More efficent ducting

The answer to my question is probably on here already but i cant find it yet. I have a keystoker a90 furnace set up right next to my propane forced air furnace. I have a custom plenum on top ducted directly into the plenum on the propane furnace. the cold air return is blocked off at the filter so it is redirected to the coal furnace blower. the system works but the coal furnace blower gave very little air flow though the ductwork. I tried a larger blower that helped a little but not alot. If i run the propane blower it overpowers the coal blower. I believe i can fabricate a new plenum on the coal furnace to duct into the cold air return on the propane furnace and let the propane blower pull the air in then out but i dont want to go through all that if it wont help much. Anyone know if this would work better. Thanks

Thanks it is a keystoker furnace and there is a cold air return that i fabricated from the propane furnace return.
Im at work tonight ill try to get some pics tomorrow

Here is a series duct arrangement along w/ some valuable guidelines:

Conversion of a Riteway #37 into a Stoker Furnace

ed,

You have connected the supply of the Keystoker to the supply on the propane furnace? The fan on the a90 hangs on the outside?

If so, could you install a larger squirrelcage fan on the a90? Not hard to find those good-used from old furnaces often laying around at most residential / light commercial HVAC contractor shops.

That said, as you mentioned, tying the a90's supply into the the return side of the big furnace would be best [imo also].

Dave

Thx doug, yes the keystoker is tied into the supply plenum on the propane furnace, i did replace the blower on the a90 with a large squirrrel cage blower, had to modify a tapered adapter to make it fit the opening, and that helped some but still way short of where i feel we could be. I think i will try tying it into the return side of the propane furnace and modifying the return above the tie in to get the cold air return to the blower onthe a90. i talked to coalway yesterday and their installer is going to try and stop by and help troubleshoot

Does your keystoker not keep up with heat demands?

I was used to hearing and feeling the WA furnace fan as well. When I installed my boiler and air handler I originally thought there was no way that could work when it got cold outside. I can just about feel air coming out of my vents from the blower, it's that slow and quiet.

It's a balmy 8°F out this morning and steady 72°F here with my coffee. Even at well below 0°F we've never been without sufficient heat and my house is not an energy rated home either. The nice thing about slow air movement is some of the dust is cut down and like heating with a stove, everything around you gets warm rather than just a blast of hot air for a minute or two then a draft.

Just wanted to throw my $.02 in. May not be of value to you but sometimes a different opinion can alter our thoughts just enough to have a eureka moment.