original circulator sized too small?

either a heat load calculation. Or a total of all the heat emitters connected would determine required flow. Possibly the boiler is oversized ?

121 feet of fin tube would be around 66,500 btu/ hr, figure 550 btu/ ft as an estimate for residential fin tube

What problem are you trying to fix?

Are you sure the 120' section isn't fed from a tee in the middle with a return at both ends or fed from both ends with a return in the middle?

Does the boiler cycle on and off on high limit while the thermostat is still calling for heat?

If you have twice that length of baseboard that is abut 130,000 btu/hr which sounds adequate to oversized for anything but the most extreme climates for 2000 ft^2 unless you have something unusual like a couple walls made entirely of glass or something.

You may not have enough circulator although my bet would be on something else like trapped air or some sort of boiler or piping issue.

That sounds more like either the circulator isn't working at all, there is a bypass that is stuck open or open too far, it is air bound, or some valve is closed somewhere.

Is this all one zone or are there zone valves?

You should do a heat loss calculation to confirm but I would expect the heat loss of a 2,000 ft^2 house in a northern continental US climate to be under 100,000 btu/hr even if it is uninsulated. If it is 2 stories it only loses heat on the outside walls and roof so the first floor has relatively little heat loss per square foot.

What happens if you manually open the zone valves, does more of the piping get hot?

Can you show some pictures of the boiler and piping? In this type of system the circulator is usually run off the end switches on the zone valves.

it is only circulating by gravity if that is happening. figure it out and your gas bill will go way down.

The oo7 is undersized.

1 Give us an idea of the total feet of Fintube with actual fins

2 give us the length of run of the longest circuit

@wyatts Said: "its not a 121 foot loop. off the boiler is a 1 1/4 supply that feeds into two zone valves. off each zone valve is a 1 inch supply these feed the upstairs and downstairs. off each 1 inch supply it splits off into 3 3/4 loops series loops i assume."

This sounds like a proper piping design for the amount of BTU the boiler has to give you, almost. If you look at the first few pages of the Zoning Made Easy booklet, you will see a pipe size to BTU capacity chart. The 1-1/4" pipe can move up to 140,000 BTUh when there is a 20° temperature drop (∆T). Since your boiler can deliver 168,000 BTUh, there are 28,000 BTUh that can't fit in the 1-1/4" pipe unless you do some changes like move the water faster, which may be noisy, or a higher ∆T.

So to determine the needed pump head, you take the loop with longest run of pipe. Now if you have a 2200 sq ft. home. Lets say that there is 1100 SqFt on each floor and each floor's dimension is about 30' x 40'. the boiler is at one end of the basement. The longest run of baseboard goes from the boiler. The riser is about 5 feet to the basement ceiling.  Then it goes to the front of the basement about 14 feet, then 39 feet to the other end of the basement where it turns to go up to the second floor. That takes about 14 feet to get there. Then that zone wraps the baseboard with ¾” tubing around the far side of the house for 29 feet and turns across the back of the house another 20 feet. Then it drops down to the basement for another 14 feet. Once in the basement it will return to the boiler room across the back of the basement about 19 feet.  At the back of the basement it turns to the boiler for about 13’ the turns down to the boiler return about 8 feet. That is a total of 180 feet if you count all the 8” drops and risers from each baseboard as it jumps from room to room. 

Here is an illustration of that loop:

Now here is an easier way to do that calculation.  House dimension is 30 x 40.  The total perimeter is 140 feet That's the round trip around the house.  There are 2 risers from the basement to the second floor at 14 feet each 140 + 14 +14 = 168 feet. Now add the near boiler piping at about 12 feet and you get a total of about 180 feet of total piping round trip.  There is the first number you need for the rule of thumb calculation 180 feet.

180 x 1.5 for additional fittings = 270 total equivalent length of pipe.

Multiply that by 0.04 for noise free operation, and your pump head is 10.8 or just about 11 feet of pump head. So look for a pump that can deliver 17 GPM for 168,000 BTUh at 11 feet of head.

The Taco 0012 looks like the pump I need for my hypothetical 2200 sq ft house. The Taco 007 falls short by a lot.

You need to measure your longest run to see what you require.

Another reason to select the 0012 pump over a 0011, 0013 or 0014 is because the pump performance curve ofthe 0012 is so flat.  Think about it this way.  When you have a zoned system and one of the zone valves is closed then you only need to move enough GPM for the smaller load of one zone.  That might be about 8 gallons per minute when only one zone valve is open.  Look at the head of the 0012 when it is only pumping 8 GPM.  Compare that to the pump head of the taco 0011. That pump will move 8 GPM with a pump head of more than 20 ft. That much extra power may actually move the water thru that single zone too fast and you will have noisy operation and poor performance.   The amount of pump head increase from 8 GPM to 17 GPM is very little on the 0012.  This is a great pump for zoning.   .

we still haven't seen the boiler. in 1980 it probably came with an 007 installed on the return.

if you follow that over to the 007 curve that is like 3 gpm although since the building is short and tall the head for the first floor is probably a lot less than the estimate. i would think the shortest zone would heat, it just wouldn't have enough flow for all of the zones but we'd need more information. an ecm pump that fits the head and flow is still the way to go because you can set it to multiple curves and it uses less power.

The OP stated that the boiler is 168K btu/ hour output

You need 17 gpm and an 007 will not even be close to moving enough water.

The 007 runs out of gas at 4' of head which is 1.73 psi differential across the pump.

Not going To work

My point is that you are sizing for a guess at the worst case loop, if there are closer loops with several parallel branches the head on those will be much less and those should heat quickly.(I suppose the longest loop method oversizes the circulator in the same way the simplest gas piping calculation method oversizes. you need to cover the head of that longest loop, but you don't need to cover it at 16 gpm, you probably only need to cover it at 4 gpm or less but then you need to figure out how much of that curve the other loops need.)

We need the OP to roughly sketch out the system with rough measurements and pipe sizes to figure out if the only heating by the boiler makes sense with the 007 or if there is something else wrong.

i'm not arguing at all that it is the right circulator, i'm just saying that unless all of the loops are that long and small pipe, some of them should be heating.

monoflo is a different beast. it is one loop with a lot of splits and recombinations in it, if you don't have enough circulator to overcome the resistance of the whole loop nothing will heat. here, from the limited description we have, the water has a lot of paths with a lot of different resistances

A B&G 1-1/4 Monoflo tee has an EL of 25' of straight pipe. So that adds up quickly for calculating pressure drop.

Also heat emitters are in series in a Monoflo tee system, so the end radiators see much lower SWT. Two reasons that they may need more pump power.

Not enough data to calculate what circ will get the job done. But that is a common thread around here :)

So, since 1980 it has never heated adequately?

It would be interesting to check the date code on the 007 maybe it was installed as an incorrect replacement along the way

Or it has worked fine and the system is air locked or the circ is not functioning ?