Replies

1. 
   calvin | Apr 10, 2015 05:53pm | #1

   Nk

   Have lived with HW heat in the slab for over 25 yrs.  much better technology and controls are available now.

   in our case, different zones with different thermostats.  A little bit of putzing around to get it right, but what you don't do is manually or program a temp setback.  Screw it, set it and forget it.  BR, if you want it 62, set it and close the door.  Layed out and figured properly it should hit that point, call for heat as necessary.  Open door connects it passively to the rest of the layout.

   our floor plan is wide open, 2story.  MBR is open to floor below, no HW heat in that room.  2remote BR's have a short length of HW basebd.  Baths upstairs have HW under tile over frame.  All own thermostats.

   Now there are controls and sensors to auto adjust things according to exterior swings.

   to me radiant must be layed out specifically for each space and its heat requirements.........carefully.

   you don't necessarily rely on it for any whim.  The mass of concrete needs courted vs. one night stand.

1. 
   Mongo | Apr 21, 2015 10:06am | #2

   agree...

   Your thought is to take a high-mass, slow-response system (RFH in a slab) and operate it as a low-mass, quick-response system (RFH staple-up or warm board type of set up).

   As Big Cal wrote, that's erroneous thinking.

   With a high-mass system, you'll suffer a bit in the in-between seasons, or when you get a few days of significant fluctuating temps.

   For example, you come out of long cold spell where the slab is loaded and you get hit with a couple of days in the 70s. The slab will be giving up it's stored heat and the room might over-temp for a bit.

   Same on the flip side. A warm fall followed by a couple of days of freezing weather? Your room might be cold for a bit while the slab comes up to temp.

   Zones help. Then as Cal wrote? For the most part, set and forget.

2. 
   Roger Anthony | May 08, 2015 02:39pm | #3

   Lightweight UFH

   Underfloor heating is perfect. My feet are planted on my own light weight UFH at this moment.

   My system is, a concrete slab, covered by six inch thick floor grade polystyrene, with pex pipe laid in the top, covered with inch thick osb, covered with a thick poly-polypropylene carpet.

   This system, is lightweight and responds quickly.

   The problem with UFH pex pipe is, heat is radiated through 360 degrees, so as much heat goes down, as goes up, you have to minimize the downward loss with a good layer of insulation.

   A first floor system, would be, a standard floor, covered with four inches of polystyrene, plus t&g OSB/floorboards as the heat would not be lost downwards,  heating the room downstairs.

   Concrete has a high heat retention level, it is very slow to heat up and even slower to cool down. Its main problem is trying to cool it down, on a typical spring or autumn morning it starts off cold outside, the heating is on, the room is comfortable, then the sun comes out, quickly the heat rises, you cannot turn the heating down - you end up opening the windows, wasting your heat and money.

   With a lightweight floor and a room thermostat controlling a motorized valve and boiler, the temperature will remain the same within half a degree.

   And yes, it is best to turn it on when you move in, leave it set at your preferred temperature, and turn it off when you move out.