Radiant Heat in Slab -- HELP!

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Hi Folks -
I live in NY where it's cold, and I have a question here that I'm literally afraid to ask. I have a contractor doing a new kitchen for me and he's almost done and has 80% of his money. The kitchen is 12'x17' and, unlike the rest of the house, sits on a slab extension out back (there's a full basement under the main footprint of the house, which is 90 years old, and this kitchen extension is an appendage off the rear).
The extension was actually pre-existing from about ten years ago when the previous owner put in a laundry room and a few walk in storage rooms there. Anyway, my goal was to have the entire area over the slab gutted (12x17) and make it our new kitchen, with ceramic tile floors, and have radiant heat.
Here's the deal... we're almost done, the contractor put in the radiant heat tubing long ago, laid the tile done weeks ago (but never hooked up the heating system to the boiler till now) and has continued to build the kitchen and is almost done with everything.
But yesterday, they finally hooked up the radiant heat to the boiler, and there is bad news. After running it for two hours at 180 degrees the damn floor is still cold... and the return water is barely luke warm!
I'm starting to worry that this whole damn thing has to be jack hammered up and redone -- an unimaginable thing given the amount of time we've been without a kitchen (my wife will not survive this if it's true!).
My question is, based on the original requirements I gave, did my contractor do everything right?
First, since the new kitchen is on the north end of the house, while radiant heat sounded like a good idea, I warned him profusely that it gets cold there... and wanted his assurance that the system he installs had plenty of power to get this space warm and keep it comfortable at a reasonable cost.
These were the steps he took --
1. The whole heating project was done by him with direction given by his "plumbing and heating guy"
2. First, he basically reframed the whole extension (12x17) because it was poorly built by a do it yourselfer, insulated it with the best new stuff, and put a new roof on top... this part seems good ... you can definitely feel that the above ground part of this kitchen extension was done right;
3. Now for the slab and heat, where I'm really worried -- first, although he was able to jack hammer away the very poor concrete laid by the previous owner, there was some incredibly hard concrete below that that made it impossible to go any more than 2 inches deep (the house probably had a patio or landing out back originally, the house is 90 years old)
4. With the slab cleared down to the 2" depth, he said "to be safe" he'd put in 50% more "tubing" than would normally be required for the space - this was to address my heating worries - and he didn't lay the tubing under the 24" cabinet perimeter. Is it correct to use 50% more tubing than is normally necessary?
5. Ok, this is what I'm horrified of - he didn't insulate the slab. Originally, he said he WOULD be putting some insulation on the slab, and then lay the tubing on top. But after it was all done, with the rest of the floor poured over it and the tile man had laid his floor and had gone -- after that -- I asked him about the insulation below, and he broke me the news -- "we couldn't put the insulation bed under the tubing because that would have raised the floor height too high -- you would have hated it."
Shocked and a bit worried about the lack of insulation on the slab, I asked him if that would affect the ability to heat up the room satisfactorily or create a heating cost issue -- he said "no, it won't be an issue, don't worry about it."
But again, since that conversation, it seems like he's been putting off getting the heat hooked up to the boiler forever, and here I am today --- with this dilemma.
Worried about the issue last night, I called him and he said he'd come over and talk about next steps with me today. He's mentioned a few things, like insulating the perimeter of the slab (outside the house), installing a stand alone water heater in the basement just for the extension heat (my 80 year old boiler, while it heats the main house fine, might no be well suited to handle this radiant area he says)... so basically, he's talking about plan B's with me now.
My question is this... is NOT insulating the slab below the heating tubes a fatal flaw ? that dooms any solution short of jack hammering the whole place and starting over?
Thanks for any assistance.
Tom
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I hope the contractor has resources so you can sue if he does not correct at his expense. Seamus J. Wilson

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Is not-insulating the slab a fatal flaw? Is it the reason for the poor heat-up? Will it cost a lot more to heat without it? He seemed to think it's a nice to have but not a have to have.
I need to know if failing to insulate a slab above which will be a floor with radiant heat is a negligent act.
Tom
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If the water going out is 180 and is barely warm coming back then I would say that it is working. This is not forced air. No instant gratification here. Keep the pump running to the floor for 24 hours, it will take some time for the slab, tile and everything to warm up. You said it was cold outside....
As for the insulation, I do not know if it makes a difference. Besides it is not like your going to jack hammer the slab up any way.
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wrote:

He says 24 hours. I say 48 hours minimum and preferably 72 hours before you even put a thermometer to it. And that might not be long enough.
In two hours, the system has not even started to stabilize. Give it 72 hours running full steam and report back to us.
PJ
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How cold is it?

