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[clydem]

 Adding a unit heater to my existing system. The problem is the new heater has only ½” feed headers and my system is plumbed with all 1” Pex.
When I put the system in it had no manifolds just 1 continuous loop from the OWB – Side arm water htr  – Modine htr – return to OWB all are plumbed with 1” pex.    (The outlet of OWB is ¾”)
If I add another unit heater to the loop that has ½” feed & return lines how will that affect the performance? 
The existing system has a 7* to 10* temp drop to & from OWB. If I add the heater with the smaller  ½” feed & return lines will put more load on the pump?  I realize it will take another 10* out of the water but what other affects am I missing?
Thanks
Clyde

[RSI]

With only 1/2" lines you probably won't get enough heat at any of the heat exchangers. If you are going to use it I would put it on a secondary loop. Put two tees in the 1" line. Run a loop to the modine to the tees. You will need a pump just for the modine but it can be turned on with the thermostat instead of running all the time.

[clydem]

Would I put both T's in the feed line or 1 in the feed and 1 in the return?

Thanks for the reply

Clyde

[RSI]

Both in the same line. Can be supply or return line depending on what is easiest and what has the highest temperature requirements.

It is pretty much just re-directing the water flow at the rate the modine can handle without restricting the main loop.

[clydem]

Do I need to have a valve in between the 2 T's to throttle the flow to the new heater?

thanks
Clyde

[RSI]

No, just a pump in the secondary loop. It will pull all the water it can get. If you do a valve and no pump it might work but will really restrict the flow on the whole system but not as bad as trying to put it in series..

[clydem]

I have a 05 Taco on the owb should I use the same size pump on the branch circuit?

thanks
Clyde

[RSI]

I would put the 005 on it and get a new 007 for the main pump. (or a Grundfos 15-58)