Bypass loop for HW Gas Boiler

Neil_5

I have a series 2 150K BTU Burnham HW boiler and everywhere I read that the return line should be above 140 deg to avoid condensation? or something along that line? Can someone explain a bit more to me please?

I don't have this loop, and of course at night with the Stat set back, first fire in the early AM will pump cold water to the return, is this good? I have been to a few new built houses and see no bypass loops as well. Should all cast iron boilers have this loop from the MFG?

Thanks for the insights,
Neil

hr

Depends somewhat

on the type of emitters you have. Copper baseboard is considered a low mass and will usually get up to temperature quickly. As such it is not common to see a bypass or return protection on these systems.

Large cast iron radiators can present a challange do to the mass and larger water volume. With this system it is possible that the return temperatures to the boiler fall below the dewpoint temperature for extended periods.

Certainly radiant systems, specfically those installed in concrete slabs, pose this challange also.

Over the years boiler manufactures have acknowledged this challange. Weil McLain introduced the GV Gold, Burnham the Revolution to address this potential problem. Both these boilers incorporate mixing protection with in the boiler jacketing. This assures the boiler is protected from cold return temperatures.

After market control companies have also reconized this issue. tekmar, and others have had return protection ability built into their controls for years, addressing the radiant market primarly.

Also boilers have shrunk in size and mass over the years. As such they are more sensitive to these cold return temperatures.

Protection can be as simple a a cross over pipe. Sometimes on larger systems a pump is used in this cross over.

Several manufactures offer an aquastat set at 140 that will not allow circulation through the boiler until the block is warmed.

By far the best protection is a control that senses the actual temperature at the return connection and reacts accordingly. This could be a 3 way thermostatic valve, a mixing valve with motor operator, or a VS injection pump.

Primary secondary piping can be used, but it alone WILL NOT not assure return protection without sensing that return temperature.

Soooo a lot depends on YOUR system, the size, or oversize of the boiler, type of emitters and other variables.

Simply grab a bucket saddle up next to the boiler for a couple cold start heat calls and observe the return temperatures. A point and shoot IR temperature gauge, oven thermometer, or a stick on temperature indicator will show you what is happening in your system.

You may, or may not, have a reason to add a protection system to your boiler. Each system is different in it's needs.

Plenty of reading material at tekmars site, the B&G website, and a handful of manufactures articles in recent trade magazines.

Personally I feel the boiler should get up to adequate return temperature within the first 10 minutes. Really is no hard number for this period of time however.

Hope this helps

hot rod

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Neil_5

Very Informative

Thanks for that ...

I have 10 convectors and 3 baseboards, and connected to the system a Tekmar 256. The boiler sitting overnight goes down to about 90-100, so when it first fire up, the temp between the convectors and the boiler is small. I have a calibrated digital thermometer from work I will set up and see what the return line is and how long it takes to reach 140 min.

To explain a bit futher, the low return temp is bad for the cast iron? the liner?

Thanks,
Neil

hr

Yes and yes

the condensate formed from the low temperatures will attack the flue, be it galv, aluminum or clay. in some cases it can rain down and plug the HX and even the burner tubes. This can lead to flame roll out, incomplete combustion (CO)and other issues within the HX.

The wet, acidic conditions will attack even cast iron sections after awhile.

Sometimes these symptoms go un noticed in the far reaches of the vent piping. This is why both hot and adequate duration are important to dry out all the components from boiler HX to final flue runs.

Or you could get a condensing boiler

That tekmar control should have a protection feature?

hot rod

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