I got an estimate for roughing in the 1/2 inch radiant tubing in my 40X40 shop building. I was planning on doing the tubing install myself but time and distance have me looking at paying someone to do the tubing and manifold installation.I requested that the tubing be attached to the welded wire which will be placed 2 inches off the bottom of the slab. The radiant heat guy (20 years of experience) informed me that attaching the tubing to the metal is too labor intensive and he suggests stapling it to the foam. I questioned the efficiency of that method and he told me that the heat will travel thru the whole slab and where you place the tubing has no effect on how well the system will perform. I am certain that on another thread here it was suggested that placing the tubing on the bottom of a 6 inch slab was not the ideal place to put it. Am I being too picky?

His estimate for all materials and labor to install the six tubing loops (265 ft each)and a 6 loop manifold set with flow meters and flow adjustment valves was $2870.00. That price includes all staples, tubing, bend supports, manifold set and any thing else necessary to complete the tubing install. He did not break down the estimate into parts and labor nor did he say what brand of tubing or what type of manifold he intended to use. This seems really high to me. Does any one with experience actually installing tubing have any input on how long this should take and if this estimate is reasonable or not? Thanks for your replies in advance.

Kerntrans

You can calculate the efficiency of the HR emitter by calculating the ratio of the R-value above the PEX tube and below the PEX tube. One typically doesn’t want more than 5-10% of the heat supplied by the PEX tube to go downward and be forever lost. You are looking at a couple percent of lost HR emitter efficiency by placing the PEX tube at bottom of a slab. Many folks find this to be an acceptable tradeoff between HR emitter efficiency and HR emitter construction ease. A concrete slab HR emitter is way more efficient than an above-floor or below-floor emitter, so you will have a very efficient HR emitter in any event.

You can price the tubing and manifold by shopping online. I assume the under-slab installation is NOT part of this estimate. Placing 1600’ of PEX tube shouldn’t take more than 6 hours, so you can figure out the hourly rate and decide if it is high or not. We try not to comment on other company's rates, etc.

A 6" slab will exhibit quite a bit of thermal lag (i.e., it will take a relatively long time to change the slab temperature). This should be fully considered and addressed as part of the overall building integrated design. I would highly recommend using thermostat(s) that use both air temperature and slab temperature sensors and a heat source that uses outdoor temperature (outdoor compensation/reset) to adjust the supply temperature and better maintain the desired indoor comfort level.

Correct, no insulation in the quote.

I just thought of another question. If I plan to keep this shop warm all winter will it be safe to just use water and not a glycol solution? Shop is in NW Montana, 99% dry bulb temp is -5. Not needing freeze protection sure makes the overall system simpler since it will be integrated with the house radiant also.

OK,
40x40 = 1,600 sq ft
Montana I like a 9" pattern, yes staple to foam is good and fast. Rebar on top if needed not wire mat, to many sharp edges. Fiber mesh added to concrete is also good.
1,600 x 1.4 = 9" pattern 2,240' pex. reality 2,100' is good
Our shop we offer: loop layout, stainless steel manifold, 7x300' barrier pex, staples, rental tool few odds and ends runs you about $1,000.
Labor takes about 1 day and some sort of libation.
You might want to find the time,
Dan
A little glycol can provide some winter security perhaps 15% max would be 30%

If you are certain the PEX tube won't freeze, you are better off just using water as gylcol solution reduces the HR emitter efficiency and also reduces the circulator efficiency. But if you are at risk of freezing the PEX tube, you need to use glycol solution.

I use rebar wire tie to the mesh for pex attachment and is very quick and good. I have also stapled the rebar ties to wood floor for inside slabs. Very cheap and strong.

For a shop, you may even be able to use a 18” PEX tube spacing. Less total tube and less required manifold ports translates to less cost. A 12” PEX tube spacing is the largest recommended spacing for a residence where you don’t want bare feet to sense any floor temperature gradient. However, this typically isn’t a design criteria for a shop. One really needs to determine the required Btu/hr/sf of floor at the design condition to sort out the best PEX tube spacing and other HR system design aspects (i.e., accomplish an ACCA Manual J8 heat loss analysis or equivalent).

The design heat load is 29949 BTU/Hour for the shop.

I would recommend going with either an 18” spacing (1068’ of PEX tube and 4 port manifold) or a 12” spacing (1602’ of PEX tube and 6 port manifold). A 9” spacing would also work fine and will have lowest required supply temperature and circulator capacity, but would be more expensive (2136’ of PEX tube and 8 port manifold) and this small spacing is not needed for a shop with your low heat load.

For a shop, I would recommend a 20F delta T design (normally a 15F is recommended for residential applications for aforementioned bare foot comfort). No matter what spacing you use, your total required flow rate is 3.06 GPM given your low heat load.

At a 9” spacing you will have 0.38 GPM in each of the eight 267’ circuits at 99F supply temperature, 79F return temperature, and a total required pumping head of 2.4'.

At a 12” spacing you will have 0.51 GPM in each of the six 267’ circuits at a 101F supply temperature, 81F return temperature, and a total required pumping head of 4.1’.

At an 18” spacing you will have 0.77 GPM in each of the four 267’ circuits at a 106F supply temperature, 86F return temperature, and a total required pumping head of 8.3'.

At your low heat load, you could consider a simple NextGen-8 electric boiler (8 kW or 27,300 Btu/h) if your electric cost makes this feasible. The NextGen boiler is really a HR appliance that just hooks up to the manifold and you are done. It has many nice features.

NextGen Boiler

If you are going to larger spacing the deeper in the slab the tubes are the less you will notice temp variation for when you "walk around in your bear feets" in your shop.

18 inch spacing would work good also if you were attaching it to wire mesh because the mesh squares are usually every 6 inches and that would help with your layout.

I have many times put down mesh in complex shapes, pulled the mesh outside, put the tubing on it and rolled it up to take back in. I have also flipped the mesh put the tubing on and flipped it back for a six inch slab. this put the tubing at the bottom but spaces the mesh off the bottom of the slab nicely because no one can pull up during the pour and get the mesh at the right height without using chairs.

Yes, at an 18” spacing the floor will NOT be bare foot friendly. One normally doesn’t care about that in a shop, but if you do, then use a 12” or 9” spacing.

We have used hooks to pull up many miles of PEX tube attached to the top of wire mesh. It does take a concrete crew with the skills to do so. As Dan indicated, you do have to be very careful about sharp things on wire mesh when working with it. Often times wire mesh is also inadequate for structural reasons and rebar must be used. There are also times when you simply can’t pull up wire mesh or rebar like for example when you have to pour a very large slab in multiple staged pours because you are coloring and stamping the concrete to look like wood plank, etc. and you can only do about 500 square feet at a time. In this case we either chair rebar on EPS insulation and then tie the PEX tube on top of the rebar or we place the PEX tube on top of thicker EPS insulation (i.e., 4” Hydrofoam) and then chair the rebar above the PEX tube. I have attached some photos of the latter (4" thick Hydrofoam, 1/2" PEX tube, #4 rebar, 5" thick 4000 psi 0% air slab). In short, you do what you have to do to maximize the HR emitter efficiency while still successfully accomplishing the desired finished floor requirement.