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Concrete overpour and radiant heating?


perchking

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23 hours ago, perchking said:

I do have footings, we may just pull the entire thing up and start from scratch.  I am worried about the settling that others are talking about. 

 

That might be your best move if you want your new place to be as perfect as possible.  If you go with the in-floor heat, it's well worth your time and money to work with someone who specializes in it.  The details will make or break the performance of your system so people who don't understand or care about those details should be avoided.

 

If your new construction is going result in an air tight building like most modern construction is, make sure you check into an air exchanger.  You have to move air somehow to avoid moisture problems and mold.  Maybe you already know this; I just thought I'd add it in case.

 

Good luck with the new place.

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I am by far no expert but what I am wondering here is why not simply build a false floor above the existing concrete?  If you are sure you want to to with in-floor heat couldn't you put down a layer of insulation, maybe an inch of the properly rated material for a floor, and then build a 2x3 frame over that with the piping, and cover it will plywood.  That seem to me to be simpler and you avoid all of the risks that have been mentioned so far.  It has to be cheaper than removing the existing slab and maybe even less that the 2 inch layer you are writing about.

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1 hour ago, Tom7227 said:

I am by far no expert but what I am wondering here is why not simply build a false floor above the existing concrete?  If you are sure you want to to with in-floor heat couldn't you put down a layer of insulation, maybe an inch of the properly rated material for a floor, and then build a 2x3 frame over that with the piping, and cover it will plywood.  That seem to me to be simpler and you avoid all of the risks that have been mentioned so far.  It has to be cheaper than removing the existing slab and maybe even less that the 2 inch layer you are writing about.

True. But a few considerations. One-time he talked about expanding the footprint and if so, then this idea would complicate that process and likely make it more costly.

 

If keeping the footprint the same,he would want to put the 2x4 framing first and then put the insulation between. You don't want to put all the weight on the insulation because it can't support the load. The lumber would need to be treated due to direct contact with concrete and the slab would need to be flat and level. Also, 2x3 or 2x4 might not meet codes as you are essentially using them as joists. 

 

I can't guarantee it but I also believe the radiant system would perform better in a slab than it would if installed in framing resting in the slab  I could be wrong though.

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9 minutes ago, PurpleFloyd said:

 

 

I can't guarantee it but I also believe the radiant system would perform better in a slab than it would if installed in framing resting in the slab  I could be wrong though.

 

You're not wrong. :)

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2 hours ago, Big Dave2 said:

Is it possible to install an in-floor heat system in a cabin with no electricity?

 

The first hot water heating systems were gravity flow with no pump, so yes, it's probably possible if you had an idea of how to design a system with the proper pipe sizings, etc.  Might be tough to find someone with knowledge of how to design this type of system today, however...

 

 

 

 

 

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15 minutes ago, swamptiger said:

 

The first hot water heating systems were gravity flow with no pump, so yes, it's probably possible if you had an idea of how to design a system with the proper pipe sizings, etc.  Might be tough to find someone with knowledge of how to design this type of system today, however...

 

 

 

 

 

These are pretty common in saunas and newer camps in the UP. Any wood stove would need to run  add a water jacket and glycol for the liquid and you are golden. I built my camp 10 years ago, I wish I would have done it but but I was too cheap at the time.

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2 minutes ago, perchking said:

These are pretty common in saunas and newer camps in the UP. Any wood stove would need to run  add a water jacket and glycol for the liquid and you are golden. I built my camp 10 years ago, I wish I would have done it but but I was too cheap at the time.

 

Yes, I think some of the solar water heating systems are run by gravity, as well.  Not sure exactly how they go about controlling the temperature in the pipes, but I remember seeing some pretty cool mechanical thermostats made with bi-metal springs, so I'm sure it can be done.

 

 

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19 minutes ago, swamptiger said:

 

Yes, I think some of the solar water heating systems are run by gravity, as well.  Not sure exactly how they go about controlling the temperature in the pipes, but I remember seeing some pretty cool mechanical thermostats made with bi-metal springs, so I'm sure it can be done.

 

 

You don't in a camp or a sauna, at least the ones I've been in. It's either HOT or NOT:)

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15 minutes ago, perchking said:

You don't in a camp or a sauna, at least the ones I've been in. It's either HOT or NOT:)

 

Here's one.  This one is just a mechanical valve that senses room temperature, and opens or closes a valve in the pipe.

 

58e04489735ee_mechanicalthermostat.gif.1727092e22cb2dfa8adcdd13f4c30c1e.gif

 

 

 

These devices sense the air temperature in each room and modulate the flow of water through the radiator. They're completely self-contained and need no electrical wiring. They last for years, are relatively inexpensive and have been around since the 1920s. I've found they keep the room temperature within one or two degrees F of the set point. With thermostatic radiator valves, every room becomes its own zone.

