Replacing bathroom radiator with "in-floor" heating

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Old 06-19-11, 07:44 PM
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Replacing bathroom radiator with "in-floor" heating

I've started looking into this and I have to wonder if it's really as complicated or even worth it. I('m putting a new tile floor over the old tile (which sits in 2.5" of concrete) and was hoping to put some radiant in-floor heating in. Can someone point me in the right direction as to how to figure this out? What don't I know that I don't know? ( i know nothing. I'm a first time homeowner and never had radiant heat before this house.) If it helps it's a 100 year old two-flat in Chicago. The boiler is from the mid 60's.
 
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Old 06-19-11, 08:25 PM
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if you dont know how to run hydronic radiant don't do it. It's somewhat difficult and quite costly. If you want radiant, throw down the electric mat. Bad thing about that is the cost of running it and if its not done right your tiles will crack. this happened in my kitchen when the previous homeowner decided to put down the electric mat.
 
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Old 06-20-11, 05:45 AM
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I concur with RD... get this wrong and it's a MAJOR headache, and costly.

For starters, is the existing heat even HOT WATER? or is it perhaps STEAM?

If steam, fuggedaboutit right from the git go.

If hot water, you can't use the same high temp water that goes to the existing radiator, you need some additional controls to lower the temperature of the water circulating in the floor. For radiant you don't want more than 100 water under the floor and the existing system would be set up for something like 180. Depending on how the original piping is set up, this could get difficult and complicated.

Another question to be answered is whether or not you can get enough BTUs out of in-floor radiant to replace the output of the existing radiator.

Also, can you even afford to raise the new tile another 1/2 to 3/4 inch? You said the new tile is going over old... so your new floor is already going to be higher. Why are you going over the old tile anyway? Can't it be removed?

The electric mats that RD mentioned would be a good choice, you would need some electrical work done. If it's the cold tile floor that you want to warm a bit, this is ideal solution. Keep the original radiator (or replace with a modern panel radiator) and just use the infloor as needed when you want the floor warm.
 
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Old 06-22-11, 12:07 PM
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Underfloor heating is easy!
First of all, does your existing radiator keep the room warm on the coldest days/nights?
If it does what heat output in watts are you getting?
You will need to match or exceed that output with your underfloor heating.
You go on the net and find out, the heat output in watts per meter for 1/2 inch barrier pex, at the temperature you will be running, this tells you how much pipe to fit, you can also look up the alternative layout pattens.
To work economically you will need at least four inches of polystyrene below the concrete slab and two inches round the edges that will enclose the pex and direct the heat upwards.
To stop the concrete from cracking you will need some steel reinforcing mesh, this needs to be at least one inch above the polystyrene, so that the wet concrete flows under the mesh, the pex will be tied to the mesh to keep it in place while the concrete sets.
Without the steel reinforcement, the concrete will crack and it will also curl up.
Buy and fit a normal thermostat radiator valve to the outgoing return pipe to the boiler to control the heat input.
Note: UFH works best when its left on all the time, as it takes some time for the concrete slab to warm.
If your bathroom is large, you may need to fit another dedicated pump to drive the hot water round the pex, the flow resistance can be high.
Tiles may crack, this can be avoided by fitting a plastic membrane below the tiles and above the slab to allow the tiles to slip and expand.
 
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Old 06-22-11, 03:35 PM
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Doesn't sound "easy" to me Perry! Sounds like a lot of hard work and engineering for a homeowner that admits this:

( i know nothing. I'm a first time homeowner and never had radiant heat before this house.)
Also, if you noticed, his plan is to install ON TOP of existing tile and a 2.5" concrete PRE-EXISTING slab.

Yes, easy to say easy... but you want the guy to jack out the existing slab? No... I didn't think so.
 
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Old 06-23-11, 02:51 AM
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Yes, but he wants to learn, we all had to start somewhere, why not with a simple job like this.
 
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Old 06-23-11, 04:29 PM
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The point I was trying to make... jack hammering out an existing 2.5" slab of concrete is NOT easy! If you think it is, I do NOT want to arm wrestle with you! Next, after adding the insulation that you recommended, one must then MIX a bunch of concrete and pour the new slab after setting the tubing... and that ain't easy either, OR fun!

I understand that he wants to learn, but I don't believe he wants to fail!

If this is in fact a hot water system, he can't simply run the high temp water through the concrete anyway. He MUST temper the water down to appx 100F, and this means significant engineering needs done... there needs to be a tempering valve installed, along with the appropriate pump controls.

NOT easy!
 
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Old 06-23-11, 04:34 PM
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Here is how one would go about doing hydronic radiant in a small space

A Little Floor Warming Please<br>John Siegenthaler - Column - Plumbing and Mechanical
 
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Old 06-24-11, 03:09 AM
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Merely from a point of view.........I have installed systems like this, all be it bigger, run off the central heating hot return, just before it re-enters the furnace where the water temperature has dropped to the required level...having already been round the home.....and controlled by a thermostat and circulator/pump.....needles to say they work perfectly! Installed as outlined a small system as proposed does work.....and it avoids the expense, all be it small, of installing a temperature reduction valve and the pipework.
 
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