Water running backwards through boiler

gardenweasel

First, thanks to everyone here - I've done a lot of lurking and you've all helped me a lot already.

The players:
1993 Columbia MCB100 boiler
Old converted gravity system with iron pipes and iron radiators
3-story semi-attached Philadelphia rowhouse

I recently redid the copper piping between my boiler and the iron pipes from the old gravity system. A ball valve had started to leak and was dripping water into the boiler jacket. That all went pretty well but it wasn't until I finished that I realized the way things are currently piped (and have been since 1993), the water is running backwards through the boiler - meaning the return water is going into the pipe on the top and the heated water is going out the side of the boiler and through the circulator.

It wouldn't be hard at all to isolate the boiler and flip the Taco so it runs the other way, but then I have water running the "wrong way" through the radiators.

I guess my question is, barring a redo of all the piping I just did (not happening) is it preferable to have the water running the wrong way through the boiler like it's currently set up or to have the water run the wrong way through the radiators? It's presumably been running this way since 1993 and it seems to be no big thing. The only "change" I made to the setup was downsizing from 1-1/2" copper to 1" since it was cheaper and easier to work with and the flow requirements didn't need anything bigger.

I expect to need a new boiler in a few years but I wanted to extract a few more usable years out of what I've got by killing the leak and replacing the broken altitude gauge, very rusted iron nipple at the top of the heat exchanger and the safety blowoff valve (it was stuck closed and so it was useless/dangerous.)

Jamie Hall

Counterflow… well, considering that it is being pumped, it will make very little difference. It might even lead to a slight increase in efficiency, oddly enough -- but I doubt that it would be enough to notice.

If it were still gravity, it wouldn't work as well -- although it would probably still work.

JUGHNE

How are your radiators connected.....bottom to bottom?

gardenweasel

Yes - bottom to bottom. As it stands the heated water enters through the valve side and exits on the other.

JUGHNE

I don't think it would matter with the radiators.
The return piping was usually 1 size smaller than supply, however with the pump connections at 1", I doubt if the water flow would be affected considering that all your pipe is oversized.

One thing to consider is the location of the pressure tank and the fill valve. If the pump pulls on the side with the fill valve it will drop the pressure there and add more water via the fill valve.
One system I know of with pumps pushing into boiler, fill valve after pumps and compression tank with air separator on boiler output used to have a problem of overfilling. It has a LWCO and I shut off the water supply, this has made things more stable.

gardenweasel

Thank you - the expansion tank and fill valve are on the supply/heated water side of the pipes. The pump currently pumps toward them. The fill valve isn't automatic though, it's just a ball valve, so it really can't overfill.

flat_twin

Excellent demo of what happens when you pump away or pump toward the expansion tank (also called the point of no pressure change, ponpc)
https://www.youtube.com/watch?time_continue=10&v=tZRuqiQkukE