Anyone here use an in slab radiant floor with a he condensing ng boiler?

[Mike Heidrick]

Ive been researching he condensing ng boilers for use with my radiant floor. If you are using one what size is your building building, how much insulation do you have, how much pex, what size pex, how many loops are you using and how many zones? Also is it copper or stainless and are you using well water.

I have 2600 ft of 1/2 pex in 9 loops in one zone in the middle of 5" concrete that is foamular under and perm insulated with a moisture barrier. Walls will be r19 and no ceiling insulation picked yet. 40x64x16

Also researching this on garagejournal. I have a quote from hydrosmart on their condensing 120 boiler and a panel but am also looking to see what others are running.

[Carl Weber]

MIke, I too have Slab radiant. I heat 1200 sq ft. with 1500 feet of 1/2" Pex in 6 loops. I use a on demand waster heater and it work just fine. I am on Propane (expensive) but that is my only liquid fuel option. System works fine. For my application I could not see running a boiler. I know this dose not help with what you are looking for. But it is one many different setups that I am sure will be posted. Good Luck on you choice. Sounds like you will have a nice shop.

[Mike Heidrick]

The setup i got qoted sure looks at an on demand water heater. They are billing it as a boiler and it is designed low low temps and is closed loop.

What brand model and size is yours Carl?

[John C Bush]

Hi Mike, I heat my 1500 sq ft shop with ng hot water heater. Simple system--heater, pump, manifold for 4 loops, relay, and thermostat. Also provides HW for sink. HW tank is standard 60(80???)gal, high efficiency that vents thru the side wall. We don't get the extreme cold weather out here as you do back there(I grew up near Danville, IL and I remember the winters) and I usually keep the thermostat @ 60. Slab holds heat well and is always comfy. Plumbing buddy did the design?install and has worked perfectly for 15 yrs.

[Bill Rabbino]

I heat my 2200 sq ft shop with 7 loops, one pump and balancing valves. I use a Munchkin propane fueled condensing boiler. My slab is 4" and has 2" of rigid foam underneath. The building is metal with 10' ceilings and only has 1" of spray foam insulation. The manifolds are Wirsbro (now Uponor). the building maintains set point temperature when it went to -1 degree.

[William C Rogers]

Mike, I am using a NG on demand heater. I didn't really spec it out as I was building a house and didn't have time. Mine is the model 240 on the attachment below. It does work ok. I just keep mine at 50 most of the time. However it is located next to a window and center of the shop is warmer. It is definitely not a fast heat up. The unit is set for a 2 degree drop before coming on. When it got to the minus temperatures the temperature dropped to 44 before coming back up,to set point. Other than that it maintains very well. My system is only two loops and one zone. My shop is 30 X 50. They have bigger units than mine. It is hard for me to figure my cost as the gas company keeps estimating the bill and I am using gas backup to my Geo and cooking, clothes drying. It is somewhere between $75-100 dollars per month.

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[Tom Hyde]

I can't speak to your specific setup, and I don't use gas, but I've been extremely happy with my 1200 sq. ft. radiant slab in the shop using a 9kw electric mini-boiler. We have cheap power and mild winters in the Northwest so it was the best application for me. I estimate power cost at about $2/day, at the most, during coldest months of winter. We do get temps down to the mid teens, though rarely below that. The system has been operating for nearly 5 years.

Since I've relied on posts like these in the past, I thought I'd go into a little more depth for the sake of the archive. I put in this system myself after a LOT of research with no prior experience. Good information here and other forums helped a lot.

I have a 32'x36' acid-stained concrete 6" slab on top of 2" foil-faced rigid foam. This slab "floats" within 3' stem walls infilled with 2' + of compacted gravel covered with a layer of compacted sand. 2" Rigid foam is around the inside of the stem wall with the top cut at a 45 angle to permit concrete over the top of it. In this setup, a control joint around the perimeter between the edge of the slab and the stem wall is critical to prevent cracking. The thick slab also keeps the shop cool in the summer.

The slab has rebar on 2' centers throughout sitting up on dobie blocks, with 6" wire mesh tied on top of rebar. Radiant Tubing (1/2") is run on top of mesh and zip tied to it. That puts the pex pipe in roughly the lower third of slab where it should be. Kerfs (roughly 1/8" wide x 1/8" deep) were later cut into the floor with a diamond blade on a circular saw on 3' centers in a diamond pattern. That was fun. Five years later, there isn't a single crack I can find anywhere in the slab, though there may be ones I can't see in the bottom of the kerf cuts which serve both a decorative and practical function.

