radiant under floor joists

woodworker88

I am having a problem getting heat transfer in my floor joist application.  What temp should be run in this application?

pipe4zen

floor joists

We need to know:

1) Heat loss of the rooms above. Was a load calculation done?

2) R-values of flooring, hardwood, tile, carpet.

3) Was heat transfer plates used?

4) Was Insulation used between joists?



Knowing those design comsiderations, will give you water supply temperatures at your design day conditions.

Gordy

I hope

You mean radiant between the floor joist, and not under them.

woodworker88

response

I have 1- 7/8 pex line per bay with transfer plates and reflective insulation under that.  Laminate and Tile above.

Gordy

Combined posts

I see you also posted in another thread. You are running 140* supply with 85* return. Using 400' 7/8" pex loops with one run in each joist bay. Heat transfer plates used.  Reflective insulation only. 15-58 circ, and takagi jr. instantaneous water heater.  Are the details correct?



Gordy

woodworker88

reply

That was for my concrete.  Under the unstairs floor is approx a single 240 foot run with the takagi jr and 15-58 pump with transfer plates and reflective insulation.  It seems like as it is running I don't get heat transfer but if I run it for awhile then shut it off after it shuts off It will get a couple of degrees higher but if I leave it running it won't get any higher

Gordy

Specifics

As stated above.

 what is the size of that pex... O2 barrior?

What is the R Value of the flooring?

What is the heatloss of the space you are trying to heat?

You stated you have plates, and that it is staple up.

Pics of the Takagi jr setup would be nice. Needs Primary secondary pumping. ( 2 Circs) one for the Water heater, and one for the emmiter. High head through the tankless= Low flow through the emmiter with one pump.

 Warming after wystem is shut down is probably lack of flow check, or one properly placed.



Need more insulation than bubble foil in joist bays also bubble foil won't cut the mustard alone.



Bottom line you need the heat loss done. This dictates tubing lay out water temps, and flow rate to deliver the btus needed to heat the space.



Gordy

woodworker88

reply

Any way to get a schematic of the way primary and secondary pumps should be hooked up with the Takagi Jr.  the pex is 7/8.  not sure of the r value of the flooring.  The room is new construction with R19 sidewalls and R30 in the ceiling

Mark Eatherton

Just guessing here...

Sounds like you got one of them there internet radiant heating systems...



Tubing 16" O.C. isn't going to deliver much more than "floor conditioning", which means it may knock the chill off of the floor, but not much more.



What does the company who provided you with the system have to say about its inability to heat your dwelling?



I agree with everything Gordy has said.



Heres a picture of the P/S piping arrangement.



Does your boiler short cycle?



BTW, the picture show is for an open system, which I do NOT promote. Death trap waiting to happen IMPO. You may need water temperatures as high as 180 degrees F to push heat through the floor, but your supplier should be able to tell you for sure.





ME

Gordan

Yeah, 7/8" PEX is a dead giveaway

It's atrocious what can be found out there, both online and offline.

Gordy

Big Bore Pex, and one run joist bays

I liken it to trying to heat a home with 16" dia pex run through the center of the house. Every one is sweating in the center of the house, and freezing near the outer rooms. Thats what is going on in the joist bay.



Gordy

SWEI

them there internet radiant heating systems...

I've seen more than a few of these posts from unsuspecting homeowners so I decided to go take a look at the probable source.  Yikes!

Paul Pollets

There oughta be a Law!!

That these systems can be sold and installed, with very little recourse to the consumer, sure shows how weak the codes and valid inspections are.