I have a concrete and block porch that has been enclosed to create a living space. So far, I have added baseboard hot water heat, pink stuff in the frame walls and ceiling, installed double pane thermal windows, and added 1-1/2" rigid foam over the 32" high brick walls. My last project is the floor. The concrete floor is covered with slate tile and is very cold. The entire room is insulated except the floor. What is the best way to insulate the concrete floor from below?

The best way to do this might be to seal any vents and insulate the crawl space walls. In that case, the crawl space must be "conditioned", which basically means heated. If there is, or could be, an opening from the crawl space into a basement, that is one way to satisfy the code. Another way is to install a unit which "steals" a small amount of conditioned air from the house, and delivers it to the crawl space. Home Care Club knows the name of this unit...I will try to find it for you.

I've tried and failed...let's hope Home Care Club sees this thread and responds.

This is the enclosed porch. It has 4 separate crawl spaces. All crawl spaces have been covered with 6 mil plastic. #1 is located to the left of the cellar door, #2 is to the right of the cellar door and under the stairs, #3 is behind the door with the vent to the right of the stairs, and #4 is behind the access door on the right. All spaces are devided by block walls and have a 4" concrete ceiling.



This the crawl space with the vented door before I installed the 6 mil plactic over the dirt. The hot water baseboard gets the room up to 68 degrees so this week I am installing rigid insulation over the brick 1/2 walls hoping to hold in more heat so that the room gets warmer without adding another baseboard.

Have you looked into radiant heat for the floor. Seeing you have hot water heat, you would simply install a pex hot water loop which is attached to the floor with aluminum channels. Then you cover over the pipes with insulation. A control would be used to lower the temp of the water entering into the pex system to around 80 degree range. This will heat the floor and the entire room.

Otherwise you can insulate the floor below but the heat loss out the side of the cement wall area cannot be controlled in any manner without insulating the outside of the walls. Which is not an option you have.

Or like Richard said you can heat the crawl space to bring it up to around 60 degree range which will help keep the floor warmer. Any more then that without complete heating of the space would be waste of energy.

last thing you can do is put down carpet on floor. You can purchase electical radiant heat elements from Lowe's and Home Depot stores (special order in some) and put them under the carpet or install them into a new bed of morter and new tile on top.

In the end the only way is to install the radiant heat system. Of course this is the most expensve method but it will work.

Radiant sounds like an option. What is the thickness limit of the slab floor above before radiant heating is not a good option. My boiler is little over sized for the house so I have plenty of BTU's to spare.

The thickness should not be a concern. What needs to be done correctly however it the insulation to cover the pipes that directs the heat to the cement. There are a lot of good web sites that will cover this.
I do suggest however that you obtain the services of a plumbing heating contractor who does this type of work. As the valve hookup can be tricky as well as setting the controls so not to overheat the room.
Its not really a do it you self project in some aspects. But if your handy you can do most of the pipe runs, and setting of the tube supports onto the cement floor.
As far as boiler size. Most boilers can handle the additon of raidant heat quite easily. As you do not heat the water to the radiant heat pipes nearly as high as you would for the baseboard units. If you did overheat the pipes the room would become overheated real quick.
You could try this web site for more info
http://www.heatinghelp.com/

Thanks for the help. I will check out the information on the web site.

Since my last post I have completed a certified solar installation course. Sometime in 2010 I plan to install 8kw of solar at 1/2 price. This will allow me to use clean electric energy to heat and cool the house and use the oil boiler as a backup system. So rather than using the radiant heating under the family room floor would I gain any benefit from just insulating the ceiling of the open door crawlspaces shown above? I know I will still have a thermal break problem but I have eneough 2" rigid form to cover the ceilings should that the floor will stop pulling heat out of the room. Will this approach help keep the floor a little warmer?

Thanks