Help! I was going air source HP but over the weekend some $$$$ came to me and I was about to pour the basement concrete floor this week. Now I put the delivery on hold as I scrabble to get bids and smarts on geothermal grd. 2400 sq ft main level, same size but only 1800 sq ft finished walk out basement. Need to get smart on floo rradiant heat systems and installation. Can I do this part, do I need a professional to lay out the dimensions etc..... Any help is appreciated! Lisa

basement is one big open space? If so, keep your loops to 250 or less, do 12" o.c., and make sure to use 2" of rigid foam underneath. that will buy you some time to get the rest of the system figured out.

If you have rooms, make sure they are isolated on their own loops, don't run two rooms on one loop unless they are non-critical rooms like closets or halls.

No matter what you do, a radiant floor is nice to have.

We can provide a pipe lay out design, pipe manifold and tools to attach pipe to foam should you need.
Do lay the pipe in on 2 inch foam, 12 inch pattern is about right, I prefer a 9 inch 300 foot loop. If you chose not to use the hydronic side for several years that's ok, one day some one will, you can never install after the cement is poured.
Dan

I'm not sure why you would ever need 9" o.c. tubing in a basement, unless you're daylight with a lot of glass. 12" o.c tubing will run at a lower water temp in a basement than anything else in the system will anyway.

I found when I installed regularly before I got involved with sales that the difference in cost running 12 inch pattern VS 9 inch pattern was nil example;
1500 sq ft x 1 pipe foot per square foot = 1,500 feet of pipe @ .285 foot pipe=$427.00 5 circuit manifold 173.00 $600.00
1500 sq ft x 1.4 pipe foot per square foot = 2,100 feet of pipe @ .285 foot pipe=$598.00 7 circuit manifold 211.00 $809.00
Heat saturation just went up 20%, no potential cold spots when pattern gets a bit beyond 12 inches,
net difference in material cost $209.00 plus labor. Whats the value of the home, client ?For me it is a small price to pay that guarantees customer satisfaction. In our region average homes that have in floor heat are starting in the $300,000.00 range and hitting regularly $500,000.00 plus . An extra $200.00 per 1,500 sq ft is excellent value for the returns.
Can you do it on 12 inch, sure. no problem.
Dan

it'll work, but I've never met anyone who could.. or has.. picked out stripes at 12" o.c. in a residential thickness slab. I don't think there is any return on the value there.

Again it is easy to do, you can recover a cold slab quicker, the cost is minimal, and its effective on those occasions where your on that last loop of pipe and stretched so thin that your pushing to a 15 inch pattern, with the blanket 9 inch approach on staple downs and slabs it eliminates the potential for any cold spot. A small price as contractor to pay for the absence of any complaints.
The contracts we ran were profitable and this was the cost of business.
Every body has there own way of doing, this was mine.
Dan

Does no one here do heat loss analyses and water temperature analyses on conditioned spaces before the 9 inch versus 12 inch decision is made? 9 inch will yield one desired water temperature and 12 inch will yield another. In concrete especially, the water temperature and the spacing need to be close to correct to prevent large temperature swings.

Sure, heat loads are just a big guess anyway (well, sort of) but gosh, if you're going to design a mechanically stable radiant heating system, the least you could do is start with a sound design. I don't see how you can make a 9 inch versus 12 inch decision if you have no information on the specifications of the room, even if it is a basement, and you can always go from 1/2 inch PEX to 5/8 inch PEX if you need to do so. To always use 12 inch spacing, or always use 9 inch spacing, well, that just seems a bit lazy to me.

Jeff

I ALWAYS do heat load analysis. Without this information you literally don't know what you are doing. You are correct; tube spacing will effect design temperature, as will tube depth, water flow and emitters used for sub-floor or sandwich applications.

Generally speaking, the closer the tubing spacing and the closer the tube is to the conditioned space, the lower the operation temperature can be. Tube size is more a factor of tube length and flow (the last factor I consider in the design process).

As for heat load analysis being "just a big guess". I have spent a considerable amount of time and money going to radiant floor, system control and boiler manufacturers' technical seminars, learning residential Manual J8, and applying sound ASHRAE engineering practice with Wrightsoft application software.

After considerable practice certain common patterns do become apparent, but can turn in to bad habits if conditions in construction dictate a change from the "normal" spec. However, I submit WAG engineering is for the novice and perhaps the lazy, as you suggest.

Jeff, i always do load calcs as well. and fact is, in a basement, 99% of the time 12"o.c. is fine, and even wider would be fine if it weren't for noticeable heat striping. I still always do the numbers, but the vast majority of typical basements are approximately 10 BTUs/sq ft or so, and even with carpet your max water temp there would be under 100 degrees at 12" o.c.. Now, I design 100 degree max temp systems routinely, but the fact is it's pretty uncommon for the water temperature to be highest in the basement. Usually it's set somewhere else in the house.

Sometimes people come the realization that they need some design done too late. The good news is though, the first thing up is usually the basement, and the basement usually requires the least amount of design to get right. Such as, in the case of the original poster here.

The only time I have ever seen a 9" o.c. justified by any water temperature need in a basement is daylight basement with a carpeted room on the daylight side. The numbers rarely indicate the need for anything other than 12" o.c.: they primarily just tell me what my flow rate requirements are and thus whether I can run the 1/2" maximum size loops to 200, 300, or 500 foot loop lengths. There is never a need to use 5/8" pipe in residential basement slabs and rarely a need in commercial for that matter.

If you're going with geothermal, keep in mind that the efficiency is definitely affected by the loop spacing and thus the loop temp you need to have. Water-water heat pumps will produce up to 120F water, but at a much lower efficiency. If you can space your loops 9" or 6", you will only need to run 90-110F water, increasing the efficiency of the heat pump. This can make an efficiency difference of up to 0.5 COP (which is to say 50%).

I will reiterate that in a basement slab situation, the max water temp is not likely to break 100 deg F even with 12" o.c. spacing. 6" o.c. in a basement slab is completely unnecessary overkill.

 

12” oc is a “standard”. It’s a standard because it works in the majority of situations. It’s the job of the designer to start with the standard, then deviate from it, if necessary, after looking at all other design criteria. I have to agree with NRT.Rob though… I’ve never had issues with striping on a 12” oc slab. And, as far as “stretching” that last circuit, well that’s a design issue in it’s self, now isn’t it.

BTW… I think we have deviated from the original question a little.

 RadiantRob