How many Btu/hour?

How many gpm? What's the floor temp and the return water temp?

...2" of new concrete over 6" of old concrete over soil or stone might be 8"/12"x12'x17' = 136 ft^3 with 25x136 = 3400 Btu/F of thermal capacitance. With minimal heat loss to the ground underneath, a 50K Btu/h boiler might warm it 100K/3400 = 29 F in two hours.
At this point, 4' of R10 perimeter insulation seems like a good idea, along with baseboard radiators...
Nick
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On Wed, 4 Feb 2004 09:29:30 -0500, "Tom Newton"

Where in NY are you?

Is the tubing PEX? If so, 180 is the max temp allowed and really more than you want to be putting into the floor. Give it a few days before getting too excited. With the temps we've been having it may take 3 or 4 days to bring things up to temp. What we'd expect to see would be the return temp rising slowly. But you may need to get your incoming water temp down. 140 would be a starting point.

Relax for a couple of days and see what happens. Plenty of time to get excited later.

Generally, you put it what's required putting in more than is required won't necessarily hurt anything as long as it's been designed properly. You need to know how many gpm at what temperature drop will heat the area. Then you have to install a pump that will handle that flow at the required head.

Well, it may not be the end of the world. If there is good perimeter insulation at least 24" down. By good I mean R-10 minimum. Would insulation under the slab be better? Absolutely. Are there radiant systems in NY heating homes w/o under slab insulation? Yes. Will you're bills be higher? Yep.

This leads me to believe he's a bit out of his depth here. The perimeter insulation needs to be done. Like I said, R-10 minimum for at least 24" depth. Next you need to know what the heat loss is for the area as well as how many sq ft of radiant panel there is. That will tell us how many btus need to be delivered per sq ft of panel. Next we need to know how many loops are there? How long are the loops and what size is the tubing?
This could be as simple as changing the external piping or pump.

you're a long way from deciding you need to rip up the slab.
--
Above all things, revere yourself.





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Thanks so much guys for sharing your knowledge. I had a long talk with the contractor today... here's an update. By the way, my location is Long Island NY... average evening temp in Feb about 25 or so, the ground below is dry and densly packed earth with some clay
We just had a frank talk...
1. He explained why the insulation didn't go down (the subconcrete below the first two inches was too hard and too dense to get any lower... his guys were jackhammering it for several days... it would have taken TNT to blast it down any further -- based on what I saw at the time, I take him at his word.) So, one inch of insulation on top of the slab as it was would have translated to 2" or more height to the final product... which would admittedly have been undesireable -- but again -- perhaps baseboard heat would have been a better reccomendation at that point... even though I did express distaste for baseboard from the start...;
2. I explained that -- while I did want the end result tile floor to be as flush as possible as the oak in the main part of the house (he's done a goo sjob achieving that.. it's only 1/2" higher) -- I didn't feel that he had educated me to what the ramifications would be by not insulating the slab (ie heatup time, and heating costs)... but again, he says... Tom, we hooked this up 24 hours ago, don't freak out yet, it takes a long time to get this baby up to temp... lets not freak out yet...;
3. We called the heating guy... who helped my contractor (Bill) with the heat calculations, the pressure tests, the hookups to the boiler, and when I asked him if putting radiant heat on an uninsulated slab is OK, he says "optimally no... but does it happen often? yes -- does not having it insulated mean you're doomed? No.;
4. He had put 6MM plastic below the pex tubing , which sits on a rack of sorts and then the whole thing gets flooded with the cement etc... 6MM of plastic seems minor, but the heat guy says that it helps;
5. He has agreed to insulate the exterior perimeter of the foundation (6" above ground, and 18' below) around the slab "at cost" ... but I'm working with him on a number as close to free as possible;
6. I explained that the I hear the water temp should be closer to 130 than 180, and he agrees. There was a mixing valve installed to step the water temp down... but he's had it off so we can heat up the slab.
Anyway, we're continuing to attack the problem --- I haven't told you al labout my 90 year old boiler! Well, it appears that we're at a crossroads with this old war horse too. Hopefully we're able to get an acceptable heating arrangement going shortly.. wish me luck.
Tom
PS. If 130 degree water is going in, and there's 230 ft of pex in the 12x17 area, what's a good target temp for the return water to be? 30 degrees less? 20 degrees less?
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hotmail.com says... ~ Thanks so much guys for sharing your knowledge. I had a long talk with the ~ contractor today... here's an update. By the way, my location is Long Island ~ NY... average evening temp in Feb about 25 or so, the ground below is dry ~ and densly packed earth with some clay ~ ~ We just had a frank talk... ~ Details snipped.
I think your contractor should have consulted you before going ahead without insulating the slab.
The extra insulation at the edge of the slab will make a significant difference in the temperature of the ground under the slab because the "temperature gradient" will be much flatter. That doesn't excuse the builder, but his offer to install the perimeter insulation at his expense seems fair.
See: http://tinyurl.com/2au9y
It will explain why insulating the perimeter helps, and will show you the detail of how it should be done. Ask for the builder's assurance that he will follow this or something a lot like it.
Rick
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snipped-for-privacy@shaw.ca says...
~ hotmail.com says... ~ ~ Thanks so much guys for sharing your knowledge. I had a long talk with the ~ ~ contractor today... here's an update. By the way, my location is Long Island ~ ~ NY... average evening temp in Feb about 25 or so, the ground below is dry ~ ~ and densly packed earth with some clay ~ ~ ~ ~ We just had a frank talk... ~ ~ ~ Details snipped. ~ ~ I think your contractor should have consulted you before going ahead ~ without insulating the slab. ~ ~ The extra insulation at the edge of the slab will make a significant ~ difference in the temperature of the ground under the slab because ~ the "temperature gradient" will be much flatter.
Oops. I misspoke. The temperature gradient won't be flatter. The temperature gradient depends only on the temperature difference and the conductivity of the soil. The insulating value of the soil will be higher because the route from slab to exterior ground surface will be much longer.
Rick
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Thanks Java Man
That URL you give doesn't work... please give me the link - thanks!
Tom

