New Circuit with circ pump

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Old 12-16-10, 06:12 PM
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New Circuit with circ pump

I have installed radiant heating below my kitchen floor and am getting ready to pipe it into my furnace. I have a new circulating pump to accomidate the friction loss associated with 100 ft of 1/2 PEX tubing (TACO 007 draws 0.76amps), but now I'm concerned that my honeywell Aquistat Relay (L8148E) won't control two circulating pumps. My existing heat runs off a Grundfus UP 15-42 F (draws 0.74 amps) .
The Honeywell manual only shows it powering one circ pump, but the full load is 7.4amps and I'm below this. http://customer.honeywell.com/techli...0s/60-2278.pdf
Do I need a new relay?
Thank you for any feedback
 
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Old 12-17-10, 07:04 PM
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Ummmm... you need more than that I think.

First, how did you install the radiant pex under the floor? there are several methods, and MOST of them require that you run water that is no more than say 120F or so... usually less... in order to achieve this in a system that also uses high temperature emitters, you need to do some special piping and install a MIXING VALVE.

Did you use the proper OXYGEN BARRIER PEX tubing ? the pex tubing used for potable water system is NOT suitable for heating system use.

Once we have a few more details, we can probably help you out, but we need to know what you are working with first.
 
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Old 12-17-10, 08:49 PM
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NJ Troop - Thanks
Yes used O2 Barrier PEX - rated for up to 200 degrees . My furnace runs between 120-140 degrees. Installed with staple up heat transfer plates (two runs per bay) in three 10-ft long rafter bays.
My issue is will I need a new Aquastat relay. I think it will supply enough juice to power two low amp circulating pumps, but I could not find any evidence of multiple pump control in the Honeywell operating manual.

I don't want to fry the relay for the weekend and be without heat.
 
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Old 12-17-10, 09:29 PM
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It's not so much the heat rating of the tubing, but the fact that you don't want the floors that hot! That's the real reason for the mixing valve. If the floors are too hot it quickly becomes uncomfortable. I know this because I grew up in one of the early radiant heated homes where the water temp was uncontrolled...

From what I can gather, your home has only one zone, and you want the radiant zone to run whenever the thermostat calls for heat, right?

I'm pretty sure you won't fry the aquastat, but don't take my word for it... I'd hate to be the one that said, "Yeah, go ahead" and then be wrong, and you freeze yer buns...

If you wanted to play it safe, pick up a relay box like the R8845U which has two relays each rated at 7.4 Amps. Jumper the T T terminals, wire L1 and L2 to C1 and C2, jumper L1 to COM and A, power the circs from NO and B ...
 
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Old 12-18-10, 07:32 AM
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Thanks, and I appreciate your candor on the electrical issue.
I had not considered the "too hot" issue. I am sceptical that it will heat the sub floor, floor and sheet vinyl floor covering to a temperatur that is uncomfortable. If it does, I can remove the insulation below the piping to disperse the heat.

LIfe is an adventure, so we'll; see how it worksout in a few hours.
 
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Old 12-18-10, 08:56 AM
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You might be surprised at how cool 'too hot' actually is. I think the maximum floor surface temperature that you would be looking for is about 85F believe it or not.

The other potential issue is one of possible damage to the flooring materials. Some sheet goods and the glue used to adhere them aren't real happy about being that warm.

Rather than strip away the insulation, which may only serve to waste the heat in a downward direction (you've still got the plates and tubing in contact with the floor), you would do better to do some re-piping and add a 'tempering valve' ...
 
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Old 12-18-10, 08:58 AM
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But then, you DID say "runs between 120-140 degrees." so you may be OK... but that begs the question:

How is it that your system runs at that low a temperature?

What is the make/model of the boiler?
 
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