New Garage Radiant Floor Heat system only getting air temp up to 55F

Ojigwan

I have just finished installation of a slab on grade floor heat system for a garage / workshop (roughly 6" slab). We put in a closed system with 5 loops of 300 ft of 7/8" PEX tubing. The building is a steel building, 50' x 35' (WxL) 14' high on the sides and 22' high in the center. It is an unfinished concrete floor. This is my first floor heat system and so I worked with a supply/design company to help design the system and determine the boiler, feet of tubing, tubing diameter etc., but we did the installation, wiring and concrete work ourselves. We went with an electric boiler rated at 68k BTU. I filled the system with propylene glycol, but have struggled to find out what the exact mixture should be, as it has been extremely cold lately we have probably too high a glycol to water mixture. Our shop is in Virginia and we hope to keep it at around 65-70F so we can do fiberglass work year round.
Under our slab we have 2" green board insulation and a vapor barrier. We are in the process of insulating the building with a radiant barrier/reflective foil closed-cell polyethylene foam.
I have been running the system non stop for 3 days and the slab has come up from 34F to around 60-70F, but the air is still only 55. The inlet water temp is around 115-120F and the return water temp is around 80F. When I ordered the system I indicated the building dimensions and at that time we weren't planning on insulating the shop. The company recommend the 68k BTU electric boiler and the tube layout. At this point I am worried that we don't have enough BTUs to properly heat the shop. It is quite cold at the moment (15-20F at night and around 32F during the day. I am planning on thinning the glycol mix and making sure there is no air in the system again this weekend, but I am worried that the system just isn't enough for our shop. Any ideas or thoughts are greatly appreciated. We considered using tap water only, but with the recent temps we were worried that the slab was too cold. The boiler is a 240v, 80 amp unit. My concern is that it has been running non stop for 3 days and doesn't seem to have gotten the building up to our needed temp. In some areas (right by the manifold) the slab is quite warm, but further away it cools down to close to 50-55F.
I would appreciate any advice or thoughts on what we may have done wrong or can do to remedy this problem or at least get more efficiency from our system.
Thanks,

rick in Alaska

If I am reading this correctly, you have no insulation in the outside walls. If that is the case, then I can see no way you would ever get the shop temperature up at those outside temps. You would be losing way too much heat through the building. You definitely have to have insulation in the walls/ceiling to make this work.
Also, I am not sure, but it might take a little bit longer to get this much slab up to temperature, so maybe in a couple more days it will start to stabilize.
Rick

Zman

You cannot heat the great outdoors with a radiant slab. What are the specs for the insulation?

hot_rod

And just wait until you get the electric bill for running the boiler non stop

What is or will be the final building insulation walls and ceiling? Insulated over head garage door?

It sounds like the load calc is correct, 1750 square feet? 5 loops of 300 probably has your tube spacing a bit wider then 12"on center?

35-40% glycol should be sufficient, it varies a bit from brand to brand.

Sounds like you need to tighten up the structure more.

With out any building insulation you are running more of a covered snowmelt slab.

HomerJSmith

Get a cheap glycol refractometer and check your anti-freeze concentration. Yes, 35 to 40% is probably adequate in an insulated building. But why are you using glycol? Worried about power failures?

Are your circulators sized properly? You lose 12-15% of your head energy with a glycol mixture. Do you have flow indicators on your manifold? What was your designed flow? What is your tube layout--loop--serpentine? Insulate the building envelop and report back.

ratio

Is the return temp still coming up, or has it stopped climbing? If it's still climbing you're still charging the slab. I have a radiant floor, roughly 63 x 78 x 6"+, poured in the late 50's so no insulation that I'm aware of, it takes about a week to warm up & cool off. At least, that's how long it takes to start getting complaints if the boiler locks out!

Jamie Hall

Patience, patience! And get some insulation in there.

Ironman

I certainly agree about tightening up the building. Is there any insulation around the EDGE of the slab?

What model/size pump do you have?

35% glycol should be sufficient for almost anywhere in Va except the western highlands.

A 68k btu boiler should be sufficient, but your numbers don't add up: a 68k btu boiler is 20kw; that would require a 110 amp circuit, not an 80 amp.

Where in Va are you? I'm near Staunton.

