getting pex for staple-up radiant to heating area

[herron1967]

I am adding radiant heat to the first floor of my house (replacing water baseboard heaters).

My basement does not have a ceiling, and I have been trimming flooring nails that protrude into joist bays from the first floor.

My question is this: plumbers have told me that I should have runs of

200'-250' for radiant pex (3/8"). This means 200'-250' of actual heating area as opposed to getting the pex to the heating area. To get the pex to various heating areas under rooms, I would like to run it through large pvc pipes so that I do not have to drill enormous holes in floor joists. I'll have to drill some holes, of course, where pex crosses joists in the middle of a run. My thought is that I would run 3" PVC along a large beam in my basement and put Ts in the PVC where a pex run starts. There will be another T where a run ends and begins to loop back to a manifold. The PVC will house a number of pex runs to heating areas and will protect the pex since at some point I am going to have a shop in my basement.

Is there any reason not to do this? I have seen a few radiant heat setups, and they always have ganged up pex running all over the place. My thought is to organize and protect the pex by putting it in large PVC pipes on the way to a heating area (where it will run in joist bays with heat transfer plates).

Comments would be highly appreciated.

Thanks.

Mike

[HeatMan]

Okay...

That's always a problem.

The max run for 3/8" PEX is 300 feet, if you want the system to actually provide heat.

Sounds to me like you're making it much too complicated. If you're running

3/8" PEX, your holes need to be about 7/8".

You said a magic word, Heat Transfer Plates. Describe them to me, thickness and legnth. What water temp will you be running through the PEX?

You got my comments....

Yer Welcome....

[herron1967]

Ok, good, so I am fine with 200'-250' of heating. I'll keep the runs closer to 200' just to be conservative.

What I mean is this. I am going to need probably four runs of 200' or so to do most of the first floor. The runs will start at the boiler, of course, and go in a similar direction on the way to a heating place. Can I protect the runs by putting them in large PVC before they get to a place that they heat, i.e., with heat transfer plates? This is just a way of hanging one PVC pipe and having the pex tubes run through this on the way to a room in the house. The PVC pipe will be functioning as a raceway. Without such a raceway, I will end up with hanging pex pipes, large joist holes that accomodate 4-6 pex tubes, etc.

Once they pex tubes are where they heat, they will be in aluminum heat transfer plates stapled to the subfloor. Nothing unusual here. I think the plates are 30 inches long or so and are of a light gauge. Aas for temperature of radiant, I'll start at what is normal for my area and see how things work.

Thanks,

Mike

[kevin]

Knowing nothing about the topic, I would think 3'' PVC is a bad idea. Imagine seing some water dripping out of that PVC. It would be a nightmare to track down the one PEX that is leaking inside the PVC, then fixing it. How about a raceway with a removable cover?

And as for drilling a huge hole in your floor joists -- this is a bad idea. Multiple smaller holes is much preferable.

[nicksanspam]

Sounds more expensive than warm air under the floor, with a few vents.

Nick

[HeatMan]

200 linear feet of PEX? That should work.

Fine. Drill holes for each run.

Why? It still sounds like you are making it too complicated.

If you drill one hole per PEX tube you should be okay.

Another question. Will you be running the circulator constantly or cycling it on and off on a call for heat?

And what is that temp?

Also, where are you getting the PEX? Does it have an oxygen barrier?

What brand and model number of circulator are you using?

There are reasons for my questions.

[HeatMan]

It is more expensive. But the comfort level is much higher.

[nicksanspam]

If the floor temp's equal in each case, would you feel the difference?

Nick

[George]

Because of the IR coming from the floor. I put underfloor hot water heat as described in when I remodeled the house and once you have it you would never go back. You feel comfortable at lower room temperatures and there is nothing like getting out of bed on a cold day and walking on a warm floor including the ceramic tile in the bathroom.

[nicksanspam]

The vents would allow some room temp adjustment.

