slab heating help

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Old 01-05-12, 05:55 AM
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slab heating help

Goodmorning,

I am looking for some help/advice on heating my 1950 slab house.
We just bought the house this past summer and i have some questions, or concerns with my heating system.
The house is 900sqft slab house with a crude radiant heat.
1/2in copper embeded in the slab pusing 180deg water from a york boiler hanging in the kitchen.

The house is a origonal levitt house.

On the warmer days the thermostat will call for heat one time a day and heat the house to 65deg in about 90 minuets.

the house holds the heat well and has alot of solar gain.

Now that the wether had dipped down a bit the thermostat will call for heat more often, but will always take about
90 minuets to be satisfied.

We keep the thermostat at a steady 65deg with no setback.
I feel that the slab is getting too cold during the times that the heat is not being called for
and taking too long to get back to temp.

Does this seem right? any thoughts
 
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Old 01-05-12, 03:46 PM
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1/2in copper embeded in the slab pusing 180deg water
You want the bad news first? OK, here goes...

After 50 years embedded in concrete, copper pipes will begin to develop leaks. This is the fate of those early radiant slab homes, sorry to say.

Have you talked with the neighbors about their systems? (assuming this is tract housing and all the homes in the neighborhood share the same type of heating) How many of them are still using the radiant heat system, and how many have converted to either baseboard heating, or forced hot air?

Running 180 water through the slab we have learned is not a real good idea either. The floor will ultimately get too HOT to put your feet on... but probably only in certain rooms, i.e. the bathroom. Other rooms will probably be cold... especially the 'outer' rooms, but in a 900 sq ft home, you may not have that problem. ( I grew up in an early radiant heated home, an ell shaped ranch, and the Master bedroom with three exposed walls was NEVER warm )

The slabs these homes were built on were never insulated, either under, or around the perimeter. There's tremendous heat loss there. You end up heating the ground. There's one advantage though, if you build a 'cold frame' up next to the foundation, you can grow fresh herbs and some veggies all year long... ( we did! ) and the concrete pad porches will never need shoveling of snow. When it snows, there will be no snow accumulation within 1' of the slab.

york boiler hanging in the kitchen.
This doesn't sound original to the home... why is it in the kitchen? and 'hanging' ? what do you mean? What is the model of the boiler?

Another problem that these systems suffer from is COOL RETURN TEMPS to the boiler for very extended periods of time, and this will eventually destroy the boiler due to 'flue gas condensation'.

Sorry for all the bad news, but you should know objectively what problems you will possibly be faced with in the future.

So what can you do?

Insulate the perimeter of the slab to reduce the heat loss.

Take advantage of the cool return water and install a 'modulating/condensing' boiler which will give higher efficiency BECAUSE of the cool water returning. They are designed for the conditions that exist and gain their extra efficiency due to the condensing feature.

Run an OUTDOOR RESET control which will limit the temperature of the water that runs through the slab and allow for shorter burner cycles, but longer circulating cycles... lower temperature water for a longer time will result in more even heating. CONSTANT circulation would be a huge advantage in evening out the temp swings. By constantly circulating water that is only hot enough to counter the heat lost would be a good thing.

Unfortunately, none of these options are exactly cheap...

except, PRAY that you don't develop leaks in the tubing in the slab!

BTW, did Sal REALLY paint you? which one are you?
 
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Old 01-05-12, 04:24 PM
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Does the temperature indicated on the thermostat drop below 65? If it doesn't go lower than 64, the cold feel of the slab is probably because it's concrete at room temperature. I think you should get a temp gauge setup on your return line to find out your return temps. If it is high enough, you may be able to lower your supply temp for a longer run time. A longer run time will keep warmer water in the slab for longer and feel nicer.
 
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Old 01-05-12, 06:44 PM
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NJ thanks for the advice and warnings, yes these are tract houses. Built on long island in the late 40's and 50's Levittown. I am aware of the down fall of the early systems, but the price was right and the house had a lot of other things that made us buy it. Hoping to get a season out of the heat. I have heard horror stories where people's living rooms have looked like sprinklers. I am pretty sure I have no leaks so far, I put a pressure gauge on the system before the heating season and it held 25 psi for a few days. Also when I have attempted to bleed water out it comes out extremely clean.

