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In floor heating - cold floor.


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This house is heated by a hot water boiler that circulates the water through pipes in the slab foundation. After running the boiler for around 30 minutes I could see the loops in the floor with my IR camera. Except in the living room, there was no heat at all. Looking at the manifold one of the loops is clearly cold. Every room had heat, except the living room.

My questions is: Looking at the manifold, is there a way that the zone could have been closed? If so how? Do you use a screwdriver or is there a handel that is attached...

I'm just trying to figure out why only the living room was cold.

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The shut off is a slot blade screw head inside of the hex locknut. If the slot is parallel with flow, it's open...perpendicular, it's closed (at least, that's how they are here).

It could also be the entire loop is shut down due to corrosion and pipe failure. Those copper radiant systems last anywhere from (about) 35 years to 65 years (some maybe longer), but they will fail.

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These were the only valves and I was not about to turn any of them - no way.

Thanks Kurt that was helpful.

At this point I'm just going to report what did, what I discovered and tell them I don't know why there is no floor heat in that room. I'll punt to a company that has experience serviceing and maintaining these system.

Most days I don't find anything with my IR, but sometimes it earns its keep.

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copper embedded into concrete directly = corrosion=leakage=air-entrainment=air-bound.. (Maybe).. (Air entrains during cold period... builds-up.. no movement).

A 'pressure test' of that zone can be done to isolate the problem.. and then give them the heads of the downside of copper-in-direct-contact-with-concrete (=potential leakage, air-binding and over-working of the boiler). We have thousands of these systems from the 1950's around Boston area and they are mostly being upgraded to above-slab systems by now..

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I saw my first boiler (SoCal area) with in-floor PEX under stone, tile and brick. The air temp was already 74 degrees. Set all 6 zone thermostats to 86, computer came to life, boiler fired, stone floors raised 1-2 degrees over a 2 hour period. Is this sufficient differential to call this system operational? As I understand it, high '70s is pretty much all you get from these systems. I'm considering recommending the system be tested again when it gets cold, December or January. Opinions please.

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The idea behind radiant heating is not warm air temps; it's warm everything temps.

The physiology of comfort is about the temperature of stuff you're touching. The floor warms up the walls warms up the furniture warms up toes and everything you touch is warm, about 78?F. So, you're warm.

That's why I think this system is probably just fine. I say probably because without being there and seeing everything for myself, I'm hedging.

Air temps should be about 65-ish, the optimum temp for brain activity.

Radiant is the best of all worlds. Too bad it's so damn expensive.

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Thanks, Kurt and Rob.

I have electric radiant in my living room to help even out a 2 1/2 story house. Turns out we mostly only use it all winter, and we like it a lot. Cost about 3K to install under hardwood. The floor gets to 78 or 80 in about an hour.

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Two degrees in 2 hours is normal here for hydronic on a concrete slab.

I do the same thing you did, watch for a response to the thermostat, then check for a working circulation pump and a gradual rise in temp.

A house with 4 or 5 zones, there's not enough time in the day to check the system thoroughly, which is what I tell the clients. "It makes heat, but I can't tell you how much for how long".

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  • 2 weeks later...

So I asked the realtor what happened with this. She said they had an HVAC company come out and they said everything was working normally. I suspect the HVAC company did not see my report or pictures. I suspect they came out and fired up the boiler, checked the pump, etc and said it is working fine. I suspect they were not told what the specific problem was.

Kinda gets my hackles all worked up.

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. . . Except in the living room, there was no heat at all. . .

I have nothing to add to the technical discussion, but I'm not sure that the sentence above says what you meant it to say.

You are correct. I wrote the opposite of what I intended. Modifications have been posted.

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