If the floor temp's equal in each case (making the IR coming from the floor equal in each case), why would anyone feel any difference? :-)

Nick

[HeatMan]

The floor temps won't be the same. The tile floor in my bathroom is cool year 'round. When I get the RFH installed in there, I'll all but turn off the heat vents. Also, my wife will no longer complain to me about cold feet (she'll find something else to complain about)

[nicksanspam]

With no warm air beneath it? :-) If you expect say, 10 Btu/h-ft^2, that might come from an 80 F floor surface with expensive PEX and spreaders beneath or an 80 F R1 floor surface with 90 F air beneath. Upstairs, nobody would be able to feel any difference.

Nick

[HeatMan]

With radiant floor heat, you should shoot for a floor temp of no higher than

85°. Any hotter than that, it can be uncomfortable to painful.

There is a quasi-finished area underneath and the floor is cool.

I ask customers one question that I don't expect an answer to. "What price is your comfort?"

[nicksanspam]

So? You might say the same for warm air under the floor.

If you can put pex and plates under the floor, you can put warm air or fin tubes under it, no? Unless you have no faith in floor conduction :-)

A lot cheaper for exactly the same comfort, with warm air under the floor.

Nick

[HeatMan]

I never said you couldn't put fin tube or FA in the joist space. The *best* way to heat a floor is by direct contact between the subfloor and the tubing. If you don't install some kind of plates, you'll get striping. BTW, it's against every I know of to put heat from a forced air furnace into joist bays, unless the joist bays are lined with metal.

Oh, and there is a product that you can out on PEX in a joist bay that is supposed to make the raciant more efficient in a suspended application. I don't beleive it.

And you can get drafts and more hot/cool areas with FA.

[nicksanspam]

How is that *best*? :-) It is more expensive. Better for HVAC installers... The floor temp matters for comfort, but who cares how it gets to that temp?

That seems more likely with plates than warm air which can easily fill a joist cavity with a uniform temp at the top.

It's against every what you know of? It's illegal to heat a basement? :-) Warm air rises. There's no need for ducts.

Picture a Sherman tank salesman... "What price is your road safety?" Then again, that's a different situation, since tanks are safer than cars, not just more expensive.

I disagree. Especially if the A is not F'd.

Nick

[HeatMan]

installers...

What price is comfort? Who are *you* to decide what is best for your customer?

But installing plates lowers the required water temp. In a suspended application, you'd need water temps around 130° to get the floor temp to ~80°. With plates, especially the thicker alumimum ones, your water temp would need to be about 90-100°, if that high.

This is the dense part. if you heat your basement to get the heat to the first floor, that's about as inefficient as you can get. I was talking about using the joist bays as ductwork, that's against the law.

There's too many women out there that drive Suburbans and Excursions that can't easily drive something that big. Does that mean they can't? No. Besides, if you ask that question, you've been watching too many cartoons.

Then how will you efficiently heat an area using air as the heat transfer medium with out using some method of force?

Nick, either you are a troll or simply enjoy an argument. I don't have time for this.

Consider this my last reply to you on this topic.

[nicksanspam]

You might read the question above a few more times.

Were this not your last communique', I might ask how many Btu/h-ft^2 you want to get from your warm floor with the expensive pex and spreaders, with what water temp, and then figure out an equivalent and dramatically cheaper system with warm air under the floor.

You might read the sentence above a few more times.

OK. How is it *best*...? :-)

Think *equal comfort*, an equal floor temp at a lower price...

Compared to what? How about warm air under the floor?

Are you talking festoons of bare PEX in the air? :-)

Floors are reasonably good heat conductors. An 80 F R1 floor with an R1 airfilm resistance to 70 F room air above moves 10 Btu/h-ft^2, no? So it only needs 90 f air beneath. Here's a diagram:

80 F R1 | R1 T -----www-----*-----www----- 70 F

What's T? :-)

You could simply use 90 F air under the floor...

Warm air rises. We don't have to heat the whole basement. Just the ceiling.

Warm air rises.

Nick