The boiler as I am mistaken is a GE model, original to the house. With a Beckett head that was replaced in 1978, the original GE head was a bit of a rube Goldberg I am told. I will take some pix this weekend for laughs.

All of the neighbors I have spoken with have abandoned the radiant due to leaks and gone with baseboard. Which is a project I have planned for after the heating system , 3 zone along with a indirect water heater from a peerless 3 section cast boiler.

I am really just hoping to make it though this heating season,
But I wasnt sure how this really was supposed to go. We are new home owners and our last rental had baseboard.

Drooplug. The slab never seems very cold, but it seems that the thermostat will call for heat, and get satisfied after 90 minutes to 2 hours, and then not need to be called again for another 8 to 12 hours. And by that time the slab is very cold and the return water is very low. Where as if I were to raise the thermostat and make it call for heat an hour after the last call the return temp is much higher because the slab is already warm, causing a quicker time for the thermostat to get satisfied. Does that make sense?
 

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Old 01-05-12, 07:11 PM
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OK, glad you knew what you were looking at and had a plan...

What kind of thermostat is installed? I wonder if there is one that might be more appropriate for the system... something that you can set the 'anticipator' for shorter cycles. Might tend to even out the temp swings.

After you do the heating system over, you would still be wise to insulate the perimeter of the slab as best possible.
 
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Old 01-05-12, 07:22 PM
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I don't think there are temp swings. The OP is complaining about the slab being cold. I think its just because it is concrete.

My in-laws live in a levitt house with the in floor radiant. In floor radiant is slow. The great advantage to your in floor radiant is the concrete. There is a lot of mass there and that's why the heat stays off for so long. It also takes a long time to heat all that concrete up too. Do you ever feel hot spots in the floor while it is running?

I don't know if your system has it, but most modern setups will have an autofill on the boiler to make sure the systems stays at pressure if it loses some water. In your upgrade endeavors, put a water meter on the make up water line. This way you will be able to tell if the system is refilling itself because of a leak. I think furd has mentioned this a lot in his posts.
 
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Old 01-06-12, 05:29 AM
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Maybe i should restate my question. I dont think the slab is getting cold.

Ok here is how i assume my radiant system works.
thermostat calls for heat.
circulator pumps, and when temp drops boiler fires
hot water enters and gets cooled at it warms up the slab.
after an hour or so the slab starts to emit the heat it has gained from the water
the themstat is satisfied and shuts off.

Hours later the slab has lost all of its heat to emit (i said cold but i mean its lost its heat to emit)

so the whole process startes again and takes that 90 minuets to warm the slab again.


Im not concerned that the slab is cold, it never really feels cold. I am wondering if the slab is cooling off too much for the system, meaning that the water and boiler has to bring it back to temp, and because the its at a lower temp the process will take the same time.

I feel like i should have a way to get the slab to temp, and keep it there more consistantly.

make sense?
 
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Old 01-06-12, 07:42 AM
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Ok, so the problem is really that you're seeing temperature swings which are wider than you think they should be; that the system is not cycling often enough?
 
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Old 01-06-12, 08:38 AM
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more or less yes. it seems that th system would run a whole lot more efficient if the thermostat would kick on while the slab was still hot. so that the return water didnt get so ice cold.

the thermostat is a 110v thermostat dial type, not sure of model number, or mae. i will bet pics of that too tonight
 
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Old 01-06-12, 06:04 PM
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Your system is working the way it needs to. It is only putting the amount of heat into the home that is required to maintain the air temperature. You can design a system that will pump water of a lower temperature for longer periods of time. That will definitely provide you with more comfort, but not necessarily with more efficiency.
 
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Old 01-06-12, 06:09 PM
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the thermostat is a 110v thermostat dial type,
Is the thermostat original to the home also? Not many line voltage thermostats around these days. I

I would be that if you replaced that with a low voltage digital, and use a relay to trigger the boiler, you will have more accurate temp sensing... I would bet that the existing t'stat has a wider 'differential' than a modern t'stat...
 
