Controlling an existing hydronic boiler

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Controlling an existing hydronic boiler

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KramerDIY

This is a great article. But I have questions about my own system. I have a very simple closed on-demand system. It uses an American propane boiler to heat 3 zones (total square feet is ~950). I followed the installation instructions that came with my system. But one item that always confused me was the bypass loop they had me include. I had closed the valve on that loop (to force all of the heated water to go through the zones). I just checked and noticed that my input temp was 82 degrees. My output temp is 125 degrees (which is the recommended temp for the unit). So I opened that bypass valve, which of course raised the input temperature to over 100 degrees. This seems to resolve the issue of potential thermal shock. But now I'm wondering how I can change my settings to make my system the most efficient it can be while still providing the heat I need in the house. Is this where I should ask for that advice? TIA.

mikeg2015

You need to check the boiler manual or contact the mfg for the maximum delta T and minimum flow rate across the heat exchanger. Most high efficiency condensing fire tube boilers are 50f at the minimum flow rate. Cast iron boilers might only be 25-30f at most. Some medium mass boilers like HTP will allow 70f or greater. This encourages “stacking” or running loads in series where possible to create the lowest return water temp.

The most efficient setup uses a mix of high grade heat and low grade heat. Radiators use 160-180f, fan coils can use 130-160f, and radiant floor heat is around 90-120f.

So a good setup might be to use a small coil in an air handler together with high temp zones.

Alan (California Radiant) Forbes

That bypass loop is n

KramerDIY said:

This is a great article. But I have questions about my own system. I have a very simple closed on-demand system. It uses an American propane boiler to heat 3 zones (total square feet is ~950). I followed the installation instructions that came with my system. But one item that always confused me was the bypass loop they had me include. I had closed the valve on that loop (to force all of the heated water to go through the zones). I just checked and noticed that my input temp was 82 degrees. My output temp is 125 degrees (which is the recommended temp for the unit). So I opened that bypass valve, which of course raised the input temperature to over 100 degrees. This seems to resolve the issue of potential thermal shock. But now I'm wondering how I can change my settings to make my system the most efficient it can be while still providing the heat I need in the house. Is this where I should ask for that advice? TIA.

I have a few questions:
What kind of heating system do you have? Radiators, radiant (new or old)?
Make and model of your boiler?