New system started up need a few ideas

Joebif

I have a radiant system in my Utility room

running today, (First snow fall and cold) and have got the Propane

heater set at 120 degrees. I have a variable speed pump running and set

at a DELTAT of about 5 degrees. I can see the supply temperature going

out at 120 and the return at 115 but the room is taking a long time to

warm up.





Granted it is not perfectly tight, but will be soon, and was

wondering why it is taking so long. The room has 5/8" pex on 12" centers

under 1-1/4" of OSB and plywood. I am going to set the water heater to

140 and see if that makes a difference and warms it up quicker.



I do not want to run the water heater to hot but not sure.  I do not

think that the OSB and plywood floor will have a problem getting too

hot, it is not like a hardwood floor. The room has 3 loops at about 120' each.





Any thoughts?

Mark Eatherton

S L O W recovery...

Joe, High mass radiant systems like yours take an extremely long time to get up to speed. Kind of like push starting a train. It takes a LOT of energy to get it moving, and once moving, it takes a long time to stop it as well.



Attempting to accelerate the slabs recovery will result in significant discomfort and overshoot. As I tell all of my high mass radiant customers, start low and go up slow, like set it at 60 degrees F and then turn it up 2 degrees F per day until you hit the comfort zone, and then consider turning it back a degree or two and see how you like it.



Patience is a virtue when it comes to high mass radiant. Hence, it may not be for every job (i.e. weekend use mountain home that is idled cold when unoccupied.)



ME

Joebif

I understand

I did not know that it would take that long.  I will keep it back down to the low setting on the water heater.

Jean-David Beyer

The virtue of patience.

I have radiant in a slab, too. I find if I change my thermostat setting (e.g., to request more heat), it takes about 4 hours to notice anything, and the whole system takes nearly 24 hours to stabilize. YMWV.  What I have found is that I should not use any setback because it takes way too long to take effect. I also have outdoor reset that is adjusted to supply barely more than what is needed (I am talking within 1F of what is needed). So my radiant zone runs between 75F and 120F, with design day at 112F.



I use setback only for vacations, where I turn the temperature down from 69F to 60F. I have a fancy thermostat and set it to turn the heat back up about 24 hours before I return. That can save money, especially if I am away for a week or more. But the finances have reduced my vacation taking.



My other zone is baseboard and I could use setback there, but my reset curves are so close that  If the setback ends, it still takes a very long time to heat up because the boiler is supplying only enough heat to maintain the setting, not to recover from the setback. With extreme outdoor reset, using much more than a degree of setback (except for vacations) does not seem to make sense.

hot_rod

Lots of r-value

1-1/4" of floor is about a r-1.4. You may need 140F or more to drive through that much resistance. Is the tube installed in heat transfer plates?



The heatload design will determine how many btu/ ft that room needs. And a radiant design simulation would tell you what temperatures you need to supply to get the needed output.



hr

Joebif

After one day

I started it out at 120 then went to 140.  I got it up to 65 and thought that was good enough.  I then set it back to 120 and set the temp to 60 and left for the morning.  Just got back and it went down to 64 so it looks like it is working like I wanted it too.  I will keep it that for a while.  Now I have to wait until it gets real cold out.