DoTaco 007's fail gradually over time?

Hugh Mason

We have a simple single zone radiant heating system that we've successfully heated with for four years. A little Dunkirk XEB-2 boiler provides heat to a 40 gallon range tank regulated by a thermostat (on at 120 off at 145 to minimize short cycling) and then a Taco 007 pumps water tempered via a Watts three way tempering valve to the slab. I monitor the boiler return temp. (keeping it above 140) and the slab in and out temps.
If memory serves me correctly, the slab in and out delt-T was about 6 degrees initially. Today I'm seeing nearly a 30 degree delta T.

The Taco floor circulator is running constantly but the high delta T makes me feel that its lost much of its pumping capacity. I should add that this has seemed to degrade gradually over the last 4 years not just all at once.

One other factor- The slab tubing's oxygen permeabilty is suspect so corrosion is a distinct possibility.

What do you think?

Hugh

bill clinton_3

delta t

You could be onto something: If that's a cast iron 007 and there's no oxygen barrier, it could be building flow blocking corrosion inside as could other components.

On the other hand, I'd think hard about that memory of 6 degree delta tee. With an 007 pushing the water and the tube embedded in a slab, a 6 degree delta tee would be a very pleasant but large surprise. Would have to have short loops and small heated area for that to occur. Twenty degree delta tee for a fully warmed up system is in the range of normal. Thirty degrees (once slab is warmed) would probably indicate need for shorter loops/ bigger pump, but plenty of systems get along even with that.

So, either you're right that performance has degraded as a result of corrosion (pull pump apart to see), or this is just the way the system is. If you decide you need more performance, use a bigger circulator.

Bill

Hugh Mason

Bill,

The system consists of one 200 foot loop of 3/4 pex in the middle of a 4" slab. There is 2 1/2 inches of Dow Blueboard insulation under the whole slab which is ~ 3 feet below grade. (Super low heat load dome house) The head must be very low with the short loop, large bore tube and lack of many other fittings, elbows etc.

Thanks for the feedback. I'll pull the circulator apart when our outside temperatures moderate a bit.

Hugh

John Ruhnke1

System may be slowly pluging up

Hugh,

I just did a job for a client that had non oxygen barrier tubing. The loops were all blocked or partly blocked from debree with metel shavings in it. We blew it out with a mixture of 150 psi air and water. Works fine now. Also we installed a heat exchanger inbetween the boiler and the radiant tubing to isolate the nonbarrier tubing from the boiler. The steel in the boiler consums the oxygen and forms rust.

JR

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Hugh Mason

John,

Thanks so much for the feedback. It looks quiet likly that the best long term fix would be a nonferrous pump plus heat exchanger to isolate this loop from the range tank and boiler. I'd hate to hole the boiler due to oxygen issues.

Hugh