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Old 04-20-2009, 11:35 AM   #76
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Excellent. Thanks!

This all makes sense. I will look into doing the load calculation, although given that the system is already installed, there isn't much I can do to change things now. I have heard that a fair estimate is between .8 and 1.5 CFM's per sq. ft. Is that even remotely accurate?

As for the return, I think there are photos on page 4 of this thread. Effectively all I have a a straight drop into an ell. Based on the photo, do you think I can go right from the return air drop to the supply plenum?

Thanks for the suggestion of the honeywell unit. It looks great! I'd just need to add the bypass damper and the regular dampers, right?

I will probably add a humidifier in at the same time. Do you have any thoughts on whole house dehumidifiers as well? DC has horrible humidity!

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Old 04-20-2009, 11:42 AM   #77
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Each floor will need a different amount of air flow.

Those rules of thumb are good for causing trouble.

The basement will need less then the third floor.
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Old 04-20-2009, 11:44 AM   #78
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Makes sense. I will run the calculation. I wish I was installing the system from scratch, but what can you do, right?

Also, if I need to move the unit and the AC lines don't have any give, how hard is it for a pro to extend them? Is it even possible?
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Old 04-20-2009, 07:45 PM   #79
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Its not hard to extend the lines.
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Old 04-20-2009, 07:50 PM   #80
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Good news. Is extending the lines DIYable? Or best left to a pro?
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Old 04-20-2009, 08:15 PM   #81
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Need a tech to pump down, vacuum, and recharge, or check charge.
Pkus to braze them if you don't have a tourch set up.
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Old 03-09-2010, 09:16 PM   #82
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I am sorry to revive this old thread, but I thought it made sense to do so as my questions are really just a continuation of the issues raised previously. Hopefully this makes things easier and less confusing.

Short story is that with the help of some of the forum members here, especially beenthere, I learned that the ductwork in my house was poorly designed. We will be adding a small addition over the course of the next few months and I'd like to at least start to address some of these issues. The air handler/furnace as well as the ac coil/condenser were both installed just two years ago, right before we purchased the home and while they're not the best and are a little oversized for the home, but we plan on sticking with them. The details for the equipment can be found here.

Right now I just have some basic duct design questions, but I am sure more specific ones are not too far away.

1) I downloaded the demo for HVAC Calc and have been entering the specifics for my house. If anyone has any experience with this software, how do you handle and open floor plan? Our kitchen and dining room are only divided by a half wall. Should I treat this as just one room?

2) I have heard that HVAC Calc does not do a great job with duct design. Given that I do not need help choosing my equipment, but only with duct design, is HVAC Calc even going to be helpful? Is it worth purchasing the two month license? I am guess that the heat loss/gain info it will give me will help to make the right decisions, right?

3) I know that there are some best practices for duct design/placement, like installing supply registers in the ceiling on exterior walls, usually above windows and doors. Are these registers meant to "wash" the wall or blow air into the room? Given that I am retrofitting a 75 year old brick rowhouse, these locations aren't always possible. How big of a deal/problem is this? Such as ducts being located in the floor along interior walls?

4) Our basement is finished (and my mother-in-law lives there), so it is important that it be as comfortable as the rest of the house. How effective is it to install a circular register in the center of the ceiling? Assuming it is properly sized, is this effective?

5) As this thread determined, our return is significantly undersized. Currently we just have a return air drop into an ell through a filter and into the side of the air handler. There are photos here. Our furnace room is tight on space and I am wondering if there is a more efficient setup that might gain me some extra space to allow me to up the size of the return air drop. For example, I have seen right angle return air shoe or this support box with filter or any of the options found here. Do these options use less space than a standard cold air shoe/ell?

Any thoughts or advice would be very much appreciated!!
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Old 03-10-2010, 04:55 AM   #83
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Quote:
Originally Posted by stubits View Post

1) I downloaded the demo for HVAC Calc and have been entering the specifics for my house. If anyone has any experience with this software, how do you handle and open floor plan? Our kitchen and dining room are only divided by a half wall. Should I treat this as just one room?

Yes, list it as one room, since the air can travel relatively freely between the 2.

2) I have heard that HVAC Calc does not do a great job with duct design. Given that I do not need help choosing my equipment, but only with duct design, is HVAC Calc even going to be helpful? Is it worth purchasing the two month license? I am guess that the heat loss/gain info it will give me will help to make the right decisions, right?

