

Do you have the name of a manufacture of the above mentioned units.

Mitsubishi Ecodan

I'm not sure if it is sold in the US.

Edit:

Sold in the US, but uses chilled water for cooling so NO DEHUMIFICATION !

 

[theoldwizard1]

3 more

US Boiler
Arctic
SpacePak

 

[fitter30]

Mass is harder to heat than air. Mass- concrete slab and all the stuff in the building. Radiate heat in floor is the best heat. A big draw back is if there is machinery or shelving anchored to the floor there is a chance of hitting the tubing.

 

[theoldwizard1]

Trane : HVAC Basics: Heat pump + air handler matched systems

 

[Boogerman]

If you're in a warmer climate (your location would help) the average soil temperature will be high enough under a large building that the under slab insulation won't matter. I'd omit it, and put in 2 to 4 inches of foam perimeter insulation INSIDE the stem walls to at least 3, and preferably 4 feet below the slab grade. Run that all the way up to the bottom of the walls. You can put sheet metal flashing over it to protect it once you have placed the concrete floors.

As others have said, on a large commercial slab, radiant heat will be quiet, consistent, and relatively efficient. It will not overrun on warm days, and will make the building more comfortable. I think you'll find you can keep the temperature 2 or 3 degrees cooler, and still feel good.

The heat loss down into soil under a building is slow, and where the slab is large, the soil temperature rises and approaches the floor temperature, but it doesn't conduct the heat away if you have the edges insulated well. It just acts like a huge heat reservoir to even out the temprature on cold days.

I'd zone the radiant tubing, with higher density under the office/breakroom/machine shop. Low density in the parking areas and storage. That way, they will stay a few degrees cooler, and save you heating costs.

 

[manwithtools]

The heat loss down into soil under a building is slow, and where the slab is large, the soil temperature rises and approaches the floor temperature, but it doesn't conduct the heat away if you have the edges insulated well. It just acts like a huge heat reservoir to even out the temprature on cold days.

Do you happen to have any data to support this approach? I'm not disputing you and it seems logical enough, I'd just like to see some study related data. In my next shop I'd like to have radiant heat and there could be a significant cost savings if insulation was omitted.

 

[Doubled33]

If you're in a warmer climate (your location would help) the average soil temperature will be high enough under a large building that the under slab insulation won't matter. I'd omit it, and put in 2 to 4 inches of foam perimeter insulation INSIDE the stem walls to at least 3, and preferably 4 feet below the slab grade. Run that all the way up to the bottom of the walls. You can put sheet metal flashing over it to protect it once you have placed the concrete floors.

As others have said, on a large commercial slab, radiant heat will be quiet, consistent, and relatively efficient. It will not overrun on warm days, and will make the building more comfortable. I think you'll find you can keep the temperature 2 or 3 degrees cooler, and still feel good.

The heat loss down into soil under a building is slow, and where the slab is large, the soil temperature rises and approaches the floor temperature, but it doesn't conduct the heat away if you have the edges insulated well. It just acts like a huge heat reservoir to even out the temprature on cold days.

I'd zone the radiant tubing, with higher density under the office/breakroom/machine shop. Low density in the parking areas and storage. That way, they will stay a few degrees cooler, and save you heating costs.

Central MS. Was noted in post 1 albeit easily missed.

Your comments mirror my thoughts on already having a warmer ground and no freezing ground in the area thus the question.

Thanks for your insight.

 

[Doubled33]

Mass is harder to heat than air. Mass- concrete slab and all the stuff in the building. Radiate heat in floor is the best heat. A big draw back is if there is machinery or shelving anchored to the floor there is a chance of hitting the tubing.

Yeah I can block out clear space for what I know now but if things get moved in the future perhaps it anchors to a pad or I have to be careful of loop location.

Don’t want to jack hammer every time to fix a loop.

 

[PoorUB]

If running floor heat you can run the heat in the building 5-10 degrees colder and still be comfortable. We ran the room temp on a sheet metal shop at 65F and the guys would work in t-shirts. If overheard doors are open it recovers extremely fast. You don't have drafts from forced air or the noise. Costs more to install, and probably a bit more to operate, but the comfort issues make it very popular.

 

[dscheidt]

Yeah I can block out clear space for what I know now but if things get moved in the future perhaps it anchors to a pad or I have to be careful of loop location.

Don’t want to jack hammer every time to fix a loop.

Set the loops low, an inch or so off the bottom. Very little requires anchors more than 2” into a slab, so even in a 4" slab, as long as the person drillling the holes isn’t an idiot, anchors can go wherever you want them.

You haven’t provided your location well enough to know what your climate zone is, but much of MS is climate zone 3, where the IECC requires R10 under slab insulation, at least for the edges. The material cost of going from 1" foam to 2 is double, but the installed cost isn't, because the labor to do the insulation is the same. Remember that insulation keeps heat out, as well as in, so you benefit from proper insulation and air sealing in the summer as well.

The big win with radiant heating is comfort. The temperature is uniform throughout the space, and it recovers quickly from having a door open to move a vehicle in or out. There are also no blasts of hot (or only sort of warm) air, and it's dead quiet.

 

[theoldwizard1]

If you're in a warmer climate (your location would help) the average soil temperature will be high enough under a large building that the under slab insulation won't matter. I'd omit it ...

If you do, you absolutely must put down a vapor barrier !

 

[larry_g]

A few key notes
building is for profit and not a hobby shop
16’ from slab to underside of metal deck
about 10,000 SF 70x135
4.5k sf bays with lifts, 1k sf break room/parts/ equipment storage/office 2.5k sf tool/lathe/milling area 1.5k sf storage/indoor overflow parking
building located in central MS
natural gas is at the site
building will have AC As well.

Precision machines like highlighted in red above will keep there calibration and work better if maintained at a constant temp which floorheat provides. It is also much more comfortable for the people who have to work on it. I don't know the accuracy that you intend to produce with your machines but if you are temp cycling them they will move and accuracy goes out the window. I have worked in two different shops as well as my own and can say that floor heat is the best. Like someone said above you can keep the ambient temp much lower and still have a pleasant temp to work in.

lg
no neat sig line

 

[Doubled33]

Set the loops low, an inch or so off the bottom. Very little requires anchors more than 2” into a slab, so even in a 4" slab, as long as the person drillling the holes isn’t an idiot, anchors can go wherever you want them.

You haven’t provided your location well enough to know what your climate zone is, but much of MS is climate zone 3, where the IECC requires R10 under slab insulation, at least for the edges. The material cost of going from 1" foam to 2 is double, but the installed cost isn't, because the labor to do the insulation is the same. Remember that insulation keeps heat out, as well as in, so you benefit from proper insulation and air sealing in the summer as well.

The big win with radiant heating is comfort. The temperature is uniform throughout the space, and it recovers quickly from having a door open to move a vehicle in or out. There are also no blasts of hot (or only sort of warm) air, and it's dead quiet.

I looked and am in zone 3. I have an arch on board and we are working to onboard the Mechanical Engineer. Trying to decide if I want this system or not as the building owner.

If tubes are at the bottom and that still works then I would like to peruse that design. Most of the reading did shows at the top but if heating the mass I would think location my not matter that much.

Looks like 2” of foamular gives me the R-10.
I played the game of average and minimum R values in CA with title 24 over the years. Mostly came into play at roof drains and such areas. Looks you are noting above that perimeter insulation may satisfy in lieu of whole under slab.

I am a heavy commercial GC but never built in a cold climate and never did a Radiant system.

Thanks for the input.