HX in plenum question

[adenowski]

Hi everyone,

Over a month ago I installed a new CB 5036 OWB. Replaced my dad's homemade one, because it was just old and not working good. I have 1" pex from boiler to house, total of about 80' there and back. Then down to 3/4" pex from inside house (basement) to the HX in plenum, about 20' round trip on the 3/4". (Various fittings)

I have a Taco 009 on the boiler, this is rated to 8 gpm. When the house demands heat, I have incoming temp of 180* and returning temp of 155*, so I have close to a 25* drop in temp thru the HX. The HX is an 18" x 20", installed horizontaly in the plenum with the incoming water on the bottom side of the HX and return out of the top of the HX.

Is this a normal temperature drop? The Central Boiler install manual shows the water hook ups with the supply on bottom and return from the top. Is this right?

I don't have the domestic hot water hooked up right now, that will be in the future.

Thanks for any help or comments.

Anthony

 

[leaddog]

You will get more btu's from the hx if you hook the supply to the top of the hx as the air heats up and hit the hottest part of the hx as it exits. A 25* drop is normal.
leaddog

 

[Mid Michigan]

I have almost the same set up as you and my sup/ret temps are always 20 deg. apart with furnace running. Generally the hot water goes in the top of the coil. As the heat is pulled out of the water and it becomes cooler it wants to go down. This helps aid in the flow as the outlet is on the bottom also.

 

[mybowtie]

I have a woodmaster 4400. Instructions and dealer said to put the supply o the bottom
and return on top...Dont have a temp reader, so dont know what kind of drop i'm getting..

 

[adenowski]

See this is starting to get confusing. I been to other sites and herd that people put the supply in the top and return at the bottom to max efficiency. This is why I had to ask here.

Thanks for everyones input, I just want to get the max out of my situation and hopefully help somebody else that might have the same questions.

A

 

[stee6043]

There have been some compelling arguments made supporting the "hot in the top, cold out the bottom" of water-to-air heat exchangers. Ultimately the gains are modest, however. If we had heat exchangers that were 15" deep I think the gains would be much more noticeable. But with our HX's only being a couple inches deep the air really isn't in there for very long, relatively speaking. I run mine counter flow (hot in top) but I really doubt I could measure the loss of efficiency if I were to run opposite....