Static pressure breakdown

[mike_meridian]

I have been using a magnehelic gage to measure static across furnaces and comparing it to the nameplate to divine the condition of that hard to get to coil.

Sometimes the negative portion of the drop is greater than the positive, sometimes the positive is greater, and once today is was an even split.

So, what does it mean if you got a 0.25WC on the neg side and a 0.10 on the positive, or vica verca?

Thanks,

Mike

[davevava]

Is this a Furnace or AH?

[mike_meridian]

It is usually a remote gas furnace, with a coil on top.

I use the terms AH and remote furnace interchangeably. Is this wrong too?

Thanks,

Mike

[dash]

Furnace is a furnace,with or without a cooling coil.

Air Handler ,most often has a cooling coil in it's cabinet,and coil is under negative pressure.

The return or supply static being higher or lower,means little,as long as the total is with the capabilities of the furnace/air handler to move the required air.

There are some exceptions,one is very high static on the return of an air handler,can cause water to be pulled off the coil,during cooling.

[mike_meridian]

I must see mostly furnaces with cooling coil because they are upflow with the fan on the bottom with a coil added on top, but sometimes in the cabinet.

Would a horizontal unit in the attic or crawl space be more likely to have a true air handler? So are you saying that the key characteristic of a air handler is that the coil is under negative pressure, and does it matter if there is a heat bank or heat exchanger?

Thanks for the clarifications.

Mike

[canesfanforlife]

Static pressure should ideally be around 0.5-in wc -0.7in wc External Static Pressure. The difference between - and + press. can only help diagnose where there is a problem.(return/supply)

Also a furnace has gas or oil running to it. An air handler only has electricity going to it. Helpful Hint:cool:

[dash]

Like stright cool with electric heat or a heat pump!

[davidr]

Static pressure should ideally be around 0.5-in wc -0.7in wc External Static Pressure. The difference between - and + press. can only help diagnose where there is a problem.(return/supply)



Be sure and check the manufacturers fan data before making this assumption.

There are quite a few pieces of equipment out there that cannot produce airflow at 0.3" TESP.