My latest Estimate

[robertc65]

I had another Contractor come out yesterday to give me an estimate. As I have done with the other contractors I told him my concerns are very high Heating Cost (Propane). I am not able to cool or heat the upstairs enough and that even though my Thermostat satisfies I am still feeling hot and sticky when running the AC. I mentioned that it only runs for 10 minutes at a time then shuts off. I mentioned that it does not feel like much air is being delivered from the registers (especially upstairs). I also asked if my ductwork was adequate. I have not received a formal proposal yet, but his suggestion is pretty much on par with the other estimates I have received except he also recommended the use of Scoops in my ductwork to increase the flow to my registers. He also said to damper all of the 1st floor runs. I have not heard anyone here mention duct scoops yet. Can scoops make a difference? This contractor did acknowledge that my ductwork was not large enough and said that he would never have used 5" runs or an 8" X 20" trunk at the plenum on a 4 ton system. His suggestion is to replace my current system with a new system employing a variable speed blower. He said that the variable speed blower can solve a lot of issues resulting from poorly designed ductwork. So does a variable speed blower, duct scoops and dampering 1st floor runs sound like it could help? I know I have left out a lot of detail regarding my system but, I have detailed it in previous posts and I'm guessing you guys don't want to hear me whine about it again.

Thanks Again

Rob

[pstu]

Are these scoops the same thing as turning vanes, as Dash has talked about?

Also, when you say the AC runs 10 minutes at a time, are you describing this month (May) or the peak times in summer? Because in mild weather every system is oversized. I am watching a system which is close to proper sizing and right now it has many cycles which do not exceed 12 minutes. I am expecting it to run 45-60 minutes in an hour when real summer is upon us (I know, per Manual J it should run more than 60 minutes non-stop but we will just have to see if it does).

Regards -- Pstu

[robertc65]

Are these scoops the same thing as turning vanes, as Dash has talked about?

Also, when you say the AC runs 10 minutes at a time, are you describing this month (May) or the peak times in summer? Because in mild weather every system is oversized. I am watching a system which is close to proper sizing and right now it has many cycles which do not exceed 12 minutes. I am expecting it to run 45-60 minutes in an hour when real summer is upon us (I know, per Manual J it should run more than 60 minutes non-stop but we will just have to see if it does).

Regards -- Pstu

The 10 minutes is in the Hot summer. Right now I have my windows open.

Rob

[hvaclogic]

I would have to say that your cooling is way over sized. This situation is the reason that a load calc is crucial. You're going to have to find a contractor that will take the time to do it.

[mchild]

I would have to say that your cooling is way over sized. This situation is the reason that a load calc is crucial. You're going to have to find a contractor that will take the time to do it.

Or click on the HVAC Calc tab at the top of this page, pay the $50 and do your own load calc. Then you will know that it is done with the correct assumptions like using an unrealistic 99* in the summer as compared to the stated 90*. This was done by a contractor on my home and the cooling load went from 34K to 44K (also changed the indoor temp from my desired temp of 78* to 75*- just to be safe).

[rohalon]

Sounds like your system is oversized, the duct work is probly too small for a 4 ton a/c. It might be the right size for a smaller(proper size) a/c . Dampering off the first floor will make things worse, it lowers the total airflow even more. A variable speed drive might get you a bit better cooling but with noiser airlflow to go with it. It also doesn't solve the root cause of poor cooling.

You need someone to do a load calculation, with room by room loads. Then you'll know how much airlfow needs to get to each room. Then you'll know if your ductwork need modification and what size A/C you should have.

High heating bills is probly more about insulation.

[mchild]

Are these scoops the same thing as turning vanes, as Dash has talked about?

Regards -- Pstu

No, turning vanes are used in bends to help the air flow more smoothly around the bend and reduce static pressure. Especially good on tight turns. The scoops are used at the trailing edge of the opening of a branch take off to help catch the air and send it down the take off. They increase static. Not a very good bandaid.

It sounds like the OP has an undersized duct and a VS blower will not necessarily fix the problem. It will ramp up to deliver the needed CFM, but if the resistance is too great (high static) then the motor can burn itself out trying to maintain the CFM. A VS blower is not the cure all for bad or small duct work. Unfortunately they can be "over sold" that way.

[classical]

Click here and run a load calc: http://www.heatload.com

A variable speed blower will ovecome many ductwork ills but nothing works like a properly sized and designed system especially ductwork.

A two story home needs either two systems or a zoned system.

Click here: http://arzelzoning.com/

[robertc65]

Or click on the HVAC Calc tab at the top of this page, pay the $50 and do your own load calc. Then you will know that it is done with the correct assumptions like using an unrealistic 99* in the summer as compared to the stated 90*. This was done by a contractor on my home and the cooling load went from 34K to 44K (also changed the indoor temp from my desired temp of 78* to 75*- just to be safe).

You guys keep telling me I need a load calc. I agree, but I don'tsee how relevant it is at this point. A load calc is not going to change the size of my ductwork or system. It will only confirm that the system is not designed properly. The system as designed can not deliver enough air to the registers. Doing the Manual D and Manual J calculations should be done once I find a contractor who is willing to address the root cause of my problem. It's like saying will I survive if I jump off this bridge? Uh I don't know let's measure how high it is.

[jmiles]

this is what I call a do over . start from scratch and do it right. that is the only way I would mess with it

[Sam-the-man]

You guys keep telling me I need a load calc. I agree, but I don'tsee how relevant it is at this point. A load calc is not going to change the size of my ductwork or system. It will only confirm that the system is not designed properly. The system as designed can not deliver enough air to the registers. Doing the Manual D and Manual J calculations should be done once I find a contractor who is willing to address the root cause of my problem. It's like saying will I survive if I jump off this bridge? Uh I don't know let's measure how high it is.


you need to know if your equipment is oversize or if your ducts are undersize, most likely its a combination of both. Find out what you need, then find a contractor willing to do it

[Sam-the-man]

don't bother installing a variable speed unit unless it and the ducts are properly sized, unless you enjoy expensive repairs.

[robertc65]

this is what I call a do over . start from scratch and do it right. that is the only way I would mess with it

I agree. I just have not found a contractor yet who has suggested doing so.

[dash]

You guys keep telling me I need a load calc. I agree, but I don'tsee how relevant it is at this point. A load calc is not going to change the size of my ductwork or system. It will only confirm that the system is not designed properly. The system as designed can not deliver enough air to the registers. Doing the Manual D and Manual J calculations should be done once I find a contractor who is willing to address the root cause of my problem. It's like saying will I survive if I jump off this bridge? Uh I don't know let's measure how high it is.

If your equipment is oversized ,the right sized equipment might match the duct system size better and deliver air to the farthest rooms.

[rohalon]

I think that if on yor initial call you explain your symptoms and concerns and explicitly state that you want a ran to verfiy proper sizeing, you will be able to weed out the contractors unwilling to do them without wasteing your time with setting up a sales appointment. Be willing to pay up front for both.



It's like saying will I survive if I jump off this bridge? Uh I don't know let's measure how high it is.

Maybe not the best analogy, but you are drawing the wrong conclusion. There are people that jump off bridges all the time, just about all of them survive thru good planning and careful measureing used to develope a plan to survive.