Grundfos 26-99 FC

[Bwhunter85]

Just purchased this Grundfos 26-99 FC to replace the burnt out Taco 007. I'm thinking the upgrade will push more heat and be more efficient. 1" Pex, ~175ft round trip loop to plate heat exchanger on DHW and forced air exchanger on furnace.

 

[E Yoder]

That's a big step up in size (I think about 10' head up to 30'-ish), the good thing is it's a three speed so if you don't need the flow you can run on low speed and save electric. You could measure air temps running each speed, and run on the lowest speed that gives the air temps you want.

 

[Bwhunter85]

That's a big step up in size (I think about 10' head up to 30'-ish), the good thing is it's a three speed so if you don't need the flow you can run on low speed and save electric. You could measure air temps running each speed, and run on the lowest speed that gives the air temps you want.

Yeah, I think the Taco 007 wasn't keeping up with flow very well at the big of a loop and single speed pump. House could barely keep up to temp and forced air furnace blower would run constant during extreme cold trying to keep up with thermostat settings. Be nice to be able to pick from 3 speeds.

 

[E Yoder]

Sometimes the air handler blower is multispeed. If it's not on high turning it up can help.

 

[jebatty]

You will push more heat, but the real issue you have is how much heat (btuh) do you need. A typical wood boiler hot water system is based on a 20F temperature drop :DTT) from supply temperature to the heat emitter and return temperature from the heat emitter. The calculation for btuh is: T x gpm x 500. Next you need to calculate the pump head at the required btuh flow rate to determine what circulator can deliver the needed btuh. Assume you need 100,000 btuh.The required flow rate is: 100,000/20/500=10 gpm. If you need 140,000, the flow rate is 14 gpm. The flow rate changes if the T is different than 20F.

Next is pump head. 1" pex ID is 0.863". Assuming 175 feet of pex and not adding any pump head for your plate heat exchanger on DHW and forced air exchanger on the furnace, pump head is about 31' at 10 gpm, 20' at 8 gpm, and 16' at 7 gpm.

Then, the pump curve for the 26-99 shows that this circulator cannot move 10 gpm at any speed, but it can move 8 gpm on speed 2, and that's about the maximum flow rate you can achieve. Keep in mind that your actual pump head is greater because the added head from the plate hx and furnace air handler plus any additional components (elbows, valves, etc.) are not included, so your actual flow rate will be less.

Finally, at 8 gpm your delivered btuh at T=20F will be 80,000. The good news is that this will be an improvement over the 007 circulator which would have a flow rate of about 5 gpm (50,000 btuh). In both cases actual flow rate will be less, and actual btuh will be less, because of the pump head not included in the calculation.

 

[E Yoder]

I would add that in many cases especially with forced air the delta t can drift up in the 30-40 ° range and still heat well, allowing more btu's per gpm.

 

[Bwhunter85]

You will push more heat, but the real issue you have is how much heat (btuh) do you need. A typical wood boiler hot water system is based on a 20F temperature drop :DTT) from supply temperature to the heat emitter and return temperature from the heat emitter. The calculation for btuh is: T x gpm x 500. Next you need to calculate the pump head at the required btuh flow rate to determine what circulator can deliver the needed btuh. Assume you need 100,000 btuh.The required flow rate is: 100,000/20/500=10 gpm. If you need 140,000, the flow rate is 14 gpm. The flow rate changes if the T is different than 20F.

Next is pump head. 1" pex ID is 0.863". Assuming 175 feet of pex and not adding any pump head for your plate heat exchanger on DHW and forced air exchanger on the furnace, pump head is about 31' at 10 gpm, 20' at 8 gpm, and 16' at 7 gpm.

Then, the pump curve for the 26-99 shows that this circulator cannot move 10 gpm at any speed, but it can move 8 gpm on speed 2, and that's about the maximum flow rate you can achieve. Keep in mind that your actual pump head is greater because the added head from the plate hx and furnace air handler plus any additional components (elbows, valves, etc.) are not included, so your actual flow rate will be less.

Finally, at 8 gpm your delivered btuh at T=20F will be 80,000. The good news is that this will be an improvement over the 007 circulator which would have a flow rate of about 5 gpm (50,000 btuh). In both cases actual flow rate will be less, and actual btuh will be less, because of the pump head not included in the calculation.

Thanks for the in-depth response! So I should see more heat out of the system by upgrading the pump? What would happen if I out in a speed 3?

 

[jebatty]

You will get a little more flow. Pump head on 175' of pex and 8.75 gpm is about 24'. The pump curve for the 26-99 shows on speed 3 the flow will be about 9 gpm at 24' of head. Again, keep in mind that your actual pump head is greater because of the added head from the plate hx and furnace air handler plus any additional components (elbows, valves, etc.) are not included. Pump head rises rapidly as additional equivalent length is added due to these items which are not included in the calculation.

The fundamental issue you face in trying to get more heat is that 1" pex is undersized for the distance you want to move the hot water.

 

[E Yoder]

If/ when you swap circulators a good experiment would be to run the heat with the 007, recording the difference between supply and return water temps (delta t) and air temps at the registers in the house.
Then switch to the 26-99 and do the same on each speed.
Then you'll real numbers on how much benefit v. electric cost you have. I'd like to see them.
It's a possibility the heat exchanger (coil) or air handler size may be part of the issue too. Those numbers could help pinpoint the bottleneck.

 

[Bwhunter85]

Hooked up the new pump, you can feel the difference in power from the old Taco 007. Actually feel the water running through the lines. I'll be happy once I start it back up this fall and can mess with the speeds to see what is best.

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