Add more returns or supplies to lower static pressure?

[Bordo11]

Using Infinity 58MVB60 air handler installed the static pressure showed by Infinity thermostat display is 0.9 – 1.0. It seems a bit high.
The air duct (supplies) sizes I have calculated for the 600 – 700 CFM by using well know HVAC Calc software tool.

I removed the air filter insert from an air purifier GAPA body, keeping the filter compartment open letting easier for the air to get into the air handler.
I was surprised that the static pressure went up by 0.1

It is an old house and the ducts installation was a real pain.
But I want to get the pressure down to appropriate 0.5 level or so.

My question is should I add more returns or more supplies?

[beenthere]

To know that. You ned to know if its the supply or the return or both that are causing the high static.

[udarrell]

I wouldn't trust those figures. If those figures are correct the situation must be dealt with.

Get & use an instrument you can trust to check static pressure.
Do some SP testing to find exactly where the problem areas are.

If you can measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area) - Darrell

[Bordo11]

Thanks for your suggestions.
I wanted to make it simpler, just making an empirical assumption.
If the system would lack returns by opening an air filter compartment and creating additional virtual return the static pressure should drop. But instead it went up.

Should not be enough just to assume:
A. If by adding a supply pressure drops, it means add more supplies.
B. If by adding more returns pressure drops, it means add more returns, but again, in this case pressure went up.
What is wrong?

[perrybucsdad]

I wouldn't trust those figures. If those figures are correct the situation must be dealt with.

Get & use an instrument you can trust to check static pressure.
Do some SP testing to find exactly where the problem areas are.

If you can measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area) - Darrell

I did just that this weekend. I picked up a device from Grainer last friday to check the SP with various different configurations. I was able to find it after the filter, but it didn't even register anything after the coils. I must be doing something wrong. What I wanted to do was to see what the SP was at various different ducts in the basement, but it didn't even register on the testing device.

[beenthere]

.

If your supply static rises when you add return, your supply duct is also restricted.

[beenthere]

I did just that this weekend. I picked up a device from Grainer last friday to check the SP with various different configurations. I was able to find it after the filter, but it didn't even register anything after the coils. I must be doing something wrong. What I wanted to do was to see what the SP was at various different ducts in the basement, but it didn't even register on the testing device.

What gauge/meter are you using. What kind of probes.

[perrybucsdad]

What gauge/meter are you using. What kind of probes.

Dwyer U Inclined http://www.grainger.com/Grainger/items/3T294. As far as the probes... That may be part of the problem. I'm not exactly sure how they are to attach. My first though was that you just slip it over the tube, but the fit is just too tight. I then noticed those red long "thingys" (sorry for the technical term). That is what I eventually used to connect it, but which end goes in the tube and which end goes in the hose, as it kept collapsing (folding over) on itself. I didn't want to ask here because of the no DIY rule, so I will more than likely just sell it since I can't seem to figure out how you use the darn thing and Dwyer has yet to answer my email.

[beenthere]

Those long red thingys are what you put in the u tube.

Thats not a good gauge for static testing, because its hard to see a .02 movement with it.

Systems with very restrive returns, won't get much static pressure on the supply side of the evap coil of furnaces.

[perrybucsdad]

Those long red thingys are what you put in the u tube.

Thats not a good gauge for static testing, because its hard to see a .02 movement with it.

Systems with very restrive returns, won't get much static pressure on the supply side of the evap coil of furnaces.

Now you tell me. Okay, so what would be a better gauge to measure with, without spending a ton of bucks.

[beenthere]

Inclined manometer. Or a Magnahelic gauge that reads pos and neg presure in tenth of inches.

An arm and a leg to you, maybe a sprainge to me. Or vise versa.

[perrybucsdad]

So something like the Dwyer Mark II Model 25 Incline Manometer. That was the one I wanted originally, but they didn't have it in stock. I also think there is the Binford 9000 with Flux Capacitor, leaf blower, and swiss army knife too.

Anyone want a slightly used Dwyer?

[beenthere]

So something like the Dwyer Mark II Model 25 Incline Manometer. That was the one I wanted originally, but they didn't have it in stock. I also think there is the Binford 9000 with Flux Capacitor, leaf blower, and swiss army knife too.

Anyone want a slightly used Dwyer?

You forgot the high powered band aid dispenser the Binford comes with.


Donate it to your local tech school/college.

[firecontrol]

Using Infinity 58MVB60 air handler installed the static pressure showed by Infinity thermostat display is 0.9 – 1.0. It seems a bit high.
The air duct (supplies) sizes I have calculated for the 600 – 700 CFM by using well know HVAC Calc software tool.

I removed the air filter insert from an air purifier GAPA body, keeping the filter compartment open letting easier for the air to get into the air handler.
I was surprised that the static pressure went up by 0.1

It is an old house and the ducts installation was a real pain.
But I want to get the pressure down to appropriate 0.5 level or so.

My question is should I add more returns or more supplies?

Are we to assume that you installed this system yourself?

If you didn't, then you should be calling the installing contractor back if you have concerns about the TSP the control is showing.

Either way you've just found out first hand one of the first basic rules of air flow in ductwork. Velocity increases static pressure.

[perrybucsdad]

Donate it to your local tech school/college.

Great idea!!

Either way you've just found out first hand one of the first basic rules of air flow in ductwork. Velocity increases static pressure.

and so we should also conclude that dead animals in the duct work can decrease static pressure?

[perrybucsdad]

If your supply static rises when you add return, your supply duct is also restricted.

So what does this mean if you add more return but your supply side does not get effected at all? Still some sort of blockage in the supply side (like a dead animal )?

[beenthere]

If its a VS blower. They don't always increase when you decrease the return.

[perrybucsdad]

If its a VS blower. They don't always increase when you decrease the return.

, I didn't decrease the return, I increased it (or are you talking about the pressure?) When I say I increased it, I mean I added more air to it by opening the blower door.

Also, when you say VS blower, do you mean a blower that a tech can jumper to adjust the blower speed or something that is controlled through some sort of circuitry that will increase or decrease the speed. In my case, the blower has to be jumpered (or whatever you guys call it).

Personally, I think there is something in the supply side either before or after the cooling coil. I have a call into a different servicing company that will do the annual maint on the unit. My Dad really recommended them as he has used them numerous times for when he builds his YMCA Dream homes. I'm thinking something is up there and hopefully they can fix that when they do their maint. Either that or the cockamamie way they have all the supply lines coming off the main trunk right after it leaves the furnace is the problem. Either way, I'm not sure how much that will cost, but it should pay for itself with added comfort and hopefully reduced bills.

[beenthere]

I was talking pressure.

VS blower are adjusted by jumpers/dip switches.

[firecontrol]

and so we should also conclude that dead animals in the duct work can decrease static pressure?

No...... dead ones would increase static pressure along with increasing a few other things in the home but let's not go there.