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[Firechaser]

I am getting ready to install my Portage and Main ML30 here in a couple weeks and I need to order my heating coils. My question is can I do any harm by oversizing my exchanger? I  have to put my exchanger fairly high into my plenum due to having to be above my A coils. By the time I get above them my plenum widens out and then branches right and left. I figure I need a 130000 btu exchanger for my house ( 2000 foot ranch with partially finished basement). The ones I have seen are 18" x 18". My Plenum is 25"x 25". My question is what if I go with a 170000 btu exchanger? This would make the dimensions closer and be easier to make up the distance between the exchanger and the plenum walls. Is it better to have my exchanger take up the whole plenum or should thier be space arround it for air flow? I am having trouble picturing how to make this work so I will take all the advice I can get. Thanks Tony

[willieG]

myopinion is to fill your ductwork. if you leave a gap around your exchanger the air you move will take the path of least resistance and will mostly flow around your exchanger. my ductwork is also very large, i filled it and my blower has a 2 speed fan and never  gets out of low speed now. I m not a heat and cool expert by any means (there may be a few on here) but that is what i have been told about air flow

[Bull]

It will not hurt anything to go bigger.

[oldchenowth]

My plenum is larger than my HX, I bent a piece of sheet metal at an angle to direct flow into the HX and reduced the area of the plenum.  It also acts as a shelf to set the HX on making it easy to clean if it gets dusty.  If you have the room and it is in your price range I don't see why a bigger exchanger would not be better.

[RSI]

You want to put the biggest one in that will fit.(or that you can afford) If you put a smaller one in and block off the rest it will make your AC less efficient. They come in a lot of different sizes and usually can get one very close to the correct size.

[Airgap]

My plenum is 16x18. So I went with an 18x 20 to fill as much as I could. I just had to bend some sheet metal to make everything work.