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Started By
Message
My HVAC has a static pressure of 1.69....
Posted on 6/28/23 at 6:07 pm
Posted on 6/28/23 at 6:07 pm
How bad is this and what can I do to lower it? System is about a 4 year old 5 ton with 2 speed fan.
2
Posted on 6/28/23 at 10:14 pm to mikie421
Yikes - was that measured by a HVAC tech? You certain on the accuracy of that number? In human terms that would be like having a blood pressure of 220 over 120 - not good a all.
If the value is correct, potentially a vastly oversized tonnage with considerably undersized ducts - supply ducts, return ducts or both. How large is your house - square footage. Was a much larger unit (tonnage) placed retaining duct work for a much smaller system?
I assume 1.69 is total external static pressure (TESP) - you would need both the return and supply static pressures to see if the main problem is in the return side or supply side of the system, or both.
You also need to know what static pressure rating for your furnace or air handler is - that info should be in the furnace/air handler owners manual, or online for your model number.
Many system are designed for max air flow in CFM at a static pressure of 0.5 in WC (inches water column) TESP, mine is, some are 0.8 in WC, others as low as 0.2 in WC - depends on the manufacturer.
Curious - knowing HVAC static pressure is a good thing, but it’s seldom measured by techs - what induced you or someone to measure it? You having problems?
If the value is correct, potentially a vastly oversized tonnage with considerably undersized ducts - supply ducts, return ducts or both. How large is your house - square footage. Was a much larger unit (tonnage) placed retaining duct work for a much smaller system?
I assume 1.69 is total external static pressure (TESP) - you would need both the return and supply static pressures to see if the main problem is in the return side or supply side of the system, or both.
You also need to know what static pressure rating for your furnace or air handler is - that info should be in the furnace/air handler owners manual, or online for your model number.
Many system are designed for max air flow in CFM at a static pressure of 0.5 in WC (inches water column) TESP, mine is, some are 0.8 in WC, others as low as 0.2 in WC - depends on the manufacturer.
Curious - knowing HVAC static pressure is a good thing, but it’s seldom measured by techs - what induced you or someone to measure it? You having problems?
This post was edited on 6/28/23 at 10:48 pm
Posted on 6/29/23 at 9:38 am to CrawDude
The pressure number is coming from my thermostat. House is 2200 sq ft with 12 and 10 ft ceilings. This did replace a 4 ton unit that was running 24/7 in the summer.
I know its hot out there, in the afternoon it can only get down to about 74.
I know its hot out there, in the afternoon it can only get down to about 74.
Posted on 6/29/23 at 12:36 pm to mikie421
Is it a communicating system? Hard to believe a t-stat can give you that without being communicating.
Assuming it is communicating, you need to start by lowering CFMs as much as you safely can (like 350cfm/ton) and be sure to choose an appropriate air filter with the lowest drop you can find for your filter size.
Make sure none of your return vents are covered and all your supply vents are open.
Assuming it is communicating, you need to start by lowering CFMs as much as you safely can (like 350cfm/ton) and be sure to choose an appropriate air filter with the lowest drop you can find for your filter size.
Make sure none of your return vents are covered and all your supply vents are open.
Posted on 6/29/23 at 12:38 pm to mikie421
quote:
This did replace a 4 ton unit that was running 24/7 in the summer.
So....your 4ton was probably the correct size. Going to 5ton was probably not a good move. Your ducts will likely be undersized for 5 tons creating high pressures. If your system is communicating with a variable speed ECM fan, this will definitely shorten the life of the fan motor, too.
You want a cooling system to run non-stop during peak heat times (95F+ from 2pm-7pm type of thing).
When you say it can only get down to 74F, are you talking about the new system or old?
Posted on 6/29/23 at 1:34 pm to notsince98
new system can only get down to 74 when its 95+ outside.
I do have some ducts in the attic dampened, I can go up and open them all the way....was trying to force more air into certain rooms.
I do have some ducts in the attic dampened, I can go up and open them all the way....was trying to force more air into certain rooms.
Posted on 6/29/23 at 1:45 pm to mikie421
I'm not a HVAC expert but a 5 ton unit for a 2200 sqft house seems way big
This post was edited on 6/29/23 at 1:46 pm
Posted on 6/29/23 at 2:23 pm to mikie421
Notsince98 has provided good answers/suggestions. But the bottom line is if a 5 ton unit was placed on a duct system designed for 4 ton unit, your system is still only providing 4 tons of cooling capacity at a much higher energy cost and over time it will reduce the life of system at a static pressure that high.
In the short term I’d suggest what Notsince98 recommended to lower your blower speed to 350 cfm per ton from the likely factory setting of 400 cfm per ton. That should help reduce static pressure and increase air flow somewhat.
However, I would also arrange to have a direct static pressure measurement with a manometer - takes all of 5 minutes for a tech to do. I would not assume the calculated static pressure from the algorithm is accurate - it may be but I’ve also read where they can be notoriously inaccurate.
This is not an emergency issue, but I’d have it done - you need to know if the duct work, both return and supply, is now the issue - that can be fixed. Tech could also lower your blower speed if you’re not comfortable with doing this yourself. Another tip - if you go forward with this, you want to request a senior tech - one familiar with measuring static pressure and has good knowledge of duct work.
Open the dampers until you can get your static pressure issue resolved, then you can rebalance air flow to rooms if need be.
In the short term I’d suggest what Notsince98 recommended to lower your blower speed to 350 cfm per ton from the likely factory setting of 400 cfm per ton. That should help reduce static pressure and increase air flow somewhat.
However, I would also arrange to have a direct static pressure measurement with a manometer - takes all of 5 minutes for a tech to do. I would not assume the calculated static pressure from the algorithm is accurate - it may be but I’ve also read where they can be notoriously inaccurate.
This is not an emergency issue, but I’d have it done - you need to know if the duct work, both return and supply, is now the issue - that can be fixed. Tech could also lower your blower speed if you’re not comfortable with doing this yourself. Another tip - if you go forward with this, you want to request a senior tech - one familiar with measuring static pressure and has good knowledge of duct work.
quote:
I do have some ducts in the attic dampened, I can go up and open them all the way....was trying to force more air into certain rooms.
Open the dampers until you can get your static pressure issue resolved, then you can rebalance air flow to rooms if need be.
Posted on 6/29/23 at 3:15 pm to CrawDude
Thanks for the replies!
Posted on 6/29/23 at 3:36 pm to mikie421
Where's your HVAC unit located? Adding ducts/ vents is never cheap, but a fairly easy solution to this would be to add a duct or some vents especially very close to your unit. Basically allow it to release pressure.
But if you now have an oversized unit basically AND you are having issues cooling certain areas of your home then IMO (and I'm not a HVAC tech) your solution should be to strongly consider adding ducts/ vents to your areas that need them AND open up the other areas.
I'm not sure how variable units work, but I would imagine they are still adjustable. Most units come with the highest fan speed setting from the factory as that is the most energy efficient. The unit needs to run less. But you may be better off turning your fan speed down as said and having it run more.
But if you now have an oversized unit basically AND you are having issues cooling certain areas of your home then IMO (and I'm not a HVAC tech) your solution should be to strongly consider adding ducts/ vents to your areas that need them AND open up the other areas.
I'm not sure how variable units work, but I would imagine they are still adjustable. Most units come with the highest fan speed setting from the factory as that is the most energy efficient. The unit needs to run less. But you may be better off turning your fan speed down as said and having it run more.
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