High water flow

hrlevy

I have just installed 2 old Fedders hot water unit heaters in my garage. The BTU rating is not listed. The size of the radiator core is 16"x16"x2". It seems that the air leaving the unit heaters is not hot, it is just warm. I was wondering is it possible that I have too high of water flow through these units. I am using 00R 3 speed pump on this zone. Water temp is 140 entering unit, 135 leaving. The fan motor are old but still move a lot of air. If I keep the fans off for a few minutes the air is hot at first then goes back to being just warm.

CMadatMe

You Anwsered

Your own question. Not transferring any Btu's on a 5 degree

Delta-T. Assuming a 3/4" supply/return



4gpm x 5 x 500 = 10,000 btu/hr



I used 4gpm for the max flow rate for 3/4" copper pipe.

hrlevy

Still confused

System is piped with 1" copper feeding into 2 feeds of about 20' long of 3/4 pex-b lines one for each unit. I have had the radiators in both units "cleaned" by a radiator shop. I understand that 5 degree Delta-T is not enough, but I still need to know why I am I not getting hot air from these units. Lowering the pump to lowest speed has minimal change. Is the water moving too fast to transfer heat to the radiator cores? Shouldn't a core this size be able to transfer more heat than just 10,000 Btu? What other changes can I make to get more heat out of these heaters?

CMadatMe

If You

Understand that a 5 degree delta is not enough then what more is there to understand? You can only get what you give.



If i get my delta to 20 I get.



4gpm x 20 x 500 = 40,000 btu/hr thru that same 3/4" pipe. More then likely a little more using Pex. Your over pumping!!!

SWEI

physics

In order to increase the LAT, you basically have two choices:  Lower the airflow rate or increase the average fluid temp.



What fluid temp are you running?  I suspect those unit heaters were designed for at least 180F.