Ojigwan

Thanks for all the great feedback.
I have just ordered a glycol refractometer, I will update when I get the results.
The glycol I purchased is
"Non-toxic virgin propylene glycol formula. 30% virgin glycol for burst protection in copper pipes to -60°F (-51°C) Added inhibitors prevent corrosion in engine components and seals including aluminum, brass, copper and solder, Ready to use—does not need to be diluted". Do I dilute this further, or fill the whole system? My initial fill was with the solution as is and then I added additional water to bleed the system, at this point I believe I have around 25% water and 75% of the pre mixed glycol. I will check it tomorrow. This product is sold as a winterizer for boats, but I called the manufacture of the product and the boiler manufacture and they said it should work fine. I have a wholesale account so this was much much cheaper than I could find it elsewhere. I feel like perhaps this was not a good idea.

We went with glycol as I was worried about losing power and having the water freeze, how worried should I be, with the cost and investment in the system I thought it was a good preventive measure, but I would appreciate advice from those with more experience. Only a few times in the last decade have we lost power for more than 24 hours, but with the cost of the system I thought it was worth the peace of mind.
We have finished insulating the building. Ceiling and walls (except front wall as we are in process of building a large 24'x12' bi fold door and plan to insulate once it is complete.
Prodex Total Fast Action Insulation: R-value 16 is what we have on the walls and ceiling.
Under the slab we used R10 Unfaced Polystyrene Foam Board Insulation. We have not put it on the exposed slab outside, I am guessing we should do that, any recommendations on how we can stick the foam to the concrete, I am sure that will help, as it is above the ground I wasn't sure how best to insulate it?
Our location is in King George county near the Potomac river.
We actually have 2 60 amp 240v breakers for the boiler and a separate circuit for the 110v pump feed line (20 amps I think).
Correct on the amps, I had an old spec sheet that said 80 amps, but when it arrived it needed to be wired with the (2) 60 amp breakers.
The pump is an alpha Grundfos: I don't have the specs on it, but will tonight when I am back at the shed. It came as part of a radiant ready system and was spec'd for the system. Thanks for all your observations and responses, they are very helpful.

Ojigwan

This is the rough tubing outline. We followed it as best we could.

Ojigwan

This is the pump.

hot_rod

Ideally you want to use a glycol blended for hydronic or solar system as it will have important inhibitors blended in.

Know too, that there are two temperatures with glycol, one is freeze point where the fluid will slush and not circulate, but will not freeze solid. Often a 30% will be around 0 degrees freeze. Then the burst temperature is where the fluid will freeze sold.

Your 25% really the freeze temperature is what you look at. It may have a freeze point above 0, and a bust around -40. That should be adequate to protect in your area. But read the data from the fluid manufacturer to be sure.

Also hydronic glycols don't usually blend below 30% as the inhibitor package becomes too weak. According the Dow anyways.

The same conditions that are causing your slow ramp up will also protect you for several days in a power outage, the mass of the concrete. Your slab at 6" depth could be 16 yards of concrete or around 64,000 lbs of flywheel!

If the tube is at the very bottom of the pour, that increases ramp up temperatures also.

Gman66

Something is not hanging together for me. For 68K BTU and delta T of 35 degrees you get estimated flow of only 3.88 gal/min w/ water. Fudge for glycol and you have less than 4.5 gal/min which seems way to low for 5 x 5/8" loops (what is 7/8" pex anyways?). Estimated flow is that much lower than expected if 3/4" or 1" pex.

Are some of the loops closed? What temp is the boiler set at? Is the boiler reaching temp and cycling? Is the circulator set on high?

From the picture above the copper near boiler piping looks remarkably small but that could be the result of perspective.

leonz

You don't want to thin the glycol if anything you want more glycol.
Have the heating loops been purged of air?
Where is the expansion tank and air scoop?

In car wash boilers the boilers for the heated floor systems have 100% automotive antifreeze with an expansion tank to match the system total volume. The floors in the car wash bays are heated to a high temperature to melt ice and snow. They are also run around the clock with no set backs in the late fall to later in the spring annually.

If your not going to insulate the building which would keep the cold in as is it would be simpler and more cost effective to install the smallest AHS coal coal gun boiler being the S130
with 130,000 BTU gross output and set it at summer operating temperatures of 140 low 160 high with a high limit dump temperature of 190 and a differential of 10 degrees.

You could keep the glycol system or use straight water and just be sure that the coal stoker boiler is plumbed properly per AHS the instructions in the owners manual and the local and national plumbing codes.

