90% venting questions

[RoBoTeq]

I figured you were lurking Jim How the hell are ya?

Now I'm gonna have to do some testing of my own, which is not as easy as when I was a tech rep with my own lab set up.

Hell, I put in one of the first two stage units made for my sister back in the 70s. It was a Ruud two stage that was eventually discontinued for lack of interest in it. I loved it. The thing ran nearly all the time on low fire and my penny pinching sister raved about how cheap her heating bills had become since I replaced her old unit.

[Jim Davis]

Originally posted by RoBoTeq
I figured you were lurking Jim How the hell are ya?

Now I'm gonna have to do some testing of my own, which is not as easy as when I was a tech rep with my own lab set up.

Hell, I put in one of the first two stage units made for my sister back in the 70s. It was a Ruud two stage that was eventually discontinued for lack of interest in it. I loved it. The thing ran nearly all the time on low fire and my penny pinching sister raved about how cheap her heating bills had become since I replaced her old unit.

Was on the road when this all started. I heard things changed with you. But still enjoy our conversations. As far as your sister I can't imagine how much more she could have saved. I really wish two-stage could be efficient and many more problems could be solved!

[wormy]

Heetseeker

I'd prefer both pipes for your furnace be located away from the dryer vent.

Inlet pipe due to chemicals in laundry.

My reasoning for the outlet pipe is just me being 'overly'
cautious. I run too many "what if" situations sometimes
so I can try to avoid becoming a victim of Murphy's Laws.
i.e. What if Heetseeker moves out and the new owner is the
big time cook that has this huge vent-a-hood installed.
The house ends up in a negative pressure and the easiest place to pull in air through the dryer vent (Sucking air from outside through the clothes dryer). And low and behold, the fumes from the furnace get 'sucked' into the house.
A very unlikely situation to say the least....
But I figure.. If I can think it... it might happen hehe.


Somewhere in this thread, I saw you mention your ducts have high static. How are you determing this?

I sure wished I could come to your house and evaluate the situation.
Bring me up to speed on what you got going on.

[RoBoTeq]

Jim; my sisters old furnace was very old and very oversized so it really didn't matter what I replaced it with, she was going to see a savings.

Now you really have my curiosity up. I like the idea of two stage and modulating furnaces and assume that because they have longer run cycles they must operate more efficiently.

Since I am quite aware of the farsical means that we design cooling equipment to test out more efficiently on the bench, I am reluctant to think you may be missing something.

[heetseeker]

Wormy
Thanks for your replies and your interest. I wish you could see my house too. For my static pressures I had a contractor come out who checked the pressures. Search under my name and see my post on high static pressures.
I have been busy. I took down the drywall in my basement and found out that my 3 supply ducts to the master bedroom are all faulty. The two long runs to the addition to the bedroom were basically disconnected from the main trunk. When they added the flexduct they probably moved the hard duct enough to have the connection to the main run fall apart. The ducts were held together with dried up duct tape.In addition the connection between the hard ducts and the flex duct had big gaps. The third duct to the bedroom has a big air leak where the hard duct meets the supply vent. No wonder the bedroom was cold in the winter. I guess the best solution for this last problem is lots of mastic.
I also found out that one of my wall return ducts was blocked by a piece of metal at the floor after I opened the metal between the joists in the basement . Apparently the original installer when they built the house had tacked up metal to seal the return but forgot to remove it.
This should reduce the return static on my big furnace. The return static on the big furnace was .5 and the supply was .35 the first time they measured it. They came back and when they remeasured it they got the following measurements. There is an open grill on the return drop of the large furnace. we measured the static with the grill open and covered. Unfortunately they had no solution to the static. They said they install lots of furnaces with similar static.


grill open
.18 filter .5 blower .25 A coil .18

grill closed
.26 filter .58 blower .25 A coil .18

The numbers are placed where the readings were taken in relation to the various furnace components. With my limited knowledge I figure my static is normally .83 [.58+.25] since I plan on closing the grills when the furnaces are replaced. With my newly functioning return I suspect the static pressure will fall closer to the .75 that I get with the grills open. I am thinking that if I get a vs 80 2 stage furnace that the static will be lower most of the time when the furnace is running on low fire[altho with less thermal efficiency].
The a/c will still be a problem. I don't really want to go to a two stage a/c because of cost. Can you comment on how bad you think these pressures are?
Again thanks for your interest.

[Irascible]

Why the obsession with static? The measurement of static serves only to tell us what we need to do to get our airflow up to appropriate levels. A low reading serves no purpose unto itself. Proper airflow is the goal. A LOT of systems have an ESP of .8". I'm not saying that's good. It's just a fact. You can get the airflow you need at the pressure and even higher if forced to.

If the ducts literally can't be upgraded due to space limitations then you'll have to embrace the high static and put in a blower that can handle it. If space isn't a limitation then upgrade the ducts. This isn't rocket science. If it seems like rocket science to your contractor then get a new one.

[heetseeker]

Irascible
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.


pfemike
Professional Member

Registered: Apr 2005
Posts: 12
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 !"

dash
Professional Member

Registered: Aug 2002
Posts: 7544

quote:
--------------------------------------------------------------------------------
Originally posted by heetseeker
Dash
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]

[Irascible]

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.

[heetseeker]

Irascible
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.

[Irascible]

(Don't forget to peruse my site.)

[heetseeker]

Irascible

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.

[Irascible]

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.

[bigbird]

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.

[Irascible]

It's not nice to confuse the warehouse monkey like that bigbird. :^)

[bigbird]

The thing that got me was he was the factory rep.

[Irascible]

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.".