Viessmann return water temperature

DC123

Is there any way to figure out the return water temperature on a Viessmann boiler (CU3A)? It only gives me the system temp and the flue gas temp - is this actually the more important number in terms of determining where you are on the efficiency curve? The manual says flue gas temp can vary from 9-27F over the return water temp, but I'd like to figure out what my delta T is a little more effectively.

Solid_Fuel_Man

Are you looking for something strictly for setting up pump speed and calculations, or a perminant temp readout. I'm not familiar with the CU3a control. But it is a sweet boiler!

EBEBRATT-Ed

If you wan't to know your delta T, measure it with a thermometer

DC123

Yes, re pump speed. May end up getting a couple temp probes, but figured the boiler should have it already measured. But if flue temp is as good or better to work with, I can just use that instead. Seems odd that viessmann wouldn't report such a basic parameter.

Solid_Fuel_Man

I really like these

https://www.supplyhouse.com/Azel-Technologies-DS-60P-Dual-Zone-Digital-Temperature-Gauge-with-Two-Universal-Sensor-Probes

Used many of them, have internal battery which lasts about 1.5 years and/or you can feed 24 volts a.c. to them from boiler controls.

NY_Rob

^ I use the same Azel units on my boiler....

DC123

Thanks, that looks like a reasonable one. Any sense of whether flue gas temp is a better parameter than return water temp to evaluate?

NY_Rob

The mod-con efficiency charts (that I've seen) are all based on return water temp, so to me that's what counts.

Alan (California Radiant) Forbes

Solid Fuel Man:
Excellent call on the dual sensors! I gave you an "Awesome" vote.

Solid_Fuel_Man

This is my own control panel as in my avatar. I have radiant supply and return, as well as indirect tank temp and boiler return temp. I just wish there were not 50 bucks a piece! But very good quality none the less.

Canucker

Very clean set up @Solid_Fuel_Man I like it