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Old 12-14-2009, 09:24 PM   #1
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DIY floor heating


I noticed when I walk on my floor where the furnace is, or where a duct passes by, I can feel a bit of heat. I've also heard of pex underfloor heating. Putting two and two together, I had an idea, wondering if it would work:

Basically run tons of pex along the floor joists going back and forth, then have it hook up to a water reservoir/heater and have a pump. Perhaps this heater could simply be a 500w oil filled heater with the tubing put all around it so it heats up (preferably use copper at that point) and the whole unit enclosed and set not too high. Think this would actually heat the floor? To make this work even better insulation could be added over the pipe but since heat rises, probably not needed. For faster heating maybe just a regular ceramic heater stuffed in an enclosed cavity where the tubing passes by.

Since too long of a run would maybe result in too much heat loss by the time the tube gets back, one single run per joist cavity would maybe be needed. I find my kitchen gets pretty cold and it takes a while to warm it up with the furnace, so I was thinking a system like this would be pretty neat as it's a more equal heat.

Think something like this would actually work? Guessing that's basically how underfloor pex heating works, but do they actually require way more wattage?

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Old 12-14-2009, 10:02 PM   #2
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I have never used them before, but hear good things. I have lurked around their site for research.
You may want to check them out:
http://www.radiantec.com/index.php

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Old 12-14-2009, 10:11 PM   #3
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You wouldn't notice 500 watts.

Staple up systems are common. But you would need more heater then you think.
The wood of the floor itself absorbs heat before it gives off heat. Along with the joist.

Some people have used regular water heaters as the source of heat
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Old 12-14-2009, 10:34 PM   #4
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My radiant floor system is rated at close to 15w per sq ft for my bathroom
This is what they say to use for cold areas, no heat or on a slab
12w per sq ft is what is rated for areas already being heated
10w for lower heat loss areas
Measure your area & see what you would need
In addition electric is usually the highest cost for heating
Unless you have a good rate due to hydro ?

Without it being in a tile floor system you will have heat loss & the plywood will slow down the heat transfer
You would probably need to leave it running all the time to have any effect
Best bet would just put the oil filled radiator in the room

We use one for our son's bedroom, 600/900/1500w settings
At 600 it keeps it warm - under 70, 900 really warm - 70 or over
1500 warms the room up pretty quickly

I looked into the staple up radiant electric heat
I've insulated the basement & sill area, replaced basement windows & doors & sealed cracks
Basement usually stays above 60 which keeps the kitchen warmer

An ounce of prevention is worth a pound of cure
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Old 12-15-2009, 06:55 AM   #5
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Quote:
Perhaps this heater could simply be a 500w oil filled heater with the tubing put all around it so it heats up (preferably use copper at that point) and the whole unit enclosed and set not too high. Think this would actually heat the floor? To make this work even better insulation could be added over the pipe but since heat rises, probably not needed. For faster heating maybe just a regular ceramic heater stuffed in an enclosed cavity where the tubing passes by.

Since too long of a run would maybe result in too much heat loss by the time the tube gets back, one single run per joist cavity would maybe be needed. I find my kitchen gets pretty cold and it takes a while to warm it up with the furnace, so I was thinking a system like this would be pretty neat as it's a more equal heat.
Ayuh,.. Sounds like you're trying to Reinvent the Wheel,... rather Inefficiently at that...
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Old 12-15-2009, 11:25 AM   #6
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DIY floor heating


Hmm so guess it would not really work that well then. I thought I'd check before I go ahead and try to do it. It seemed too good to be true. Suppose if I left the heater run 24/7 it would work to some extent, but then may as well just keep the furnace up a bit higher for same cost or put the oil filled heater in that room like mentioned. I should have went with undertile heating before the tiles were put in.

