Wood Boiler: What Setting On Circulator Motor To Use?

[StihlRockin']

As the hose comes into my basement through the foundation blocks from the stove/boiler outside, there is also the lowest part of the hose, so that is where the motor sits. This motor circulates the water into the heat exchanger back out to the boiler and back again. There are 3 settings on the motor. Most likely meaning slow, medium and fast.

What setting do you think I should have it on? And if you suggest a certain setting, why?

The boiler holds 175 gallons of water. The thermo on the stove to the fan shuts off when the water temp gets to 172° and turns on again when it reaches approx. 150°.

StihlRockin'

 

[windthrown]

I never used a variable pump for the main loop in an OWB, or inside the house for the hydronic floor loop for that matter. Taco pumps are on or off. I would set it on high, for the most circulation to get the most and fastest heat out of the boiler. Having the pump at the low point in the loop is good, as more pressure will lessen the likelihood of pump cavitation (if it is an open system). For MN, your stove setting seems low. That temp range worked in mild Oregon, but I would think you would run it higher, between 180°/160° there. It will likely overshoot and undershoot... 10-20 degrees, depending.

 

[Mike Van]

When you change the pump speeds, keep an eye on your temps - I actually lost 10 degrees by going to the hi setting. Not enough head pressure. Went to low and lost 2 degrees of the 10 back, so it's on medium from here on out.

 

[ash man]

Mines on medium to the house and seems to do a good job. I have another pump on the owb going to an outbuilding and its set on low, because I only want to keep it above freezing and circulate water through 2 old cast iron registers. My water temp is 175 and turns back on at 168. On warmer days that 20° difference seems like a lot. Jmo

 

[StihlRockin']

The last 2 years the setting has been on high, then this year I turned it to medium.(no reason why) As for the temperature on the stove, it still shuts off at 172° and turns on at around 150°. I wouldn't think this would change as I'd assume it's a setting with the thermo.

Two observations I've made this year about the stove are below:

** Whenever I go and check the wood, I always check the temperature and it seems the water temp is mostly closer to the 150° mark than the 172°. This could be purely coincidental.

** It appears the air coming out the floor air ducts is cooler, which could be a result of the water temp actually being closer to 150°, and not a coincidence. Hence it seems it takes longer to heat the house and the fan runs longer.

But of course, that may be due to the below 0° temps we have on average lately.


Thank you very much for your advice, opinions and help in this matter. Each tidbit of advice I can get is a plus!

StihlRockin'

 

[windthrown]

The low temp of the loop and air duct means the boiler is struggling to maintain temps. 175 gal. system is pretty small. I would set the thermostat in the boiler higher to at least to 180, or even 185 so that it fires longer and stores more energy in the loop. Even if there is a 20 degree overshoot is will not boil over. I think it is likely that you are just maxing your system out at those low temps and it is staying nearer to 150 all the time. In which case all you can do is burn denser wood that has more energy (like apple, hickory, oak, and locust), or use a backup heat source like a fireplace or electric oil heater to help heat the house in really cold temps.

 

[bayard]

i have a 3 speed pump also on a inside boiler.i do change the speed daily.based on the outside temp.i run my boiler at 185 t0 195 most times.vary the wood locust and hickory at night, lesser wood daytime.

 

[phantomblack]

I'm running a 3 speed b&g pump in 2nd gear for the past two years. I have infloor heat in the whole house, and don't have a problem keeping up in 2nd gear.

I did notice that my return temps to the boiler changed, when I was running a taco 009 return water was 7degrees cooler than inlet water, now it's 4 degrees. That's running with inlet water between 175 and 185.

 

[milkie62]

The ol' CL40 Classic-------180 degree thermostat,its set it and forget it 18 yrs ago and it is still ticking.Replaced the door gasket once (my fault)) and burn almost 10 cord a year.

 

[StihlFroling]

You want to have a 20 degree differential at your emitter/exhangers no mater what the supply temp is. You also want to maintain proper velocity of water thru the pipes, too much causes problems and is not efficient. If you run less than a 20 deg differential you are loosing efficiency and wasting wood. same for excessive flow. So take temps on supply and return of each loop/zone. and adjust speed accordingly. infloor radiant is different , 10 deg is the norm and below 140 depending on type of floor. At the boiler the lower your operating temp the more efficient, longer burn times and more comfort. look up outdoor reset control. Just dont run the boiler below 140-150 or manufacturer min. This is condensing temp conditions. 180 at your house might be the same as 190 at someone elses. theres lots of variables. Pumps will flow more GPM and carry more BTU with hotter water, there are tons of charts on this for every kind of radiation device. ( fin tube, infloor type, cast iron rads,emitters, etc).
I dont know why some thing biggeror faster is better , in hydronics its always worse. 1 GPM flow@ 180deg carries 10,000btuh, so if you know your heat load or have a heat loss calc you can figure things out. If you find a big temp loss between house and boiler, when you have your proper 20deg diff at the exchangers, then you have bad underground lines. Proper loss for underground is >1 degree per 100' at 2ft per sec flow or 4gpm in 1" pex roughly. Running the pump at higher speed hides the temp loss but its still loosing heat to the ground. Logstor/Urecon has good charts on this info and recomended flow rates. Also check out Taco pump site for all the info and troubleshooting you'll ever need.

Mikie62
By the way, nice job on the 18 yr old Central. Love to hear a good story or stove running good. And the fact your on the same pump means it was done right.

 

[StihlRockin']

Wow! That's some good stuff gentlemen. Looks like I have some studying to do. I will also call up the rep. who sold me my unit to see about the temp settings. I also know the manufacturer, so he may be able to help too. I know when it's warmer out, I sometimes can hear the fan motor turn on about 1 1/2 to 2 hrs. When it's cooler out like it is now, it seems 35% to 40% of the time it's running. Plus, I have poor insulation in the ceiling.

Thanks!

StihlRockin'

 

[CBwoodheat]

Did I miss it or did we never get the brand and size of pump being used?

Also pumps vary just like torque in engine builds.
A big pump in some systems will pump less gpm than a small pump with the right pump curve. Others are right with their advice but without knowing the system curve you will always guess at what pump to use and what setting on var speed pumps.