# Taco X-pump block radiant heat



## Dan_Watson (Mar 1, 2008)

I have radiant heat, potable system with the Taco X-pump block connected to a water heater and have a few questions. 

What does the 'dem' on the display mean?

What should the target temp be?

How often should the system run?

Everything I have read says it should be extremely efficient, especially in a well insulated house. But, our gas bill has been very high and I am trying to figure out why. I am assuming it has something to do with this system.


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## Golden view (Feb 16, 2012)

Dem means demand.

Target temp depends on what the heat tubes are embedded in.

The common school of thought is that is should run constantly at barely hot enough to heat the house, based on outdoor temp, and the boiler should fire as needed to maintain this temp.

It gets more complicated depending on what type of boiler you have and if there are inefficiencies from short cycling, etc.

There's quite a bit to a well designed system.


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## EricBrancard (Jun 8, 2012)

Golden view said:


> Dem means demand.
> 
> Target temp depends on what the heat tubes are embedded in.
> 
> ...


This would be an open system. It may not actually have a boiler.


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## Golden view (Feb 16, 2012)

Oh, I failed to read the first line. Still not an open system, the X block is a heat exchanger.

What kind of water heater? Most are not efficient.


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## EricBrancard (Jun 8, 2012)

Golden view said:


> Oh, I failed to read the first line. Still not an open system, the X block is a heat exchanger.


True.


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## Dan_Watson (Mar 1, 2008)

Tubes are embedded in the slab. 

Bradford white 75 gallon. Power vented.


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## Dan_Watson (Mar 1, 2008)

The system is not running all the time but just about every time it does the water heater also fires up.


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## Golden view (Feb 16, 2012)

How long does the burner run on average?


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## Dan_Watson (Mar 1, 2008)

I will monitor the next few cycles and let you know.


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## Golden view (Feb 16, 2012)

A few years ago when I did these I would try to get my systems to fire as few times a day as possible. Steady state efficiency is usually highest, sometimes significantly so - the pre and post purge of the power vents can just be spewing BTUs outside.. I got some to run twice a day. The enormous thermal mass of a slab based system helps a lot.

Small zones make this more difficult.

Lots of variables though. You may need to find a local who's really well versed in these systems to have a look.


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## Dan_Watson (Mar 1, 2008)

So it has only been about 12 hrs but the pump has only run once that I have seen but the water heater is kicking on every two hrs for 8 mins.


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## TimNJ (Sep 7, 2005)

I ended up piping in supply and return thermometers on mine.
Goes a long way for trouble shooting as it lets you monitor what your supply is, and then what the return comes back as.
I have mine run at 20deg deltaT and that seems to be a sweet spot.

I use a BoilerMate for my one smaller zone and with the digital thermometer built into it I can set it right to the degree I want. Then a mixing T right off the boiler for my larger zone.


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