I'm toying with different ideas to recycle server room heat once I build my server room, so I might do it with that given the server room is nearby. Even if it's very minimal it's heat that would otherwise be wasted anyway. Though it may be more efficient to just pump that heat directly where I want it.
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Old 12-15-2009, 04:22 PM   #7
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Just checked for kicks and the area I would want to heat (no point in heating under the cabinets and such) including my entrance is about 142sft which comes up to these potential wattage requirements:

142 * 10w = 1420w
142 * 12w = 1704w
142 * 15w = 2130w

Since this would be secondary heat, and assuming my heat loss may not be that much I could probably get away with either 10w or 12w per square feet, but if I was to go ahead may as well go for the gold, and crank that up to 2kw. That's a lot of power though, probably not cost efficient to do this unless I went gas. :P

Just out of curiosity though, for those that have a professional install, how long does it take to start feeling the heat? I'm guessing it takes a while for the heat to transfer through all the layers. My parents have an electric heat pad in the washroom downstairs and for it to be effective it pretty much had to be on non stop, it took like 12 hours for it to actually warm up if it was turned off for long then turned back on.

Also pex alone is probably not enough to transfer heat is it? Probably need to keep alternating between copper and pex along the lines, and have a foil/copper plate attached to the pipe?
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Old 12-15-2009, 04:28 PM   #8
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Radiant heat can't be used as a secondary source of heat. It has to be used as the primary. Radiant floor heat is slow.
Pex is fine as a heat transmitter.
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Old 12-15-2009, 04:43 PM   #9
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I don't see why it can't be used as a secondary heat source
We heat our house to 68, cycles between 67-69
Bathroom radiant floor is set to 65 most of the time
--this extends out to the hallway between bedrooms/bathroom & then just a few runs down a long hallway
Morning its up to about 70 when the wife takes a shower
When we give our son a bath we turn it up to 73
If we have the heat really low (gone for the day) I will turn it up to 70 when we get home until the radiators get up to heat

Heating from underneath it could take over an hour for the heat to come thru
Someone installed it on top of cement pad, then tiled
They had to leave it running 24x7...if the pad cooled off it would take 1/2 a day to heat up
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Old 12-15-2009, 05:05 PM   #10
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Your thermostat must be off. If you set it to 65, and it heats to 70.
Which would then make it a primary heat source.
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Old 12-15-2009, 05:23 PM   #11
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DIY floor heating


Hmm I see what you're saying, so the floor heat would make the main thermostat go off, then the rest of the house would be too cold, or the furnace would keep cycling on/off.

What about a situation like this, where the main thermostat is on an opposite wall and I only want to heat a specific location? Black = wall, gray = cabinet/area that I wont heat.

If I did do this it would probably be controlled by a timer either setup downstairs or on the wall. Would probably have to get into a 240V source of heat, maybe a tank less heater system? do those have built in thermostat to avoid overheating water? Eventually the water would reach a temp where it can probably shut off for a bit while it keeps circulating. The timer/thermostat would control the heater and the pump. Idealy the pump would run for a bit longer then the heater.
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Old 12-15-2009, 05:46 PM   #12
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Quote:
Originally Posted by beenthere View Post
Your thermostat must be off. If you set it to 65, and it heats to 70.
Which would then make it a primary heat source.
Programmable thermostat
No sense heating the whole house to 70 just to heat the bathroom to 70
My house thermostat isn't near the bathroom, so very little effect
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Old 12-15-2009, 06:51 PM   #13
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I have radiants hooked up. That use the radiant as first stage heat. And then when it can't handle the load anymore, the thermostat brings on the hydro air handlers, and cycles them off and on. All off of one 2 stage thermostat.

Only way radiant can heat up quick. Is if it is oversized for the area. Which only has a minor draw back of over shooting sometimes on mild days.
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Old 12-15-2009, 06:54 PM   #14
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Red.

For your description/area. A 2 stage thermostat. First stage brings on the radiant. Second brings on your normal heat. Use a floor temp sensor to control the radiant floor temp.

That way. If you go away for a weekend. You only have one thermostat to mess with. And can use vacation feature to bring the temp back up before you come back home.
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Old 12-16-2009, 01:01 AM   #15
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DIY floor heating


Hi there is no reason why it wouldn't work afterall that is all underfloor heating is.

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