Outdoor wood boiler installation

I have some question about insulated pex pipe sizing. My father-in-law has an outdoor wood boiler, it is rated at 250,000 btu/hr and is located about 130 ft from his house. the installer used 1" pex to plumb it to a water to water heat exchanger which keeps his oil boiler up to temp. they used a taco 009 pump at the owb to move the water. the boiler is located up grade from the house i estimate it would be about 15' of head for the 009. my question is, should the installer have used larger pex? i know the 009 is capable of handling the head. but at 15ft i think it pumps in the range of 7 gpm. is that enough flow to get enough btu's to tthe house? also could that be contributing to an over temping problem he is having on warmer days ~65f.

The tubing size would not contribute to the house being too warm. That might be caused by ghost flow in one or more zones in the house...feel for warm pipes when there hasn't been any heat calls for a few hours.

As for the pex size and circulator choice, if the system can keep his house warm all winter I would leave it alone. Larger tubing may have allowed the use of a less powerful circulator, but it is too late for that now.

250k btu rating...that is usually an unreachable output in real world use. Outdoor wood boilers quickly get a thick coating of creosote in the boiler, and often run around 50% efficient.

Head is actually not related to lifting height. A three story home and a single story home will have the pump seeing the exact same head if the piping lengths, diameters, number of elbows, etc... are otherwise identical. Head is therefore a product of only these things. I.E., pipe diameters, lengths, elbows, tees, valves, etc. Height does not enter into it.

I believe that to move 250,000 BTU's of output per hour requires 25 gpm of flow, and I believe that calls for 1.5" I.D. black iron pipe. For PEX I don't know what would be called for.

BTU's = GPM x 500 x delta_T (where delta_T is generally assumed to be 20 degrees of overall temperature drop across your baseboards or through your radiant floors)

Therefore: BTU's = GPM x 500 x 20

Rearranging for GPM you get:
GPM = BTU's / 500 / 20

Then solving for 250,000 BTU's gives us:
GPM = 250,000 / 500 / 20
GPM = 25

25 GPM of flow will deliver 250,000 BTU's at the standard 20 degree temperature drop, meaning that if the water departs your boiler at 180 degrees and at 25 GPM of flow, and then it returns to the boiler at 160 degrees, 250,000 BTU's per hour are being delivered somewhere.

Since you don't know the actual head of your system, you can't look on a pump curve chart and know how many GPM's your circulator is actually delivering, and therefore you can't calculate your pipings maximum potential to deliver BTU's.

I don't believe a Taco 009 can achieve 25 GPM at any head. A Taco 0012 seems like it has this potential at up to about 10 ft. of head.

Since the elevation of the hot water supply and return are at the same level, the height of the boiler has no bearing on pump head. It is stricly pipe losses.

I figure 1" pex is limited to about 7 gpm before the pressure drop becomes excessive.

Depending on system design, a 20 to 30 degree temperature drop is the reasonable limit. There for max btuh on 1 pair of 1" lines would be approximately 7 x 500 x 30 or 105,000 btuh.

Pex larger than 1" gets expensive. Typically, if more load needs to be handled, the mutiple pairs of 1" lines are run.

Thank you for all of the reply's so far. i have not had a chance to read and digest all of them but, i would like to clarify that when i mentioned over temping in my OP i meant that on warmer days his owb over shoots the set point of 180f water temp and boils water out of his unit. i suggested to him to maybe lower his set point and open some windows on warmer days that he does not want to shut the owb down.

Sounds like the boiler is getting to much air when it is supposed to shut down. I have seen many of these units in E. Maine and they will literally put the fire out if the temp is high enough for long enough.

Kevin

Boots wrote:Thank you for all of the reply's so far. i have not had a chance to read and digest all of them but, i would like to clarify that when i mentioned over temping in my OP i meant that on warmer days his owb over shoots the set point of 180f water temp and boils water out of his unit. i suggested to him to maybe lower his set point and open some windows on warmer days that he does not want to shut the owb down.

go here

http://www.hearth.com/talk/threads/simp ... ign.16567/

read about and add energy storage -- something Coal boilers do not need as they store excess energy in the black rock they burn