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2 hours ago, swamptiger said:

 

Here's one.  This one is just a mechanical valve that senses room temperature, and opens or closes a valve in the pipe.

 

58e04489735ee_mechanicalthermostat.gif.1727092e22cb2dfa8adcdd13f4c30c1e.gif

 

 

 

These devices sense the air temperature in each room and modulate the flow of water through the radiator. They're completely self-contained and need no electrical wiring. They last for years, are relatively inexpensive and have been around since the 1920s. I've found they keep the room temperature within one or two degrees F of the set point. With thermostatic radiator valves, every room becomes its own zone.

That can run in a gravity system with no power source to pump water through it? Interesting. I would love to see a schematic for how they work.

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5 minutes ago, PurpleFloyd said:

That can run in a gravity system with no power source to pump water through it? Interesting. I would love to see a schematic for how they work.

 

It just works from room temperature, so when it closes the water would go into a different loop.  It's all in the plumbing.

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OK

 

So you are talking about the gravity heating systems that run water/steam like I had in my first apartment where the pipes go to radiators.

 

I think we are talking 2 different concepts though. Those gravity systems are designed with the boiler at the lowest level. They heat the water or steam and it rises through the supply line, goes through the radiators above, and then it leaves the other end of the radiator at a lower temp and back down to the boiler to be reheated.

 

But we are talking a slab. There is more than likely no practical way to install the heat source lower than the slab in order for the gravity concept to work. You could possibly try to run the pex in the ceiling and get the right effect but then since heat rises you would have very uneven temps between the floor and ceiling. 

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24 minutes ago, PurpleFloyd said:

OK

 

So you are talking about the gravity heating systems that run water/steam like I had in my first apartment where the pipes go to radiators.

 

I think we are talking 2 different concepts though. Those gravity systems are designed with the boiler at the lowest level. They heat the water or steam and it rises through the supply line, goes through the radiators above, and then it leaves the other end of the radiator at a lower temp and back down to the boiler to be reheated.

 

But we are talking a slab. There is more than likely no practical way to install the heat source lower than the slab in order for the gravity concept to work. You could possibly try to run the pex in the ceiling and get the right effect but then since heat rises you would have very uneven temps between the floor and ceiling. 

 

Yeah, I thought about that.  But all you would need to do is install an expansion tank in the attic to overcome the pressure.

 

The loops could be fed from the return side of the tank.

 

 

Edited by swamptiger
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The expansion tank wouldn't even have to go in the attic - just at a higher level than the boiler.  The principle involved is the thermosyphon effect.

 

Here's how it's done in a solar gravity feed system.

 

Thermosiphon.jpg.1768c76d987b16a6e84885a40ca3b8fd.jpg

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9 hours ago, swamptiger said:

The expansion tank wouldn't even have to go in the attic - just at a higher level than the boiler.  The principle involved is the thermosyphon effect.

 

Here's how it's done in a solar gravity feed system.

 

Thermosiphon.jpg.1768c76d987b16a6e84885a40ca3b8fd.jpg

That's pretty cool but I still don't see it as an option for a slab. Look at the red and blue on your image and think of where they are at in relation to a slab of concrete. It would probably work ok for radiators or heat exchangers with a fan and ducts but with radiant you want the hottest water to be in the slab and by the nature of that design you will have the coldest water there instead. 

 

This is why for practical reasons you need a pump for slab based radiant systems. It's not that it can't be done, but it's the most logical, most efficient way to do it. If you are talking radiators, heat exchangers etc then your options open up a bit wider. 

 

Sorry to divert the topic. 

If it's in the budget and if you don't need to keep the pad for zoning or permit/code reasons then IMHO you will get the best performance from the system if you start from scratch and built it to take full advantage of it's features.

Otoh doing radiant heat is a much higher option than conventional systems and you need to do calculations to see whether it can pay you back over a reasonable time period. Especially if it's a seasonal place which in most cases never would.

 

When we built our towns new fire/city hall when I was Mayor, we wanted to do in floor heat but the cost differential was something like 18-20k. After looking at projected utility costs we decided the payback was too long for a small town with limited funds so we went another direction and used forced air and SIPS panels for the walls which increased the r value at a much lower cost and that has given us a very efficient system. 

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As part of what might be a unique exercise here I went back and re-read the original post.  In doing so I came up with another avenue for discussion.

 

The project involves a cabin.  As in 'I'm not there all the time.'