In the event of a power outage an AHS coal gun boiler will stop
running and hold the fire for many hours

You will save money and be warmer as the slab will stay at a more uniform temperature longer without set backs which would cause any system to run more.

You have a high volume of air space in the building too with no insulation and a thick slab.
I do not think they being the boiler reseller did you any favors in my opinion.

An AHS S130 coal stoker will work well but it cannot placed be anywhere near where you are storing or spraying combustable liquids.

Ironman

It looks like the pump is on a 3/4" copper line, correct? If so, you're only gonna move about 4 gpm. With a 68k btu boiler input, that translates to a 34* delta T like you're seeing. The common piping should be 1 1/4" to get the flow you need.

Can you post some pics of the boiler, pumps, near piping, manifold, etc.?

hot_rod

leonz said:

You don't want to thin the glycol if anything you want more glycol.
Have the heating loops been purged of air?
Where is the expansion tank and air scoop?

In car wash boilers the boilers for the heated floor systems have 100% automotive antifreeze with an expansion tank to match the system total volume. The floors in the car wash bays are heated to a high temperature to melt ice and snow. They are also run around the clock with no set backs in the late fall to later in the spring annually.

If your not going to insulate the building which would keep the cold in as is it would be simpler and more cost effective to install the smallest AHS coal coal gun boiler being the S130
with 130,000 BTU gross output and set it at summer operating temperatures of 140 low 160 high with a high limit dump temperature of 190 and a differential of 10 degrees.

You could keep the glycol system or use straight water and just be sure that the coal stoker boiler is plumbed properly per AHS the instructions in the owners manual and the local and national plumbing codes.

In the event of a power outage an AHS coal gun boiler will stop
running and hold the fire for many hours

You will save money and be warmer as the slab will stay at a more uniform temperature longer without set backs which would cause any system to run more.

You have a high volume of air space in the building too with no insulation and a thick slab.
I do not think they being the boiler reseller did you any favors in my opinion.

An AHS S130 coal stoker will work well but it cannot placed be anywhere near where you are storing or spraying combustable liquids.

Really no sense in going over a 50- maybe 60% glycol. Freeze protection does not go lower than with a 60% mix. The cost and thickness of 100% glycol would be a deal breaker.

Ojigwan

I will post some more pics of the system later tonight when I get to the shop. Thanks for all the comments.
It is 3/4" copper.
Our in floor tubing is 7/8" PEX tubing I think it was roughly 15in on center.
5 loops each 300' long all on a closed system dedicated to heat the floor. Its a 5 loop manifold.
We have insulated the building. When I first posted we were in the process of finishing it. Other than one wall which will get a big door, the rest is insulated.
We did bleed /purge the system of air, though I plan to do it again this weekend just to be sure that is not one of the causes.
I also plan to insulate the outside of the slab, would 2in green foam board be sufficient for that? Should I use concrete fasteners or an adhesive (not sure it would do much in the current temps)

Zman

I don't think they make 7/8" pex, maybe 3/4"? Getting an accurate idea of your supply and return temps on each tube will give you an idea if you have air or flow issues.
If you can also post the model of the electric boiler, that would help. It has a flow resistance that needs to be considered.
That being said, if the boiler is running at full output, the heat is going out. Getting the flows correct will just make it heat more evenly.

Gordy

They make 7/8 however........

hot_rod

7/8 od is 3/4 pex or copper CTS

EBEBRATT-Ed

I agree with a 25-30% glycol mix is where you need to be. Thicker glycol will slow the flow and the heat transfer will be reduced. Once the slab is warm it's going to be very tough to freeze up, the slab is going to take a while to cool

HomerJSmith

I would kinda like to know where the tube is located in the slab. The optimal placement is 2" from the top of the slab to the top of the pex. If it is laying on the the insulation board with 6" of concrete above it, that's a problem. That is going to be a slow reacting system.

I never use glycol solutions less than 30%. A low concentration can act as food for bacteria. Water quality is also important. Use DI water as a glycol mix if you want your additive package in the anti-freeze to last as long as possible. You should be using an anti-freeze made specifically for hydronic usage.

What speed are you running your UPS-15-58? For curiosity how bout some pictures of your manifold.

HomerJSmith

I would shorten your delta T by increasing the flow thru the pex. You're not running a mod/com. Shoot the slab with a IR thermometer or you can take a thermograph of the slab if you can get your hands on an IR camera.

