Radiant Heat - Before I pour

[GoodStuff]

I am building a 40 x 60 shop - have much of the grading completed and am planning the flooring system. I have already purchased 2" ISO board to insulate under the floor and along the sides. In the process of ordering the 1/2" PEX pipe to run my laterals at 1' spacing apart. Will tie them into a manifold and have under pressure during the pour. The question is... I have read that a seperate pipe is needed to run the thermostat into the concrete. Should I plan on installing a 20' run of 1/2" pipe with a cap on the end to insert the thermostat into the concrete? Any other planning issues I need to address?

 

[yeldogt]

That's what I do for the slab sensor -- keep it away from the other tubing. What's you location ? constant temp ?

I typically go a bit tighter with my loops -- but ?

Make sure you don't exceed total loop length

 

[Chris705]

I did not put a slab temp sensor in my slab. Was going to but didn’t get to it. I use a WiFi t-stat which works well keeping my garage at my set point. When I was starting it up I used a thermal laser gun to measure all sorts of temps every where on the floor and on the boiler pumps to measure the temperatures. Honestly I don’t know if I miss knowing the slab temp at all. I know it’s warmer than the t-stat set point. Would you use the slab temp sensor as a way to regulate the space? Just curious.

Btw you said ISO insulation, polyisosanurate insulation?

 

[GoodStuff]

Yeldog… So far planning 9 loops at 275' each 1' apart. Location is Lexington, KY I could do 12 loops at 210' each if you think appropriate... just figured the volume would be greater with 9 loops and still under the 300' maximum everyone advertises. Do not have Natural Gas at the property. Propane here is very expensive. An electric boiler is $2300 - probably going to use a 27KW instant water heater for cost reasons - roughly $800. Using Mike Bloomington's shop review as the go-to for information... Seems like he has done a tremendous amount of research for all of us already...

 

[GoodStuff]

Chris... 2" Blueboard from Lowes... Plan on using a thermostat in the shop to control the heat, but have heard many suggest an in-slab thermostat as well... without enough information at this point, I am simply making sure all my options are open.


Have one more question... Have a clay base with what will be approx. 4" gravel base for the concrete. I have read several conflicting reports on here of how to best do the vapor barrier. My idea is to run 6 mil plastic, then lay 2" insulating boards. Some say tape the edges, some say the vapor barrier will suffice. Staple the Pex to the insulating boards, and install 6" mesh on 2" risers over everything. Getting 5" concrete floor. Anyone have a different method? Do I need to tape the blue boards?

 

[yeldogt]

I tape the blue board -- just to keep it in place and concrete on top -- I VB under the BB

Electric is more expensive around me .. unless hp .. vs propane. Only you can decide on this.

Typically I'm doing 4" slabs or a bit more ... or wet bed tile. I just tie the PEX to the mesh. I don't know how you plan on using the shop. Closer tube layout provides more uniform slab temp and faster slab warming/ response. Shorter loop length will allow the temp to remain constant throughout the loop. Concrete is high mass and will not heat as fast as say a warmboard product that is also 12" spacing


In an industrial setting 12" on center loops work for warming the slab provided you have constant recirculation. It's all about delivering BTU's to the slab. If you think of a cold slab -- as the hot water enters each loop it is giving up heat tot he slab and comes out the other end colder. Each loop slowly heats the surrounding concrete until the heat from two loops next to each other meet. The goal in any system is even slab temp and lowest temp. Better insulated buildings can get away with greater spacing as the slab temps can be lower.

A building with a higher heat loss will require hotel temp water in the tubes -- depending on spacing.

Did you do a heat load on the building? That will give you the total BTU's and then you can figure out the BTU's needed per square foot .. that will give you the water temp at a given spacing.

Also if you have an area where you will be working -- you can decrease the spacing and provide more BTU's to a particular spot w/o needing to change temps. You can even make this an extra loop and keep it off if you don't use all the time.


There mare many strategies -- extra loops per code areas -- counter flow (reverse) looping .. so the hot of one mates to the cold of another for more uniform slab

 

[kj_mustang]

Did you do a heat load on the building? That will give you the total BTU's and then you can figure out the BTU's needed per square foot .. that will give you the water temp at a given spacing.

Plus this will help you know if the heater can supply the proper gpm of water at the proper temperature. Do you really know if that 27kw heater is adequate?

