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D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?
2

D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

(OP)
Blast. Goofed on the house furnace/HVAC filter the other day. Regular schedule said the filter didn't need replacement, thermostat timer switch said it didn't need replacement, but it was seriously clogged anyway.
(Painting nearby? Weld fumes in the adjacent basement? Painting upstairs that clogged the fi;ter with "wet varnish" that then trapped particles? Don't know. It was solidly clogged thoguh - way before we expected to replace it. We don't smoke, no fires, no fireplace. Odd. But the filter was solidly clogged.

Sop we needed a service call, nothing else to fix the heating problem. Regardless, I could have done it myself - should have done it myself, and saved the 89.00 fee.

Installing a d/p gage across the 16 x 25 inch x 1 inch filter would be easy, but what differential pressure is expected for a house HVAC fan? Alt: A vacuum gage on the fan suction side?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

If you want to go to the trouble of installing a differential pressure gauge You can obtain a Dwyer Magnehelic new, that will suit your purpose for about $53, OR you can go on eBay and get a used one starting at about $12. Not knowing the details of your system , but typical static pressures run from 0.5" water gauge to about 3" WG on residential systems. Most gauges have movable pointers you can set for clean and dirty filters. Good luck with that.
B.E.

You are judged not by what you know, but by what you can do.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

A piece of vinyl tubing with a little oil in it will make a nice little U-tube mannometer for a few dollars.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

A service call to replace a filter? Don't you know any engineers that can help?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I love Dwyer Magnehelics. They are cheap-ish and durable, and can be used differential or single-sided by removing the right combination of plugs.

For Diesel exhausts, I use them with a range around 50 inches of water, but they are available in much lower ranges, which are not correspondingly more delicate. I'd guess 5 inches of water would be all the range you'd need for HVAC, and still have sufficient sensitivity.

For only a little more money, Dwyer offers Magnehelics with relay contacts that you can use to light an LED. You could probably power such a circuit with an AA cell or two, and not have to change the cells more often than you change smoke detector batteries.



Mike Halloran
Pembroke Pines, FL, USA

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Is there a humidifier in your system? It may need service too.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

(OP)
Yes, humidifier is present, and was on. I suspected the humidifier drain interlock was source of the problem, and had secured both power to the humidifier and water flow before calling for service. Had pumped down the water pump tank as well. Didn't work.

Suspected a bad thermostat in the 3rd stage of the house (upstairs = 1, basement = 2, upstairs back bedrooms = 3.) That didn't work either. To run the heater for a while, turning it off completely did let it turn on a run for awhile, but that was only because by turning it off manually with the power cutoff switch, I was -resetting the HVAC controller completely. So that reset the high temperature alarm condition, which let the fan and controller restart the furnace heater. After a while of heating, the clogged filter closed off too much air flow again to the fan suction, which overheated the furnace, which alarmed the controller, which promptly and correctly secured the burner.

My fault. Did everything right except suspect the real source of the problem: A clogged filter. We had replacements right next to the furnace, I just never thought of replacing them.

Blah ..........

SO, use oil in a manometer rather than water? Because it evaporates less? Is that the rationale? Cooking or a lightweight non-combustible one? If it leaks out or gets sucked into the furnace inlet, that would cause a bigger mess than a water leak, wouldn't it? (Fan suction side is heated ventilation air, not combustion air, but the two are not a perfect isolation from each other. )

If I expect a max of 3 inches water d/p, does that equate to a manometer depth (height ?) difference of 4 inches, since oil will be lighter than water?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Yes, the oil manometer will be slightly more sensitive, and less likely to evaporate. I'd make the manometer at least 15" tall, e.g. able to read to 7.5" before blowing out, and I'd put traps at both ends to catch the blowout. Dwyer sells some like that, 30" or so I think, that also roll up for storage and have valves in the ends so the liquid can be trapped for transport.

... But I'd buy a Magnehelic with relay contacts so I wouldn't have to remember to check it, and I wouldn't have to worry about the liquid evaporating or being surged out in a transient.