The green loop is going to suffer greatly if there isn't any edge insulation on the slab. It's too late now, but I think I would have designed the tube layout differently. One good thing, your circuits are balanced.

Ojigwan

Thanks again, sorry the confusion my order form/receipt said 7/8 PEX.
I have an IR temp gauge, but not an IR camera, I will get temp readings today and follow up with photos of the manifold and the over all system.
The boiler is an
Model Btuh Stages GPM
EB-MS-20 68,000 4 2-8

The tubing was secured to the remesh in the slab, when it was poured the remesh was pulled up by rake, tough to know exactly the final height but it should be 2-4 inches from the top and not at the bottom on the insulation.
We are running the pump on it's high setting.

Zman

A quick look at the boiler manual and a couple questions
Are all 4 stages firing? If you have an amp clamp, you an check easily.
Are you running 240 volt single phase or 208 volt 3 phase to the panel? The unit is derated 25% for 208.

Ironman

Use construction adhesive that's made for blue board and Tapcons to insulate the edge and then pile dirt or gravel up against it.

hot_rod

"Quote" rel="Ironman">Use construction adhesive that's made for blue board and Tapcons to insulate the edge and then pile dirt or gravel up against it.

I agree with Bob, that edge loss is huge as it directly see ambient temperature, a huge delta on a cold day. So your perimeter by the slab thickness is the exposed square footage.

The companies that supply metal building steel can bend up unique flashings to cover the exposed foam.

The tricky detail is where a drive or sidewalk slab comes up to the building. They have a plastic H cap to cover 1/2" foam for that detail.

HomerJSmith

Hopefully, the tube was set at 2" from the top. I would have used a serpentine layout with 6 zones, I think. Maybe you are not giving the slab enough time to stabilize temperature wise.

You are going to get the most heat out of the slab at the manifold because that is where the tube spacing is the closest and heat energy the highest. Everyone expect the slab to feel hot. That's not how it works. The slab may be just slightly above body temperature and still make the environment comfortable.

I don't see any 1" PVC ell's covering the pex where the tubes exits the slab.

I don't think it is 3 phase, but, what do I know. That takes a different transformer and wiring by the power company which they usually want to charge you for.

HomerJSmith

When I have had to put rigid foam insulation on the outside perimeter of a building, I have covered it with 1/4" Hardy Backer Board which is an underlayment for ceramic tile.

HomerJSmith

That's Hardie Backer Cement Board!

Gordy

find any siding company that owns a break. Buy a 2’ wide roll of coil stock color of your choosing. They can make you 10’6” lengths to cap the foam insulation. 2” double fold 90 degree on top to cap top of insulation which leaves 20” of vertical coverage.

Another method to fasten insulation is pinch nailing with a 3/16” hammer drill bit, a piece of rebar tie wire in the hole drilled, 3” insulation washer, and 16 penny nail. Tap cons can get pricey, and you should use the insulation washer with either method. Either method requires a hole drilled.

hot_rod

Most tool rental shops rent those long breaks for flashing work. They are fun and easy to drive for simple bends.

One caution, I used that aluminum roll flashing to cover the ICFs on my shop where the Hardie siding came down to the foam. A weed whacker, operated by my lovely, pretty much destroyed it.

Also the stuff the box stores sells is paper thin, roofing suppliers have a better gauge.

I prefer the heavier gauge steel or Galvalume for exposed. ground level flashing.

rick in Alaska

And if you are in an area subject to frost heaving, make sure whatever you backfill with has good drainage or it will rip the metal right off the foam.
Rick

Gordy

hot rod said:

Most tool rental shops rent those long breaks for flashing work. They are fun and easy to drive for simple bends.

One caution, I used that aluminum roll flashing to cover the ICFs on my shop where the Hardie siding came down to the foam. A weed whacker, operated by my lovely, pretty much destroyed it.

Also the stuff the box stores sells is paper thin, roofing suppliers have a better gauge.

I prefer the heavier gauge steel or Galvalume for exposed. ground level flashing.

Yes there is always the lovely wifey to be helpful

I remember when I did new 6” gutters with 3x 5” downspouts. A squirrel could easily go up the 5” downspout. Lots of bur oaks, and acorns.

