Greenwood 200 - Not enough heat in the house

[thuffy]

Flat plate hex IMHO do not work well on wood boilers for a number of reasons. Air locks, improper hook-up/positioning, equal flow, deposit build-up etc. Ditch the plate and line it right in to your boiler. Also make sure the ID of the pex between GW and existing furnace is at least 1" for a GW200.
Good Luck

Cannot hook the GW in to the existing boiler because of a pressure issue. the existing boiler exceeds the Gw maximum allowance that is why we need the heat exchanger. the ID of the pex is 1". Thanks,
tom

1" pex under what is considered normal design conditions is good for an average 80,000 btu output, 100,000 would be maximum. You just can't flow a lot more water through it than that. You probably have two main issues that are unfortunately quite common. The HX is undersized and you maybe should have used 1.25" pex for more flow.

Under normal engineering standards you would see the following temps on your HX. Wood side in 180*, wood side out (back to the Greenwood) 160, House side return 150ish, house side supply 170 or so. What are the actual readings on yours?

I just visited a guy with a lack of heat complaint. His installer used 220' of 1" pex to supply a 30 plate HX. The owner has approx 3,500 sq ft of heated space plus two indirect water heaters. The temp drops on the heat exchanger were much higher than I just described which would indicate not enough flow and heat transfer area. His CB Classic spends a lot of time idling even though the system will only maintain about a 60* differential from indoors to out. He did not like what I had to tell say about his installation.

Readings are as follows:
171 from the GW, 156 into the HX, 155 coming out of the HX and 155 going out to the rooms of the house.
returning from the rooms is 140 - 147, 141 returning to the HX, 152 coming out of the HX and 140 returning to the GW.
Thanks,
Tom

 

[LeonMSPT]

I was going to ask, "How do you guys get 200,000 btu's through a 1 inch pipe?" It has always been my understanding, though I am not entirely sure why, that 90/100,000 was about all a 1 inch pipe would handle.

I know someone with a small greenwood right now. Buried 100 ft of 1 inch PEX from the garage to the house. The GW goes up, shut down, goes up, shuts down, goes up, shuts down... creosote running across the floor, Major mess... going to send the darned thing back.

Solid fuel guy installed and piped it, per his own design.

To me, 100 feet of 1 inch PEX can't handle moving the heat from the boiler to the house. The boiler is working as it is supposed to, but can't "RUN", because the heat can't get out of it. Between the limitations of the 1 inch line, and friction loss... not sure it would move much more than 70K... leaving a 200K boiler choking to death on it's own heat.

I've got a 90,000 BTU add on, twenty feet away from my oil boiler. It's connected with 1 and 1/4 inch steel. Want the heat to move NOW.

Money's no object, best fix is dig it up... replace it with bigger pipe. Other option is, bury another 1 just like it, use 1 pair for supply and the other for return. Connect each pair to a 1 and 1/4 inch header, then the header to the HEX.

No promises on half measures... two 1 inch lines is not a 2 inch line... it's maybe inch and a quarter to an inch and half, don't have time to do the math now. Less friction loss...

 

[LeonMSPT]

According to my Fire Protection Hydraulics coursework, although it's been a couple years...

The longer the pipe, the higher the friction loss.
The smaller the pipe, the higher the friction loss.
The higher the pressure, the higher the friction loss.

Pushing water at a higher velocity through the pipe increases friction loss, and you reach a point of diminishing returns. If the water isn't in contact with the heating surface of the boiler long enough to absorb the heat, it won't absorb the heat.

Worth consulting a trusted engineer, or other source, for specific piping needs based on heat load, source, demand, and specifics like height differences and distance, on designing and installing something that costs a half a year's pay.