wood boiler flow rate

[hartwa]

Hi Fellas.... I've had this wood boiler for a couple years now but I've never had a flow meter set up on the lines....I picked one up and decided to install it. I was surprised to see that I only have 2.75 gallons per minute running through the lines.

my run from the boiler to the house is 105' and I'm using 1" line...total 210 feet for the loop.

In the basement I got a 30 foot run of 3/4" pex...total 60' loop.

I calculate a head of around 8.5' at 2.75 gmp.

the pump I'm using should be able to do much more....do you think I have an obstruction somewhere?

the pump is a cp3s26 - 110 FC.

what do you guys think am I crazy or do I have an obstruction?

 

[BoilerMan]

Is it boiling over when in operation? I assume its an OWB and unpressureized.

BTW welcome to Hearth.com!

TS

 

[hartwa]

Is it boiling over when in operation? I assume its an OWB and unpressureized.

No.... it's not boiling over. It is unpressurized.

At 2.75 gpm I am getting about 28k btu into the house. I expect I should be getting about 4 gpm with that pump.

 

[tom in maine]

I think you are not calculating the pressure drop properly. In addition to the 1" and 3/4" loops in series, you have fittings.
All this compounds the pressure drop. Your plumbing is way too small for this long a run. You just found that out, fortunately, before something
overheated.

 

[maple1]

No.... it's not boiling over. It is unpressurized.

At 2.75 gpm I am getting about 28k btu into the house. I expect I should be getting about 4 gpm with that pump.

What make/model of boiler? Exactly what kind of pipe underground?

It might not be boiling over - but does it idle a lot?

You may have provided a real world example/observation of OWBs being commonly underpiped.

 

[leon]

Hello to my friend Maple One,

AH yes the dreaded flow rate head loss algebra problem.

I would also recommend that you pour a gallon or two of
apple cider vinegar into the boiler, run it to boiling temperature
and when it begins boiling it will break up any sediment and
then flush it.

It may well be worth the effort of pulling the pump or pumps
and examining the impellers after you boil, flush and drain
the system it to examine them for wear.

Its time for a huge buffer tank in the basement, I hope you have
a Bilco door or a set of french doors to wheel/roll a tank in.

I would use cider vinegar or wine vinegar to break up any possible
buildup and then flush it with a tank of water.

 

[Tennman]

I sized our pump to move 80% of the capacity of the boiler and have a 30*F temp drop (deltaT) thru the HX with 170F water coming in (as best I remember). You've provided the pex diameter and length. If you provide the boiler's capacity and deltaT goal, Monday when I get to work I can compute the required gpm and head per the TD10. Hopefully you have a boiler that's less than a 40 Class, otherwise the flow velocity thru that 3/4" section will be extremely restrictive. Someone else may compute before Monday, otherwise I'm glad to help. Regardless of the results, if it were me, I'd replace the 3/4" immediately. It will pay for itself eventually in your electricity bill.

 

[heaterman]

Hi Fellas.... I've had this wood boiler for a couple years now but I've never had a flow meter set up on the lines....I picked one up and decided to install it. I was surprised to see that I only have 2.75 gallons per minute running through the lines.

my run from the boiler to the house is 105' and I'm using 1" line...total 210 feet for the loop.

In the basement I got a 30 foot run of 3/4" pex...total 60' loop.

I calculate a head of around 8.5' at 2.75 gmp.

the pump I'm using should be able to do much more....do you think I have an obstruction somewhere?

the pump is a cp3s26 - 110 FC.

what do you guys think am I crazy or do I have an obstruction?

I think you have waaaay more head in that system than 8.5 if you're only generating 2-3/4gpm with that pump. It's probably in excess of 25 ft depending on the speed setting. What type and size heat exchanger(s) are in the loop?
Probably no "obstruction" other than the piping loop itself.
Look at the pump curves on this data borchure and note where the head falls at the gpm you're measuring.......

www.stiebel-eltron-usa.com/pdf/brochure_cp3s_pump.pdf

 

[BoilerMan]

No.... it's not boiling over. It is unpressurized.

At 2.75 gpm I am getting about 28k btu into the house. I expect I should be getting about 4 gpm with that pump.

Boiling over is completely possible in a common unpressureized OWB. Lots of steam from the tea-pot is what happens.

TS