To get rid of an old radiator in a kitchen, I am considering countersinking a RFH system between full 2″x full 10″ joists, spaced 16″ O.C. with the pex 8″ O.C. and on top of 1″ thick ply, resting on 7-8″ of 1″ ply, bonded / screwed to and sandwiching each of the joists from the bottom of each, up to the level of the counter sunk sub floor.
How much concrete should go underneath the pex – and how much on top ?
How much OVER the tops of the joists as a bed for the tiles ? Any particular product recommendations ?
Has anyone else done this successfully ?
Does the contraction / expansion cause the floor on top to crack ?
Floor area affected is about 7′ by 10′ – should I use some form of expansion membrane over top of each joist ?
What kind of reinforcing in the concrete ?
Anything else I have neglected to think of ?
Gavin Pitchford
Replies
are you going to get enough heat out of a 7'x10' area?
bobl Volo Non Voleo Joe's BT Forum cheat sheet
Small kitchen - 9 x 11 - replacing a small rad 28" - kitchen is fully open to large dining room which has 2 larger rads. 26X40 Window being replaced with hi e glass, both rooms to be insulated with poured foam, over heated basement. 9'10" ceilings...
Some advice would be good on this score, actually - The kitchen will have counters and cupboards along the exterior walls (makes exposed floor heating area 7X9) and I don't think I want to heat the pots and pans and cans of food under the counters, do I ?
Do you think the RFH area is too small for the room ? Gavin Pitchford
I have similer sized kitchen 10x12 w/7.5' ceilings, includes counters
had a RH quy come out
said not enough floor space/
bobl Volo Non Voleo Joe's BT Forum cheat sheet
Edited 4/2/2003 4:45:03 PM ET by bobl
So any other thoughts about how to get rid of the rad and heat the space - the rad has to go ! Electricity is too expensive.Gavin Pitchford
radient heat can be put into the walls and ceiling.bobl Volo Non Voleo Joe's BT Forum cheat sheet
open plan - walls - except for one 4' section - are exterior and behind cabinets - and full of icynene.
Ceiling is 10' - not much heat going to "fall" down.Gavin Pitchford
Put your pex on top of your floor ply and pour a 1 1/2'" concrete layer on top,put some metal lathe down first.I've done this and it works great.As far as I'm concerned no area is too small , the concrete will give some thermal mass and it feels great on the feet.Make sure you insulate between joists below.
Gyros
Thanks for the feed back: will 2X10s take the load ?
How much concrete under the pex ?
reinforcement in the concrete needed (other than the mesh?)Gavin Pitchford
2x10 will take approx. 45 lbs/sq.ft depending on span .1 1/2 " reg. concrete will add about 17 lbs/sq.ft.Staple your lathe right to the floor with some electrical wire staples then lay pex right on top in pattern of your choice fastening to the lathe or the floor depending on fastener.Wirsbo recommends min.5/8 conrete over tubing so count on about 11/2"to 2" of concrete on top of all.Great for leveling older and uneven floors.Don't forget to insulate under the floor to keep heat from transfering down.I have about 1400 sq. ft. done this way in the older part of my home plus another 1000 with slab on grade with 5" slab then my upper level is another 1400 with tubing under the subfloor on the second level,hardwood on top so I've done them all it just depends on what you have to work with.
why insluate under the floor when heat rises, seems like a waste. use the cash from insluating and put up a couple of celing fans for thoes 10' rooms.
The logic I've heard from the RH guys and texts is:
Heat doesn't rise - warm air does. Heat radiates in all directions and as such you need to provide some directional guidance to get it where you want it.
As I said, that's the reasoning I've heard.
KW
Radiation isn't the same as convection. Radiant heat doesn't behave the same way as forced air. It transfers in all directions through the path of least resistance. If you don't insulate underneath RFH, some of the heat will transfer underneath. This has to be accounted for in calculating the btu's you expect to apply to each room.
To all,
Many thanks for all of the information. It's been great to have so many fine minds engaged in helping out and much appreciated.
Any special concrete mix suggestions ?
Any worries about the concrete cracking over top of the joists where it will be thinner ? Do I need expansion joints between the joists and the concrete ?
Thanks
Gavin Pitchford
warm pots and pans will heat up your kitchen to.
Have you considered using the electric floor heating nets. I've not used them but they appear to be able to be installed in almost a standard tile floor bed of mastic. This might simplfy everything for such a small area.