The radiant system is a closed loop running at about 15psi with four loops of 250' to 300' each. There is only one zone which keeps it simple. I like simple. I seem to remember I was at about the max on both the feet per loop and the feet per zone but it's been awhile. I also installed the boiler panel and piping myself using the recommended setup from the boiler manufacturer. Thermostat is connected to sensor in the slab and boiler. Works very well. The radiant panel is pretty straightforward using black pipe (photo below). Be sure to wear gloves, those threads will slice up your hands.

First post here, trying to pay back all the great information I get here all the time. I hope this is helpful.

A few pics.

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Walls, shower, toilet spray painted on foam board to help with tubing layout.

hyde_tom_shop2.jpg
Back of the pickup with spool on two pieces of rebar. Best way to run your pex tubing.

hyde_tom_shop.jpg
Never been so nervous as guys walking all over my pex during the pour, but only way to do it.

hyde_tom_shop4.jpg
Pex is pressurized before the concrete pour. My role during the pour to make sure there are no breaks.

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Electric mini-boiler and panel. Four loops, one zone, pretty simple.

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Finished floor, with control joints (and edge of compass).

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Tubing layout. So glad I meticulously planned this first.

[Dale Barber]

Mike -

Tom has given you lots of good input above.

I built my shop 7 years ago. Front part is a 28 by 56 area (1,568 sq ft) with a slab that is nominal 5 inches thick. Has a 2 foot square grid of #6 bar over the entire area but no mesh. PEX was zip tied to the rebar. 6 loops (and all loops were designed for 250 feet +/- 10%f but did vary more than that). Above the main part (44 foot portion) is a roughed in 740 square foot apartment space that has 6 loops with foil faced insulation under the pex. I have never charged these loops with water as I have never finished and used the space, other than for storage. But even with no heat it has never gone below 50 degrees. The apartment has a separate zone pump and thermostat. This part of the shop is a 3 1/2 car garage with a 12 by 24 metal bashing room off the side. There are 6 loops in this area, as I said tied to the rebar and on top of 2 inch foam. One thermostat and pump services this slab area.

Immediately behind (44 foot wall separates them, with 2 man doors) this is the wood shop, which is 24 by 44 (1,056 sq ft). Since the ground slopes it ended up being just about as efficient as anything to stick a cellar under this part with a garage door out of the cellar in the back, which opens into an implement shed lean-to that is open on the long side. Cellar walls for this and stem walls for the front part are all ICF construction. Cellar slab has 4 loops but run off the thermostat for the wood shop immediately above. Although I charged all 4 loops I have isolated the three 'inner' loops and only heat the outer loop. These loops were placed using plastic standoffs that 'screwed' into 2 inch thick foam insulation. The wood shop uses PEX stapled up and 6 loops. Eventually I will add foil faced insulation here, but I still do not have final wiring or dust collector piping run - hopefully in a year or so.

We are very fortunate - the 'last stop' on the gas main out of town. Using a Triangle Tube Prestige boiler - modulating condensing. System has been fantastic. I calculated the design heat loss for the entire building at 79,823 btu/hr at -10 degrees F. Unit has domestic hot water capability which would handle the apartment so supplies all I need - but I keep it pretty well turned down. Only issue with boiler was failure of the integral low water shutoff sensor at the start of the second heating season. With the capability of the unit it was easy to isolate and I got the part under warranty. I keep both thermostats set at 62 and the shop is comfortable to work in all winter - although I do by habit wear a long sleeved tee shirt and a flannel shirt to work. We had the coldest February on record here (upstate NY) this year - gas bill I just got for that month was $72.60. When I was planning the shop I analyzed also on a wood fired boiler as I was not sure at that point if we could wrangle the gas line extension. I'm very glad we got the gas - system was cheaper to install than a good wood system and a lot less work on a yearly basis.

This building is very well insulated and sealed. But it has two large garage doors on the north side and one small one on the south side. I used treated lumber for the thermal breaks at the garage doors. Will also add I did the design of everything, with a bit of help from local plumbing supplier in sizing the boiler. Installation was by me and a contractor friend - he usually does not do heating systems any more but made an exception in helping me on this build.

If you have any other questions don't hesitate to ask.

Dale