It isn't good for designing the actual physical size of the duct. But it is good for finding out how many CFM's an area needs. And then using standard methods to determine duct size from there.

3) I know that there are some best practices for duct design/placement, like installing supply registers in the ceiling on exterior walls, usually above windows and doors. Are these registers meant to "wash" the wall or blow air into the room? Given that I am retrofitting a 75 year old brick rowhouse, these locations aren't always possible. How big of a deal/problem is this? Such as ducts being located in the floor along interior walls?

A register in the ceiling for heat, should throw the air down. It should have a spread that washes an area of the wall also.

A floor supply on an inside wall, won't get you as much comfort as if it was on an outside wall. But as long as it has good through to miz teh 2 airs. it will heat or cool the room.

4) Our basement is finished (and my mother-in-law lives there), so it is important that it be as comfortable as the rest of the house. How effective is it to install a circular register in the center of the ceiling? Assuming it is properly sized, is this effective?

Round ceiling registers are great for cooling, not so good for heating.

Anyway to position it off center so its toward an outside wall, and then install a rectangular one instead.

5) As this thread determined, our return is significantly undersized. Currently we just have a return air drop into an ell through a filter and into the side of the air handler. There are photos here. Our furnace room is tight on space and I am wondering if there is a more efficient setup that might gain me some extra space to allow me to up the size of the return air drop. For example, I have seen right angle return air shoe or this support box with filter or any of the options found here. Do these options use less space than a standard cold air shoe/ell?

Any thoughts or advice would be very much appreciated!!
The "support" type you linked to. Are very very restrictive to air flow(I'd have to censor myself if I told you what I think of them).
The right angle is better.
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Old 03-10-2010, 08:54 AM   #84
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Jim-

Thanks so much, this is tremendously helpful. I will go ahead and purchase the two month license of HVAC Calc and start to figure out the ductwork from there.

When you say determining duct sizes using "standard methods," do you mean using a ductolator or some of the rules of thumb, like a 6" round supply line puts out about 110 cfm? Can you point me in the right direction for the standard methods? I have read some interesting material here and even better here. Do either of those resources look good/usable?

I am located in DC and my experience is that we have equal parts heating and cooling demands (although the heat loss/gain calculations will tell the truth, right?). We have cold dry winters, 30's and below for about 3-4 months and hot, very humid(90%) summers, 90's and above for about 3-4 months. Our supply registers on the upper level are in the ceiling on outside walls and I think these are sized more or less correectly. On the home's main level, the registers are all in the floor and are located wherever they could be placed conveniently, but not on exterior walls. We are in a rowhouse though, so we only have 2 exterior walls, the other 2 outer walls are shared with our neighbors. Based on "rule of thumb" the vents seem to be properly sized, if not perfectly located. The problem however is that while the ductwork for the main level is sized perhaps close to correctly, the previous owners simply tapped into it to supply the finished basement, effectively cutting it in half. I guess I will have a better idea of what is going on after I get the data from HVAC Calc, but any thoughts or impressions?

I am hoping to be able to keep the ductwork for the upper level with minor modifications and am hoping that the ductwork for the main level will be workable if I close off the vents to the basement, but that means I will need to add new runs for the basement. Thanks for the info regarding the round registers, I will be sure to use the rectangular. What is the best place for the register in a room that does not have any exterior walls at all? Does placement mattter in that case?

Does the right angle return take up less space than the standard cold air shoe/ell with a filter frame? I am guess it is a better option, but what has your experience been? I will definitely avoid the support box. Thanks!

Thanks!
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Old 03-10-2010, 10:48 AM   #85
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The right angle box and a return ell will take up just about the same amount of space, if the ell is made for a 4" air filter.

That PDF uses some real bad rules of thumb.

Udarrels guide line are based a bit on rules of thumb. So if you use it. You end up with having to put in ALL new duct work.

This is where a manometer, and or vane anometer would help a lot.
They would allow you to determine existing CFM to each room, and to measure current static pressure. And from there determine what course of action to take.

Lacking those.

Figure. You are NOT getting more then if even 100CFM through a 6" sheet metal supply(undersized trunk line prevents it).