Mike Halloran
Pembroke Pines, FL, USA

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

(OP)
Oh, definitely. The d/p gage is more fun anyway.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I must've missed the point somewhere, is there a reason not to just set a reminder in your google calendar and change the filters every 3 months, plugged or not?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Hmm, rather than spending money on a monitoring device for what may have been a one off freak occurrence, would it maybe be better to look at this as a 'lesson learned' and add 'check filter' to any HVAC troubleshooting list?

May not stand up to DMAIC scrutiny but there you have it, until you have a history of events related to this failure mode I'd be inclined to mitigate by adding to the troubleshooting check list.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I saw a blurb in the news that fire departments recommend changing the batteries in the smoke detectors when the time changes from standard to Daylight saving and again when it changes back. I think that I will check my filters also.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Speaking of smoke detectors, we have hard-wired ones with battery backup. After about a year, they start chirping, because the backup battery needs changing. So what's the point of being hardwired?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

So what's the point of being hardwired?

The wires, Kenat, not the batts ... have wondered the same thing - why do they eat the batteries so fast?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Hard-wired smoke detectors often have another wire (14/3). If one starts alarming, then the others will join in after about 2 seconds. The same signal can also be brought out to a relay to trigger an alarm system.

The other obvious advantage of being AC powered with battery back-up is that even if you ignore the battery, they'll still work most of the time.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

(OP)

Quote (ivymike)

I must've missed the point somewhere, is there a reason not to just set a reminder in your google calendar and change the filters every 3 months, plugged or not?

We have the reminder set as a timer selection on the HVAC thermostate, but the clogged well before the alarm (3 month timer setting) was 'supposed' to off. My error - I didn't think to open, inspect and replace the dumn thing before troubleshooting.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I have been having my own furnace filter issues--furnace was short cycling and one item of interest pointed out by some googling was dirty filter. I was skeptical, but as I had another filter of the same type (Filtrete Allergen 1000) on the shelf, I did the change out. Furnace went back to normal. A month later it was short cycling again and I fixed it again with a filter change. Then two weeks later, back to short cycling. This time I put in a $2 fiberglass filter, which I figured would be less restrictive. Yesterday, I pulled it for inspection, banging it on the concrete driveway. It was loaded with fine white dust. Concurrent with the filter issue, I had brought an ultrasonic humidifier on line. I noticed white deposits under the mist nozzle, but thought nothing of this, as I have hard water. I also had noticed white dust buildup in the house I did not have before. At this point, I am thinking that the humidifier dust plugged the filter much quicker than normal. So, I shut the humidifier down. BTW, I found an HVAC industry rating system for filters--"MERV". A higher MERV number give more filtering but is more restrictive. And, it turns out Filtrete does not label their filters with the MERV number.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I would expect the hardwired detectors with battery backup to last longer between battery replacement. During operation they still draw a small amount of power to run the electronics- this is normally provided by the mains with the battery kicking in if the mains is lost. If they're not hardwired then the battery runs the electronics so it won't last as long.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

"I would expect the hardwired detectors with battery backup to last longer between battery replacement. During operation they still draw a small amount of power to run the electronics- this is normally provided by the mains with the battery kicking in if the mains is lost. If they're not hardwired then the battery runs the electronics so it won't last as long."

That's what I would expect, too. But after 1 year, they chirp until the battery is replaced. And in that year, we've lost power twice, once for 8 minutes, once for 2 minutes.

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

Hang on TenPenny, have you checked if the batteries are actually 'flat'? Or is it just a timer to change them based on safety agency recomendations e.g. http://www.usfa.fema.gov/prevention/outreach/smoke...

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

TenPenny- the smoke detectors aren't manufactured by a subsidary of Duracell are they?......

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

RE: D**m. Furnace (HVAC) Filter Overloaded, Caused on Unneeded Svc Trip. What D/P gage is needed?

I have concidered the dP just to have.
http://www.alpinehomeair.com/related/G-99.pdf

However my cheap HVAC system has a built in alarm that lets me know. about 2 seconds after the fan cuts off, I hear a "pop". the walls of the inlet duct poping back out since a high dP pulled them in

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