Gravity Conversion

Alan(CaliforniaRadiant)Forbes

That was a great topic we had on pump sizing for gravity conversions. Everyone had something to say about it and to tell you the truth, the math got to me after a little while. I hated most of my math teachers and they hated me back; I didn't learn much.

Sold my first Vitodens; model 8-24. I'm doing all the wrong things; ballpark sizing, condensing boiler on a radiator system. Besides being bad at math, I'm extremely lazy and never learn from my mistakes. But the guy's boiler flooded and I felt as though if I didn't jump on it, he'd call someone else 'cause he wants the boiler installed next week.

So I don't want to blow it entirely, OK? I want the system to work well, heat evenly on continuous circulation, but am wodering about installing a low loss header which is there to de-couple a high flow rate system from the boiler. As we all know, a gravity system is not a high flow system. So, can I make do without the low loss header?

What say ye?

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Online Sheriff \"Murph\"

here ya go.....

break the system at the first split then reduce the size by half plus one IE: 2" pipe to 1" to 3/4" to get back pressure on pump to circulate!! got it, great !!



Murph' (SOS)

Alan(CaliforniaRadiant)Forbes

I'm OK

with the pipe sizing; just want to know what to do with the near-boiler piping:

1) Use the low-loss header

2) Primary-Secondary, or

3) Use the built-in pump straight to the system


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Paul Pollets

Use the low loss header

or you'll have bigger problems. The Vitodens is meant for condensing loads, ie radiant floors. It will work with radiators, but it would be nice to add a RFH zone. You'll see a drop in efficiency, from 95-96% to perhaps 86-91%
A cast iron boiler (staged, if possible) works better with cast iron rads. I'd be careful to balance the system with TRV's at the radiators, if budget allows.

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Alan(CaliforniaRadiant)Forbes

TRV's

will make the system work much better than it ever has; I agree.

One of the reasons I'm going with a Vitodens is the wall-mounted feature. The previous boiler (A. O. Smith Burkay for heavens sake) was on the floor and submerged under water when the sump failed. The new boiler will be less likely to see water if it's up high on the wall.

Murph' and Paul: thanks for your help.

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Mike T., Swampeast MO

Hey Alan,

From what you say and profess to do, you produce radiant systems working under reset/constant circulation so nicely that occupants find little need for the thermostat...

And you say you don't understand math? Ha! You have your tube laying to an ART! The two are so closely related that it's difficult to determine which is which sometimes, but it's hard to comprehend either without both.

As long as your systems are reasonably straight-forward, who cares if Tek-Mar did the "hard math" for you?

Mike T., Swampeast MO

The gravity conversion

USE TRVs!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you got anything from the discussion about flow in gravity systems, you found that they work PRIMALLY different under "forced" and "natural" flow.

While the mass of the converted gravity system can mask LOTS of "sins" when operated under digital control, YOU "see" proportionally. By designing (AND BALANCING) radiant systems to the point where the thermostat amounts to little more than an object on the wall you see WAY beyond the norm.

DON'T bog yourself down in the math--it's nearly beyond comprehension when applied in the real world anyway.

Let the TRVs do the "hard math" for you JUST LIKE Tek-Mar!!!!!!

Alan(CaliforniaRadiant)Forbes

OK - No problem

TRV's are the way to go. There are only 6 cast iron radiators in the house. Someone else installed some funky BB in the living room and entry and I'll leave these alone (without TRV's) since they're undersized and they can be a bypass when the TRV's are closed.

Here a shot of one of the bedroom radiators; 1-1/2" feed.

The second shot is of the flooded boiler in the concrete vault.

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