trying to fix a botch job install - woodburning boiler system

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Old 11-07-12, 10:25 PM
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trying to fix a botch job install - woodburning boiler system

I have an Aquatherm 275 wood burning boiler.

It's 135 feet away from the house.

When they ran the water lines through the basement floor, they reduced the 1" id pex-al-pex to 5/8"id white pex for a 76' loop , connecting first to the water heater side arm exchanger, then to the 16x18 water to air exchanger, then to the 1" pex-al-pex return line to the stove.

So, stove to house loop: 272' of 1" pex-al-pex.

Inside house to side arm exchanger and water/air exchanger loop: 76' of white 5/8" id pex. The run of 5/8" pex in the house has 10 elbows in it.

There's one Taco 007 pump on the back of the boiler.

How do you determine the gallons per minute flow I have now?

When the temp drops below 0, the boiler doesn't keep up, house drops down the 50 degrees if I don't turn on the fuel oil furnace.

I'm told I need to replace the Taco 007 with a high volume pump.

What gallon per minute flow do I need, and what would the total head feet be in the setup I've got?

All and any advice id appreciated.
 
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Old 11-08-12, 08:13 AM
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How do you determine the gallons per minute flow I have now?
Compute the total equivalent length of straight pipe - along with that, the pipe size, and internal roughness of the piping material. Then you plot the head loss for different assumed flow rates, and graph that on the pump's head-flow characteristic curve. The intersection is the operating point of the system.

Another way is to install a calibrated orifice somewhere in the piping system, and measure the differential pressure across it. Or, measure the differential pressure across the pump, pick that point off the pump curve.

The short answer, is that most of us mere mortals can't solve the problem. There are computer programs that can help (Google "flow in pipe calculations")

What is the Btu/hr rating of the wood stove? What is the caculated heat loss for the house? If the stove rating is less than the heat loss, then you aren't going to be able to heat the house on the colder days with the wood stove.

You could easily replace the Taco 007 pump with a 0012 (equivalent to the Bell & Gossett HV series). The next step would be to start replacing the pipe in sections with larger pipe.

Won't you get tired of walking 272' out and back to the wood stove in the winter?
 
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Old 11-08-12, 03:25 PM
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Here's another approach to estimate your flow if you are good with numbers. Note that the pumping power delivered by the pump is equal to flow rate multiplied by the head across the pump. That gives you another equation to plot on top of the circulator's characteristic curve - where they intersect, that will show the flow rate.

To estimate the shaft electrical power of the pump's motor, measure the motor amps and voltage. VA multiplied motor efficiency and motor power factor gives you the shaft power, in watts. You can assume both are 0.86. So power = VA x 0.86 x 0.86 = VA x 0.74 (watts)

Convert from watts to gpm x psi, and plot the equation for the power curve.
 
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Old 11-08-12, 03:50 PM
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The wood burner

Are you shure there is a minimal heat loss in that 135" X 2 between the house and the boiler? Is the system protected from freezing if you get 2 or 3 feet of snow, and can't get out right away? Just asking.
Sid
 
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Old 11-08-12, 03:58 PM
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Here is the manual: http://www.aqua-therm.com/aquatherm_manual_010109.pdf

Is your unit installed in accordance with the manual? Your unit is rated 80,000 Btu/hr. Tell us the temp differential between the supply and return at the wood stove . Depending upon the insulation, you might me losing half or more of the stove's heat ouput through the lengthy piping, which would put the net output at 40,000 - pretty puny, depending upon your location and the house itself. I'm guessing that your stove is just too small, combined with the piping losses.

What is the Btu rating of the oil-fired boiler that you have to use during cold weather?
 
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Old 11-09-12, 09:19 PM
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I think the pump is too small for that length of tubing, etc... but that's just a gut feel not backed up by numbers.

I also agree with gilmorrie that you may be losing a lot in the tubing.

A bigger pump may help, but not solve the problem.
 
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