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Old 01-06-12, 06:20 PM
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I don't see any indication that there is an air temperature problem here. The OP is saying that the slab cools off too much before the next heat call and thinks the system is wasting energy operating in this fashion.
 
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Old 01-07-12, 10:38 AM
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Hello...i'm down in Lindenhurst...and those Levitt house styles have just raw copper and concrete poured in tracking those homes.once the winter is done start stocking up on Slant-Fin lenghts,and you won't feel it that much $$ when you do the change out.soldering is easy and we'll walk you thru it.the concrete pour isn't insulated from the actual ground so your heat is tripping into the dirt in the dead of the winter.try to get it this spring don't push your luck .this simple... Slant/Fin Baseboard Installation - YouTube
 
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Old 01-07-12, 06:07 PM
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drooplug.

you hit it right on the head there, is that normal operation?


sminker
thats the plan... cant wait
 
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Old 01-13-12, 08:56 AM
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pictures

here are a link to the pictures of my boiler and the return manifold. it was very hard to get good pix as i said its a wall hanging boiler in my kitchen.
Pictures by dalipaintedme - Photobucket

whatcha think
 
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Old 01-13-12, 09:14 AM
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whatcha think
Hope that white stuff covering everythig isn't asbestos.
Some please tell me it isn't so.


Peter
 
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Old 01-13-12, 09:35 AM
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I suspect that it is asbestos. You can get it encapsulated by an asbestos abatement person.
 
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Old 01-13-12, 05:08 PM
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Get it tested. If it is asbestos, have it removed. Encapsulating it at the point in the game is going to be a waste of money. That boiler isn't going to last much longer.
 
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Old 01-13-12, 05:12 PM
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it was tested when we bought the house with the engineers report. its not asbestos, fiberglass/ portland cement mixture.

More concerned if the system is operating normally?
 
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Old 01-13-12, 05:37 PM
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Yes.

If you are asking if the way your system is operating is normal... which I kinda thought had more or less been answered... then, I would say

"more or less, YES. That is pretty much the way that I would expect your system to operate"

I had mentioned earlier that I thought you would benefit by installing some modern digi thermostats, and I still think you may... Those old line voltage thermostats probably have a wider DIFFERENTIAL than the new ones... even if you can't 'feel' the difference...

What this means with the wider DIFF is that the thermostat will WAIT LONGER before firing the system again. Let's say you are set to 70, and that old t'stat has a 2 DIFF. That means the house will cool to 68 before it fires again... a new thermostat might fire again at 69 ... and that ONE degree could mean that the system fires twice as often... see where I'm going with this?

I'm not guaranteeing it will work... but I'm very familiar with them old slab heated homes... lived in one for over 20 years. I understand exactly what you are trying to achieve. I think that swapping out the thermostats would be a good first step.

That one t'stat looked newer... so I dunno about that one.

I didn't look too much at the pics, just glanced quickly.. I wanna study them up some more... I'll be back.
 
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Old 01-13-12, 05:39 PM
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If those are indeed line voltage thermostats, you can NOT replace them with MOST of the new digitals. You will need a RELAY to operate them.
 
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Old 01-13-12, 06:23 PM
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NJ thanks for the reply.

Im going to set my self up with a relay system so i can go for a newer thermostat, the dial thermostat from johnson controls is what is used for the whole house, and the other thermostat is just for a 12/10 addition that has its own zone.

So im going to give this a crack and see how it goes, i plan on doing a whole baseboard system, and i will probably spend the money on a decent thermostat that i will be using with the new boiler as well
 
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Old 01-13-12, 06:32 PM
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the dial thermostat from johnson controls is what is used for the whole house
Yeah... I dunno... that might not be a bad unit... I was looking at that 'art deco' Honeywell against the cold brick wall...

What's the model number on the Johnson?
(no wisecracks!)
 
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Old 01-14-12, 07:03 AM
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i seems to be a T26S-18C from what i can find under the cover plate, i did some googling and it has a DIFF of 3deg f.