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hotmail.com says... ~ Thanks Java Man ~ ~ That URL you give doesn't work... please give me the link - thanks! ~
http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/2000-127E.html
Rick
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And another thing.
Don't even think about a setback thermostat . Leave it on and leave it at set temperature. Even if you leave for the weekend. Expect it to take 72 hours to stabilize after your 10 day ski trip when you do set it back 10 degrees.
PJ
On Wed, 4 Feb 2004 09:29:30 -0500, "Tom Newton"

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Given the slow response time of radiant heat.... as per your statement above..... is this one reason why YOu might avoid using that "type" of heat?
Are ALL radiant heat systems just slow to respond.... and the nature of the beast?
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On Wed, 04 Feb 2004 14:48:12 -0600, snipped-for-privacy@privacy.net wrote:

I think you are onto something important. It is nearly always about "comfort" when you are talking about these radiant systems.
I prefer efficiency as much as comfort and could never justify the cost of such a system for myself or my fat wife although operating and installation costs are coming down for radiant systems.
Slow? Depends. If it is an upstairs bathroom, then it should come up to temperature in a couple of hours. If it is in a full basement then a couple of weeks might be necessary to get the full effect of radiant heat.
PJ
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snipped-for-privacy@privacy.net says... ~ I prefer efficiency as much as comfort and could never justify the ~ cost of such a system for myself or my fat wife although operating and ~ installation costs are coming down for radiant systems. ~ But what if you had a skinny wife?
Rick
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PJ -
What's a setback thermostat?
Thanks!
Tom
wrote:

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Here is a nice description: http://www.eichlernetwork.com/messages/6869.html
On Wed, 4 Feb 2004 17:10:50 -0500, "Tom Newton"

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Tom Newton wrote:

So, it's been 2 days. Any change? It may take a week (or even more) to warm up that slab and the several feet of earth underneath it. The exterior insulation sounds like a really good idea. If the return water was warm and you still had cold rooms, then you would have a disaster, ie. not enough heat exchanger surface area. I suspect you will be seeing some improvement already.
Jon
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Jon -
Thanks for your concern. Yes, thankfully, it's warmed up nicely --- especially since the air was removed from the system...
At any rate, we're doing two things 1) insulting the outer perimeter or the slab, and 2) getting a new boiler (the old clunker is struggling at 86 years old)...
Still a long way to go... but we're heading in the right direction
Tom

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