 

[Chris705]

Regarding the need or not for the wwm to be at the middle of slab or on bottom of pour and there mainly to tie pex to....If your base is firm enough, welll compacted and totally settled you don’t need the reinforcement(we’ll placed sawcuts will control the cracks) However it does make a great anchor for the pex and the 6” spacing really helps with pex layout, keeping runs straight and conforming to a layout. My base was exposed to the elements for almost 9 months and took a pick ax to dig my plumbing lines into it. It isn’t going anywhere and your base sounds similarly firm.

I used 10 mil yellow stegowrap VB under my insulation board. Lap joint by 12” or use a tape of some sort.

 

[Randy in Maine]

I don't even have a slab temp sensor in there. I just use a wall mounted thermostat.

 

[4cyclic]

I have installed about 10ft of capped tube for the slab sensor. It is useful to have as you can monitor both air and slab temps.

 

[850xpeps]

I have installed about 10ft of capped tube for the slab sensor. It is useful to have as you can monitor both air and slab temps.

Rebar in the slab. I’m not sure why people don’t put it in. And tie your pipes to it. Makes for fast easy layout and I would prefer it in the cement not on the bottom.

I’m curious as to how you would do a load to measure what btu you require? Also I think I would keep loops shorter than 250’

 

[kj_mustang]

Manual J calculation

 

[Jackfre]

I always add a bit of Oil of Wintergreen or Peppermint to the tubing during the pour. Put the system under pressure and if some meathead breaks the tubing, you know it and can get the repair done then.

 

[buildingup]

Just had my barn poured a couple of weeks ago. I did run a separate line of pex for the sensor if I decide to use it and have not found the thermostat I will be running yet. My pex is 15" on center with the load I had calculated for it and the heat losses. Also stapled the pex to the foam board (lot easier then zip ties to rebar/wire mesh) and don't have to worry about a puncture to the pex from sharp metal. Pressurized the system to 100psi with compressed air a week before the pour as well. Pic for reference.

20180517_183648 by Julian Lopacki, on Flickr

 

[yeldogt]

Running the tube for a slab sensor is so cheap and easy there is no reason not to do it -- this gives you some flexibility should you want to add in the future.

Tubing spacing and layout is first about getting the proper BTU's -- second, about overall use and particular use. You can do a lot of heat management with proper tubing layout that allows for very simple adjustments at the manifold. All of my spaces have benefited from some modification in the tubing layout

 

[coldh2o]

I have radiant floor in my basement and forced air gas in the rest of the house. Although the vents in the basement are closed during heating season, the temp down there is still somewhat influenced by the system upstairs. I run the radiant floor thermostat on the slab temp sensor so it isn't reacting to small air temp changes, particularly because the forced air is on a setback thermostat.

It did take a bit of trial and error to find the correct slab temp setting.

 

[yeldogt]

I have radiant floor in my basement and forced air gas in the rest of the house. Although the vents in the basement are closed during heating season, the temp down there is still somewhat influenced by the system upstairs. I run the radiant floor thermostat on the slab temp sensor so it isn't reacting to small air temp changes, particularly because the forced air is on a setback thermostat.

It did take a bit of trial and error to find the correct slab temp setting.

A slab sensor is a good way to warm a floor when you have a second system in the house -- the floor presents as warm but it's not providing all the heat required. They are great when you are adding heated floors to an existing kitchen or bathroom. I have a glass solarium and in the winter the heat required would make the floor too hot -- the slab sensor cut the floor off at my determined max and the panel system w/ thermostats takes up the slack.

 

[Lelandwelds]

A slab sensor is a good way to warm a floor when you have a second system in the house -- the floor presents as warm but it's not providing all the heat required. They are great when you are adding heated floors to an existing kitchen or bathroom. I have a glass solarium and in the winter the heat required would make the floor too hot -- the slab sensor cut the floor off at my determined max and the panel system w/ thermostats takes up the slack.

Interesting read. Cold is almost a foreign language here. I see cold weather in the teens once about every ten years or so. Some winters it never hits freezing.

Would infrared complement slab heat better than forced air?

 

[yeldogt]

Interesting read. Cold is almost a foreign language here. I see cold weather in the teens once about every ten years or so. Some winters it never hits freezing.

Would infrared complement slab heat better than forced air?

infrared is radiant heat --- anything that heats up will radiate. A slab floor is a big radiator. In old houses where the floor BTU's output will not meet need -- the use of supplemental radiators -- panel / Runtal was my preferred way. It really depends on the shortfall and how often. Modern heat pumps able to work in cold weather can now often do the job.

In new well insulated buildings -- you can actually have too much heat from even a slightly warm floor.