Im wondering if i have a problem though. i was tinkering around last night and it seems that my aquastat is set for 180 deg, and when the water is pumping around the boiler temp drops down to about 140 . my

my return temp from the floor is about 78 deg and my out put temp to the floor is only 98 deg. does this seem right? if the boiler is firing to 180 deg and hitting that limit, why am i only getting 98 going into the floor? my thermostat will call for heat, turn the circulator on, move the water, the water temp will drop in the boiler and fire, the water to the floor is 98 deg, and will move around and come back at 78 deg. the boiler will get cold (140) and fire again and reach the 180 limit. but the temp into the floor will only be about 98-96 deg


this was taken with an infra red gun that i know to be pretty accurate.
 
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Old 01-14-12, 08:07 AM
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It's almost impossible to follow the piping around in the pics, but my guess is that there is a 'BOILER BYPASS' somewhere in the piping... or perhaps even a thermostatic valve somewhere that is limiting the temp to the floor... and if that's true, then this is 'probably' a good thing.

See if you can make any sense of the piping... ID the hot supply from the boiler, follow it out to the manifolds or however it gets into the floor... then the return piping back from the floor... and look for a 'cross connection' between the two.

This graphic that I 'borrowed' and edited (with credits) is a basic idea of how boiler bypass works.



With this arrangement, some of the flow is diverted from the boiler to protect it from too much cool return water entering the boiler, and the temp of the water going to the floor is 'tempered' down by mixing some of the return before it heads back out.

You really do not want 180 water going to the floor!

taken with an infra red gun that i know to be pretty accurate.
In spite of the accuracy, the nature of the material you are measuring can affect the readings. This is known as 'emissivity' (google the term for more info) and is a measurement of the amount that different materials radiate infra-red energy. If you were to measure a piece of copper and a piece of cast iron at the SAME TEMP, the IR gun will give two very different temps.

You can get around this by either painting a spot that you wish to measure with some flat black paint, or even black electrical tape works well. You will be comparing 'apples to apples' then.

Not saying your readings are far off, just point of info about the way those IR guns work...
 
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Old 01-14-12, 08:30 AM
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I wonder if you were looking at the wrong spec... the brochure I found seems to indicate that there is a ONE degree F differential in heating mode.

http://cgproducts.johnsoncontrols.co...df/1922255.pdf

The line below your model shows a 3 in heating mode, but that's C, the number in parens is the F temp.

BUT, I also saw this:

close differential without the need for anticipators
and I think that could be a part of the problem.

Since you've got a HIGH MASS, SLOW RESPONSE system, you NEED an anticipator that is set for SHORTER cycles. Without this, you end up storing more energy than you need in the slab, which then continues to radiate into the home for hours afterward. If you were able to set shorter cycles, and more often, you would have a more consistent slab temperature.

MOST of the modern digital t'stats have a 'self adjusting' anticipator circuit. They measure the 'rate of change' in temperature and adjust the cycle length according to that.

Are you clear on what you need in order to replace the line voltage t'stat with a low voltage digital?
 
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Old 01-14-12, 10:07 AM
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Trooper, I think the anticipator would only make a difference if the thermostat was overshooting the desired temp. I don't recall that being an issue.
 
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Old 01-14-12, 11:43 AM
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Not so... setting the anticipator for SHORTER CYCLES would cause the system to run for LESS TIME, MORE OFTEN, which is what he's looking for.
 
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Old 01-16-12, 05:39 AM
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NJ, i think i have a pretty good understanding on how to do this with a relay. A taco SR501 would be acceptable to do this? also i have a closet right behind the thermostat, would it be acceptable to have the relay right behind the thermostat in order to use the existing 120v wiring to the circulator?

suggestion for a basic thermostat? just a simple honeywell digital thermostat (non programable)
 
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Old 01-16-12, 03:27 PM
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Yeah, the Taco, or Honeywell R8845U, or a number of others as well.

Problem with installing the relay box at (or near) the t'stat is probably going to be that you only will have the 'switched hot' wires available. Since you will need a 120VAC supply to run the relay, you might not have this available at that location.
 
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