Only to come home after the lovely Sandy mowed the lawn to find a couple down spouts squished shut.......never knew she did it. Backed into them with the bagger hopper on the back. Once pointed out by me the dilemma was my fault, because I increased the downspout size which infringed on her precision mowing tactics. In which are done exactly the same, and the old 3x4 downspouts were never a problem........

Of course she was right. If I wanted her to continue mowing operations

Ojigwan

All really great comments, thanks.
Power is single phase 240v. Total service is 200 amp, a friend who is a commercial electrical installed everything.
All 4 boiler stages are firing.
We still have some exposed spaces where we haven't finished insulating yet and the heat transfer is incredible, like a cold fan.
I think once we finish up all the insulating and install the outside foam board around the slab we will be feeling pretty good.
Update: I used the glycol tester and it was around 17%. I decided to just flush it and use water only. My logic was that at that concentration it wasn't providing much frost protection, but I was losing efficiency.
Below are the temps when I entered the building and a few pics.
Yesterday the outside air was 38F so it has come up a lot since my last post,
Inside the air was 77F
Inlet temp: 125F
Oulet/Return: 85F

What should I expect once the slab is up to temp and we have reached desired air temp for the delta between input to slab and output from slab?

Ojigwan

HomerJSmith said:

Hopefully, the tube was set at 2" from the top. I would have used a serpentine layout with 6 zones, I think. Maybe you are not giving the slab enough time to stabilize temperature wise.

You are going to get the most heat out of the slab at the manifold because that is where the tube spacing is the closest and heat energy the highest. Everyone expect the slab to feel hot. That's not how it works. The slab may be just slightly above body temperature and still make the environment comfortable.

I don't see any 1" PVC ell's covering the pex where the tubes exits the slab.

I don't think it is 3 phase, but, what do I know. That takes a different transformer and wiring by the power company which they usually want to charge you for.

Can you elaborate on the "I don't see any 1" PVC ell's covering the pex where the tubes exits the slab. " comment? I don't think I understand what you are referring to? Should I put pipe insulation on my copper going into and from the slab?

Zman

The IR gun will not work very well on the brass,copper and pex surfaces. If you wrap the pipe in electric tape you will get more accurate temp reading.

If it turns out that you have a delta of 40 on your radiant supply/return temps, I would recommend increasing the flow.

The 3/4" piping (not to mention the garden hose) is constipating the flow in the boiler piping. Ideally the piping would be 1". Swapping the 15-58 circ for a 26-99 would also help.

I would still verify that all 4 stages are firing with an amp meter. The relay lighting up is no assurance that the element is actually working.

ratio

What @Zman said.

The IR gun, without calibration, isn't too reliable on absolute temp, although ΔT readings over time or similar spots are generally valid, as long as you take care to get in the same position to reduce background interference. Knowledge of the aspect ratio helps.

With a ΔT of 40°, you're either under pumping, still charging the slab, or a combination of both. Do you have any way of getting a ΔP from somewhere? That should help narrow it down.

Gordy

I think you will be fine once thermal equilibrium is reached. Like @hot rod said 64000 lbs of mass.

hot_rod

If most of the tube is at the bottom of the slab, you may need to crank the supply temperature also. Hopefully some of it was lifted into the middle or upper part of the slab.

This model is for a 4" slab, notice the output hit as the tube is deeper in the slab. To achieve a 30 btu/ sq ft on this example would require around 134° SWT.
About 102° for a 15 btu/ ft output.

HomerJSmith

Well, when we bring the Pex out of the concrete, it normally has a pvc 90 deg electrical sweep over the tube to protect it from abrasion with the concrete which could lead to the Pex being cut. Pex expands at 1" per 10' per 10 degrees change in temperature. I think I got that right? Anyway it is constantly expanding and contracting as the temperature changes. Where it is locked into the concrete, the tube walls get thicker or thinner. The movement where it exit the concrete can cut the pex.

I didn't see any sweeps in your photo of the manifold. I'm blind in one eye and can't see out of the other, so I might have missed it.

The reason that I would have done the tube layout in a serpentine pattern is the I can then cut control joints in the slab easier. Where I plan to cut the control joints I cover the Pex with pvc pipe for the same reason as I stated above, abrasion. Also, it is a more balanced layout temperature wise.

As the slab expands and contracts, the control cut allow the slab to crack at those cuts instead of randomly on the slab. Look at the slab the next time you go to Costco. About every 10' X10' square.