Temperature difference before heat exchanger and after

strell

We had to replace our boiler and chose to use a combi that provides both heating and hot water. The combi-boiler has its own internal heat exchanger and pump. The installer (plumber) connected it to the old system such that there is a small circuit from the boiler to 30 plate heat exchanger, then the old pump moves water through the floor heating. The water from the boiler is 68C, from the heat exchanger to the floor is 34C, and the house is 19C. The system can run for hours and we never reach 20C in colder weather (-2C).

What temperature difference should we expect to see before and after the heat exchanger?

Should we replace the old heat exchanger or just connect the combi-boiler directly to the floor heating?

Would it create any problems to connect the combi-boiler directly to the floor circuit instead of being on a separate system? (Would a return temperature of 19C cause a problem? Do I need that bigger pump for a 2 story house?)

The boiler is also pushing water through a second disconnected pump in the old system after the heat exchanger. Is that an issue?

hot_rod

is the radiant tubing a non oxygen barrier type? Maybe that is why there is a heat exchanger?

But the hx should supply the radiant within 10 degrees of the boiler supply temperature, properly installed

An unpowered pump doesn’t sound correct?

mattmia2

What temp is the outlet of the hot(boiler) side of the hx? Somewhere in the boiler menus you can usually find the firing rate of the boiler. There may be little flow through the hot side of the hx or it may be mostly full of air depending on how it is oriented.

EdTheHeaterMan

We had to replace our boiler and chose to use a combi that provides both heating and hot water. The combi-boiler has its own internal heat exchanger and pump. The installer (plumber) connected it to the old system such that there is a small circuit from the boiler to 30 plate heat exchanger, then the old pump moves water through the floor heating. The water from the boiler is 155°F, from the heat exchanger to the floor is 93°F, and the house is 66°. The system can run for hours and we never reach 68°F in colder weather (28°F).

What temperature difference should we expect to see before and after the heat exchanger?

Should we replace the old heat exchanger or just connect the combi-boiler directly to the floor heating?

Would it create any problems to connect the combi-boiler directly to the floor circuit instead of being on a separate system? (Would a return temperature of 19C cause a problem? Do I need that bigger pump for a 2 story house?)

The boiler is also pushing water through a second disconnected pump in the old system after the heat exchanger. Is that an issue?

"The Boiler (Pump) is also pushing water through a second disconnected pump in the old system after the heat exchanger.  Is that an issue?"

I think so.  The Heat Exchanger(HX) separates the boiler water from the water on the other side.  The boiler pump can’t affect the water on the other side of the HX because that water is a completely different system.   Think of it like a pipe that is twisted with a second pipe.  The blue pipe has no water in it that the red pump can move.  Your blue pump is the only thing that can

move the water in the blue pipe. I think you need to power up that other pump to get the heat to move out of the heat exchanger into the floor or what ever you are using for a heat emitter.

"Would it create any problems to connect the combi-boiler directly to the floor circuit instead of being on a separate system?" 

It may if the floor heat tubing does not have a oxygen barrier. Here is why:

https://forum.heatinghelp.com/discussion/200362/the-result-of-using-non-barrier-pex