Replacing lines worth it?

[HM81]

Curious if replacing current pex lines buried in the ground worth it? How do I figure the heat loss? I have an outdoor wood stove that heats 2 homes, 400ft of line. Buried underground and with Wisconsin winters up and down, just trying to figure the cost of replacing the lines or will really make that much of difference considering cost and time to replace lines.

 

[shawntitan]

Find a way to accurately measure the drop in temperature of the water leaving your stove, and upon its return, with no demand. That’ll let you know if it’s worth the investment. I’m in a warmer climate (NJ) but I only drop a couple degrees on a 75 foot run. Do you have any visible snow melt above your lines? What’s your existing insulation on the lines like?

 

[brenndatomu]

Measure temp leaving the boiler, and then when it gets to the house...1* per 100 ft of line is considered acceptable...so if its a 100' line, and its leaving the boiler at 180, it should be still be 179* coming into the house...then whatever the temp is after if goes through the heat exchanger(s), then that temp would be ok to be 1* less when it gets back to the boiler (again, that assuming your line is 100' long...you will have to adjust your calculations according to actual length)

 

[ewdudley]

Measure temp leaving the boiler, and then when it gets to the house...1* per 100 ft of line is considered acceptable...so if its a 100' line, and its leaving the boiler at 180, it should be still be 179* coming into the house...then whatever the temp is after if goes through the heat exchanger(s), then that temp would be ok to be 1* less when it gets back to the boiler (again, that assuming your line is 100' long...you will have to adjust your calculations according to actual length)

Heat loss can be estimated with the formula:

btu_per_hour = degF_temperature_drop * gpm * 500,

where 500 represents (60 minutes / hour) * (8.33333 lb / gallon).

In the example above that works out to 3000 btu_per_hour = 1 * 6 gpm * 500, using 6 gpm to pick an optimistic flow number. Measuring the temperature drop is critical, the temperature sensors should be measured against one another to correct for error.

That would be about 10% of (for instance) my system load. Does that sound right?