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Boiler Replacement Question

Brad White_9
Brad White_9 Member Posts: 2,440
re-think a few of your parameters, Mike-

But first, let's get to your easier question, protecting the boiler. Primary-Secondary is one way, the primary loop is the bypass essentially, circulating boiler-temperature water, splitting off for injection some of that and taking back an equal amount to the boiler. The boiler sees a reduced temperature but not below the limit if set up correctly. 4-Way mixing valves are another way to accomplish this... It will also establish your secondary temperature to your radiant floors.

Now, some of your parameters and assumptions:

I would re-think the one-zone concept. The sun shines on at least two sides at any given time and the sucker moves all day. So will your heat gains. With a good manifold you can have each room get it's own balancing if not control.

Water temperature: Go to the "SHOP" tab above and get a RadPad is one short suggestion. The RPA also has books as does Dan on this site. A little study will do wonders- SO MANY variables... Heat loss, floor construction, location of tubing at what depth, spacing of tubing, floor covering.... need I go on... Point is, each room is likely to have a different density of tubing because of it's heat loss and the amount of available radiant floor...

I would do this soon.


  • Mike Curran
    Mike Curran Member Posts: 3
    Boiler Replacement

    I am a HVAC Contractor in St. Louis, Mo. We do very little hot water or steam heating in this part of the country. Having said this, we are replacing a 30 year old cast iron boiler with a new cast iron boiler for a customer. It is a simple system, radiant floor, entire house is one zone, no outdoor reset. I want to make sure I protect the boiler from low return water temp. Will a primary/secondary pumping set up provide enough protection? Or do I need to install a bypass line. Also, it is my understanding that the desired floor temperature for this type of system is 85 degrees. What should the water temp be set to? Any advice would be greatly appreciated!
    Thanks in advance from a wannabe "wethead"
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