how to get hot water heat up to attic?

My last hot water question for a while, I promise...
In the new house we just bought, there is a partially finished attic with a radiator. The attic is essentially at 3rd floor level, so the radiator may be 25-30 ft above the basement boiler and circ pumps. I bled the radiator, and air came out of it very slowly---it probably took 30 min for it to fill up. Not surprisingly, in normal operation, no heat gets up there at all.
Is putting in a more powerful main circulator pump a possible solution? If I look at the curves on the Bell & Gossett's web page, some pumps move lots of water at zero head, but others can move more water at a given large head. The pump we have now is rated to go to zero gpm at 24 ft head, which fits with what I described above.
So if I get another pump that fits in the same space, and has some finite gpm at say 30ft head, will this work better? Or am I being naive and the water will merely take the path of least resistance through the lower radiators, and after a while the pipes will burst due to the higher pressure?
Is there another method to divert water up to the attic?
Many thanks,
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snipped-for-privacy@lipid.phys.northwestern.edu (Chuckles) wrote in

Actually, my mistake, I read the wrong chart. The pump in this zone now is a B&G Series 100, which goes to zero gpm at only 8 ft head. It does go up to the 2nd floor, which is more than 8 ft., and maybe that is because of the water main pressure in addition to the pump-created pressure?
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Did you actually bleed the radiator until water came out? Did you add sufficient water to the system so that you actually could bleed the highest radiator in the system?
The other thing to check is to make sure that your expansion tank is not saturated with water. My experience is that in a multi-story house, unless you have a diaphram type expansion tank, over a long period of time, the air tends to migrate from the expansion tank to the highest radiator in the system.
The pump head capacity is not an issue. The pump does not actually need enough strength to push the water to the 3rd floor, as the system should already be full. It only needs to circulate the water.
If you are not getting heat, your radiator valve may be closed, or there might be air trapped in a line between the boiler and the 3rd floor. It is also possible that the 3rd floor radiator is so far from the boiler, that by the time the heat gets that far, the thermostat has already shut down the boiler.
Another possibility, is that in older systems that have been added on and/or converted from gravity systems, where the radiators are connected in parrallel, rather than in series, the hot water will create its own convection, and some of the more remote radiators will not get any heat. In these situations, you may need to add additional circulating pumps, restrictor valves, or otherwise replumb the system so that you get proper circulation.
The key 1st question is whether the 3rd floor radiator ever worked properly. Then you need to figure out exactly where all the pipes go and try to understand what is happening.
Mike Schumann

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[original post is likely clipped to save bandwidth] On 30 Sep 2003 16:13:23 -0700, snipped-for-privacy@lipid.phys.northwestern.edu (Chuckles) wrote:

Don't confuse pumps with circulators. Once the system is bled of all air, the down pressure on the return just about equals the pressure needed to pump water up. There is no concept of head that applies.
That's why they are called circulators, not pumps.
A few possibilities:
- the system isn't totally bled
- ther is a path of lower resistance, fluids always (almost) pick the path of lowest resistance.
gerry
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On 30 Sep 2003 16:13:23 -0700, snipped-for-privacy@lipid.phys.northwestern.edu (Chuckles) wrote:

Measure, don't guess, the height of your system in feet. Divide by two. This is the minimum pressure (psig) you need on your boiler. The pressure regulating valve must be adjusted to maintain this minimum pressure, even when the boiler is cold.
You're welcome. :)
Gary
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Why? What will happen if the pressure is lower?
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