 

What amount of time will it take if it is 40 degrees outside to get the building to a comfortable temperature inside?

 

I can remember going to the deer shack and getting a fire going full bore in the stove and then spending at least a half hour before you could take your coat off.  And that was a bunch of guys who weren't all that fussy.

 

What's momma gonna say if it takes a hour to be able to have a sit down?

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26 minutes ago, PurpleFloyd said:

That's pretty cool but I still don't see it as an option for a slab. Look at the red and blue on your image and think of where they are at in relation to a slab of concrete. It would probably work ok for radiators or heat exchangers with a fan and ducts but with radiant you want the hottest water to be in the slab and by the nature of that design you will have the coldest water there instead. 

 

You don't see it - that doesn't mean it wouldn't work.  The pipes in the slab are the radiator, and the hottest water doesn't need to be in the radiator since the system just operates on a temperature differential.  This is what I meant when I said you would probably have trouble finding someone with the knowledge to design such a system, since it is mostly forgotten technology, and most techs are trained to work with systems presently in use.

 

Here is another diagram of a passive system with a hot water electric heater tied in - the water heater could be fired by gas or other fuel.

 

Thermo10.thumb.jpg.a8333a07238b42fdef36dce5d1425583.jpg

 

 

 

Sorry to throw the thread off track.  

 

 

 

 

Edited by swamptiger
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55 minutes ago, swamptiger said:

 

You don't see it - that doesn't mean it wouldn't work.  The pipes in the slab are the radiator, and the hottest water doesn't need to be in the radiator since the system just operates on a temperature differential.  This is what I meant when I said you would probably have trouble finding someone with the knowledge to design such a system, since it is mostly forgotten technology, and most techs are trained to work with systems presently in use.

 

Here is another diagram of a passive system with a hot water electric heater tied in - the water heater could be fired by gas or other fuel.

 

Thermo10.thumb.jpg.a8333a07238b42fdef36dce5d1425583.jpg

 

 

 

Sorry to throw the thread off track.  

 

 

 

 

My reply didn't say it couldn't be done, only that it would not be practical or using it in it's most efficient manner thereby justifying the cost of doing it vs a more traditional method. While the hottest water doesn't need to be in the slab for your example to be able to circulate water through the system, logic and common sense tells you the hottest water isn't in the slab where you want the heat. Instead, what needs to happen is that the water supplying the slab needs to cool off enough to be able to return to the lowest level through your gravity concept. To do this the best heat is bled off into the surroundings until it reaches a low enough temp to allow circulation to occur naturally. This is why I said it's really not an option. Not that it's not possible to circulate water through a slab, but that the end result is not efficient and a good fit for what you are trying to do. This is why you use pumps in slabs and applications where the system operates on a single or low plane. If you want to spend all your time engineering then yeah, you can use windmills, solar etc but then get batteries and size it to use a pump to move the water:grin:

 

I think Tom pretty much nailed it and got to what my last post eluded to. In the end the juice needs to be worth the squeeze.;)

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Perchking might be willing to keep the heat on over the winter, just turned down when he's not there.  

 

I agree, Tom is right, if you're just going for the weekend and aren't leaving the heat on, forced air should be the only serious option.

 

The other thing to consider with in floor heat is your floor finish.  Tile is the best to not impede the heat transfer.  Carpet is about the worst.  So consider that as well.

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56 minutes ago, PurpleFloyd said:

I think Tom pretty much nailed it and got to what my last post eluded to. In the end the juice needs to be worth the squeeze.;)

 

The question Dave asked was whether it was possible.  Possible, yes.  Practical, economical, or feasible is another question.

 

The intended usage dictates a lot on what works the best.  If it's a weekend cabin, and it takes a day to heat up the slab, and another day to cool it off, it's probably not a practical solution.

 

 

 

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5 minutes ago, swamptiger said:

 

The question Dave asked was whether it was possible.  Possible, yes.  Practical, economical, or feasible is another question.

 

Yes.It's possible to install one in an F150, your backyard garden or a jumbo jet if you are so inclined :grin:

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OK, sorry I derailed this topic. Sounds like PK does have a power source so let's get back to Perchking's question now. 

 

Tom's comment is a good one and something I was thinking about as well. 

 

Would Perchking have to keep the cabin at comfortable temps all winter long? How fast will a system like this recover if left at a low temp like between 40-50 degrees? Even if augmented by a wood stove to heat it up once you arrive, would the temp of the in floor system recover from say 45 degrees to say 68 degrees in 2 days? If not, maybe Perchking plans on leaving the in floor system at a low temp all winter just to keep the cabin from freezing and supplementing with some other heat source? 

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