Maybe I lack perspective that experience in the field would bring. I am concerned that if I don't fix my static that I will shorten the life of my equip and not get the air flow I want. I copied two of the posts that suggested that this is true. I would certainly be less worried if lots of systems have similar static pressures without problems. I have also seen a post on this site that said that the watts used by a VS blower goes up significantly with an increase in static pressure. If a VS blower goes out I believe that the repair could be costly. I am hoping that if I do this correctly I may save myself future headaches and expense. I value your advice as you seem to very knowledgeable.
Registered: Apr 2005
Your static is way high! 0.5 WC inches is the maximum design recommended on the plate in most furncaces. YES, high static can and will shorten the life of your blower and your A/C coil and compressor. Think of it this way, your blower is pushing about double the force of air it was designed for. Therefore it draws more Amps and causes the windings to get hotter than designed to handle.
It sounds like you're going to need about double the duct size, especially the return. A qualified contractor should be able to use the Ductalator to figure what size the ducts should be based on the CFM requirements you're looking for. A Manual J should be performed to determine the room by room CFM requirement and then a Manual D to determine the duct sizing.
Good Luck to you.
"Saving the World One House at a Time !"
Registered: Aug 2002
Originally posted by heetseeker
Static on the supply was measured at the top of the plenum. To me this means that it was above the A coil. Should the pressures have been measured between the blower and the A coil? The a/c also was not running. As I understand it pressures would be higher if the coil was wet. Am I correct? What is your concern about the pressure measurement?
Won't a larger blower further raise my static pressure?
As you said it may be hard to find someone who will fix my system. Any specific training or credentials that I should look for?
Yes ,your reading didn't include the ESP of the wet coil,likely at least .3" wc,and that's if it's clean.The wet coil is only applicapble if the cooling cfm rquired is greater then the heating.
A larger blower,if possible in your situation,would deliver the correct amount of air,at a higher static,as yours can't be delivering the correct amount now.I doubt that idea would work but it may be possible.
NCI as suggested is a good place to start,if not there call around and ask specific question before paying anyone to come out.
The duct system needs to be reworked to lower the ESP.
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[Edited by heetseeker on 06-01-2005 at 10:39 PM]
Since it turns out I'm arguing with Mike, I'll address him.
"0.5 WC inches is the maximum design recommended on the plate in most furncaces"
That's absolutely true. But it bears no resemblance to reality. I'd bet that less than 2% of all systems that have air conditioning actually achieve a .5" ESP (Some of that 2% would by my systems BTW.). You can design a system to meet EVERY single goal you have at higher statics of .6", .7" and even higher.
"high static can and will shorten the life of your blower and your A/C coil and compressor"
High static can shorten the life of a VS blower if you push it too far. But any VS blower can handle ranges well above .5" and live a long and happy life. High static hasn't got poop to do with your coils life. That's just straight out of left field. And high static will not kill a compressor by itself. It's low airflow that hurts a compressor. You can achieve the recommended airflows at low, medium or high statics.
"your blower is pushing about double the force of air it was designed for"
What a VS blower is designed for is not one single number. Trane engineering books give me blower performance numbers for statics ranging from .1" to .9". If the furnace wasn't designed for .9" then Trane wouldn't give me data for .9". Focusing on that .5" number when you have ducts buried in walls that can't be upgraded will do nothing but give you headaches. It's an unrealistic goal.
I'm not extolling high static as a virtue. But it can be worked with.
Upgrade the ducts as best you can and let a powerful enough blower handle the rest. If the ESP is at .7 or .8 then relax! A VS or standard blower can handle that no problem and with a long life. If they (whoever they are) insist that it can't and if you believe them then VS blowers are crap and you shouldn't buy one.
I wanted to thank you for answering my questions. I always wenjoy your answers.I always find your comments interesting and and insightful.
I feel better about the ESP concern I had.
(Don't forget to peruse my site.)
I thought your site was the best I have seen on the web.
Great advice. Only problem is finding someone who does things the way you say they should be done. I have looked at a lot of contractors. Not one does all their work the way you recommend. When I ask the questions you pose on your site they don't seem thrilled to be asked those questions.
In some ways ignorance is bliss. I would probably feel better about choosing a contractor if I had never discovered this forum or your site.
LOL. Too funny. I've caused consternation for both contractor and homeowners alike. Excellent.
I already forget where you're at. But keep in mind my 31 point list is geared towards dry climates. Much but not all applies to other climates.
Here `s a good one for you john,i needed a spec. sheet on pressure drop on evap. coils.I go to supply house tell them what i want, the guy there says" WHATS THAT" I tell him, he says we don`t have any & you don`t need them anyway.
It's not nice to confuse the warehouse monkey like that bigbird. :^)
The thing that got me was he was the factory rep.
That's funny. Usually "lol" is more figurative than literal. But I chuckled for real when I read that. It relates to that old saying "It's funny because it's true.".