Can radiator supply pipe have a dip in it?

tom_130

I am adding a radiator to my two pipe hot water system. The system must have been a converted gravity system as the main supply and return pipes are 3 inch diameter and most of the radiators are 1 1/4" pipes. I am tapping into two old fittings that were capped long ago when a radiator was removed from the kitchen. I am trying to come off the old fittings and make a 25 foot (50 foot round trip) run to the new radiator using either 1" or 3/4" copper pipe. There is a steel beam in the way of my horizontal path so in order to get across this beam I must drop the pipe down 2 inches and then it will need to go back up those two inches and off to the radiator. Can I have this low spot or dip in the run or
will this cause an air bubble blockage in the pipe? Can I or should I put a bleeder valve on the line? I can't go over the beam. Any ideas? Also is it OK to go to 3/4 inch pipe when all the other radiators are run at 1 to 1 1/4 inch? The 3/4 inch pipe will make my run to the radiator easier because the pipe needs to go up between a joist and a brick wall. I can run as much as possible at 1 inch and then reduce to 3/4" if it will help.
Other facts :new radiator is rated around 14,000 btu,
my boiler uses a Bell and Gossett series 100 pump, and has an output of 144,000 btu, we have a total of 8 radiators in the house 7 in the 12,000 to 15,000 btu range, and 1 around 5000 btu.
Wow that is lot...
SO the questions were...
1)Can I have a low spot or dip?
2)Is the 3/4 inch pipe sufficient?
3)Would using 1 inch pipe for most of the 25 ft run help any?
Thanks a bunch,
Tom
PS Should I connect copper fittings directly to the iron pipe?

Big Ed_4

Rad

First off copper adpter is ok. With the air trap a bleeder can be used on top of all air traps. But I would use a purge valve set up on one riser end. Dropping down to 3/4 will restrict the flow down compaired to the other radiators running under one inch. The lenght and all the fitting add to the restriction. Now if this is a wing or addition it should be zoned anyway.

tom_130

Can one radiator be a zone?

Thanks for the input.
If I zone the small addition, I will be having only one 15,000 btu radiator on that zone. Is that a problem? I was looking at a TACO zoned system, but I am just figuring out how the zoning is accomplished. Any simple cost effective systems you would recommend?
Thanks
Tom

Big Ed_4

Zoning

Not a problem zoning one radiator. Your addition with more exposed sides will have a greater heat loss then the rooms in the main house so it should be zoned. Any floor or wing should be zoned.

That one radiator. You can now run a 1/2" line if you like , you also need a small circulator , thermostat , relay and flow valve. You can buy a circ with a built in check for ease of install. They also make a circ with a built in relay.