Venturi System Combined with Conventional System

[masstech]

I recently did an oil to gas conversion boiler changeout. The existing piping is as follows. Boiler is heating first floor only (1200 ft/2). 2 zones because addition had been done a few years back. Why they didn't tie into existing system I'll never know. The original zone is a venturi type system, 1 1/4" main with branches coming of at each baseboard. The 2nd. newer zone is conventional 3/4" supply in one end of baseboard out the other back to the return. The homeowner just wanted the boiler changed, no piping work. After installation I bled all radiators upstairs on the old system and purged the other zone in the basement with P&B valves. The original venturi zone doesn't seem to heat up like it should. Now keep in mind that I didn't know how the system operated before the changeout so I have nothing to compare to. For all I know it was never a balanced system. Should there be venturi tees at each baseboard supply and return side? There doesn't seem to be any on the system but I could be wrong. Some of the baseboard piping is in a crawlspace and haven't had a chance to verify. I've heard that venturi tees should be on supply side only and some people say on supply and return.

[beenthere]

Supply and return if the heat emitters are below the piping.

But if your using circs for zoning. The baseboard should have no efect on the mono zone.

Did you change out the old circs.
If so, you probably have the wrong circ for a mono system.

[masstech]

I did replace the circulators with new Grundfoss circs. with built-in flow check

[beenthere]

Are they the 3 speed Grundfoss, or single speed.

[masstech]

One is a single speed which came with the boiler and the other is the 3 speed. I'm not sure which one is on the mono system. I have the speed set to "2" on the variable speed circ.