In floor radiant max temp?

Timco

So I have a system with 3/4 pex (orange) from the mid 90's. Large house, modern, all cement & glass walls. Zones will not make setpoint (or even close) at 15* nights. I am going to adjust my curve and check pump speed tomorrow but what is the max water temp I can run through a pex in cement system? Floors are like 2" thick, pex is in there somewhere! No details were given on that end, I just know what's in the boiler room, and it ain't pretty. Have to run to grand-daughter's piano recital this very second or I would give more boiler room details.....



Merry Christmas!!



Tim

Gary P

In floor Radiant Max temp

For Starters here are some numbers



With no covering on top of the concrete, ( rugs, wood floors etc.)

110 degrees will provide 24 BTU/ Square foot.

120 will provide 28 BTU / square foot of floor.



I usually go with 110 in concrete, if it is not keeping up go to 120.



Check your temperature drop across the heating circuit, water temp into floor, water temp out of floor. should be 10 or lower for radiant. If 20 or higher, circulator is to small.

Timco

pump, other info

Pump is a 26-99 3-speed. Just the single loop of 3/4. Right now, the Tek 403 is set to 120 max, which allows the mix design to reach 130 but that is still far short. Cust swears they ran 150 in there, but I never saw that. Also, on mild days, the system is waaaaaaaay oversized and sounds like a jet taking off so they moved the pump speeds to low to get rid of noise, but I just stopped by quickly last night while the owner was in town and did not have my truck. I head back later today.



Is there a "max temp" that should be run through concrete? What happens when that is exceeded?



I am working on sizing a coil (or two) to add onto the AC air handler and run some hydro-air off of a 2-stage stat that would deliver 100k btus to the areas that need it on the main floor, since duct work is there now.

Dave H_2

Radiant water temps

In a slab, max water temp is 140-150 depending upon the mix, however, with that temp get ready for undershooting and overshooting of the room temp as the slab flywheels with temp.

In order to figure it out, a heat loss needs to be done.....to size the pump and the water temp needed.

Floor coverings, tube spacing in the slab, room size, total length of the tubing are also things needed.

What control strategy is used to control the water temp for the slab and is the zone pump after the mix device?

Alan (California Radiant) Forbes

A Grandad?

I thought you were like, 25 years old.



I had a job just like yours only the radiant tubing was copper and it seems the original installer messed up by too wide a spacing on his tubing. It had an old Peerless boiler doing the work at a 180F setpoint.



That was the highest temperature I've ever seen going into a slab.

Gary P

Radiant temp reply

Try to set the curve for



130 on a 10 degree day and 90 at 60 degree day.



Thank my help balance it out. Also make sure the thermostat is configured correctly. Heat anticipator settings.



I have a friend that did there own system and there is no mix temp, they run 180 through the floor. I do not recommend this but it it possible.

Timco

Grand kids!

Nope, I'm 41. Both of my kids are early 20's and no children, which is a good thing for each of them.



My wife has 6 grown children who are 10-15 years older than my kids. 12 grand kids from her side!

Jean-David Beyer

Try to set the curve for ...

YMMV sure applies.



My radiant slab currently gets 76F supply water if the outdoor temperature is 50F and above, and it gets 120F if it is 6F or below outside. I have never seen 0F outside. 14F is design temperature around here (New Jersey), and I have seen it get below 9F for an hour or so a couple of times in the last four years.



Those temperatures were arrived at by carefully setting the reset curves until the circulator for that zone ran almost constantly.

AirborneTrav

Loop size?

In your 2nd post, you say "just the single loop of 3/4". How many zones are we talking here and how many square feet are you trying to heat? Do you know if the system ever behaved properly? It seems possible that your loop or loops could be too long. A properly designed system should be able to easily heat a concrete slab at 110 or 120, even in design days, unless there is some ridiculous amount of heat loss going on somewhere. I definitely agree with Gary P- take accurate readings of your supply and return temps. If you have more than a 15 degree difference, either your pump isn't big enough, your loop is too long, or both. Also, a second stage HWFC will help get near set point, but for max comfort, you want the customer to be able to rely on the radiant as much as possible without having to run the air as well.

jumper

bad side of radiant floors

Cold nights your heating system is busy warming the underside of your bed. Buy some electric blankets. Insulating curtains can help too.