A larger trunk line will help reduce static loss before the supply runs, and increase the amount of air from all of your supplies.

Can you draw and post a diagram of your duct work. And give lengths and sizes of it.
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Old 03-10-2010, 11:30 AM   #86
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As always, thanks so much. Really helpful. So, I will stay away from the PDFs for fear that they are just going to cause more trouble than they are worth.

If buying a manometer/vane anometer would make this easier and better, I am happy to do so. Which is preferred, any recommendations? Since I'll only be using it this one time, I'd like to go with the bare minimum necessary to get the data I need. Any thoughts? This looks pretty cheap, but would it work? Or how about this? Or am I cheaping out too much and need something with more features like this?

I will draw up a diagram of my ductwork tonight, its not too complicated, so it shouldn't be all together difficult. As a preview, I have three trunks connected into the supply plenum, two 8x10s, each serving half of the basement and half of the main floor - (4) 6" ducts + (1) 4" duct on one and (4) 6" ducts on the other, each 8x10 extends about 20' from the furnace - and a 12x10 that runs ~ 20' straight up to the attic where tees off into two 8x8 each servicing half of the upper level - (1) 6" duct + (2) 4" ducts on one and (2) 6" ducts on the other, each 8x8 extends about where it tees off, or a total of about 40' from the furnace.

I am willing to do pretty much whatever is necessary with the ductwork to get this to work right, but as I said, I am pretty much stuck with the equipment. I am curious to see, after I finish with HVAC Calc just how oversized my system really is. The house is three finished floors, each about 625 sq. ft, or about 1,875 sq. ft total, with limited insulation in the attic (r-14) and no insulation in the exterior walls (double wythe brick with plaster applied directly on top). I am hopeful I can reuse as much as possible of the existing ductwork, and especially the holes already cut for the registers in my hardwood floors!

I need to figure out return air as well, but I think our previous conversations helped a lot, I just need to figure out how to fit it all in my small furnace room!!

Thanks!

Last edited by stubits; 03-10-2010 at 05:53 PM.
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Old 03-10-2010, 06:59 PM   #87
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The first one doesn't seem to display FPM.

Both of the other 2 do. So either of the those 2 will work.

Using them will allow you to figure out the CFM being delivered to each room.

Don't really need to get the most expensive.
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Old 03-10-2010, 10:11 PM   #88
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Excellent, I will order the lesser expensive of the two ASAP.

I know that my return air is WAY undersized, which means current CFMs of supply is also low, so testing it will only show so much. If I open the blower door while the system is running, should that compensate for the undersized return?

Does it make sense to figure out the ductwork in a "perfect world" and then figure out how to make that work with what I've got?

What is the best place for the register in a room that does not have any exterior walls at all? Does placement mattter in that case? This is related to one of the rooms in our basement.

Any thoughts on the current supply ductwork I described in a previous post? What does your gut say?

Thanks!!
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Old 03-11-2010, 01:55 AM   #89
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You want to check supply and return CFM with the blower door on. This will show you if your return has more air leakage then the supply.
You'd be surprised how many homes have 10 to 20% more supply air then return. Which means its pulling in air from some place other then the conditioned areas.

Generally works best to do the duct design for ideal standards. Then see what can really be done.

If a room has no outside walls. Placement of a register is based on where its both convenient, and will not be blocked by furniture, or interfere with people.

Gut feeling on the supply duct? Um, shouldn't have to redo all of it.
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Old 03-11-2010, 04:13 PM   #90
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Awesome. Thanks so much!

So, I guess the next step in this process is to finish entering my info into HVAC Calc and get the heat loss/gain calculations, right?

Once I have that, how do I go about designing the ducts for ideal standards? Are there any good resources you can point me to? Is this ductolator a good resource?

Once I get the anemometer, what should I do with it? Obviously I want to measure the fpm coming out of/into each register, both supply and return, but any method to the madness? Should I open each register completely? Right now I have some of them dampered a bit to improve air flow throughout the house. Or leave it as is?

I would like to add zones to the system, either 3 or 4, but the duct design I am considering will accommodate it well, I think, but I have a couple of questions. 1) Does zoning change the duct design much, as in the sizing? 2) In an attempt to spread out costs, can I install the dampers as I upgrade the ductwork, run the wires, but not install control panel? 3) How does one go about sizing the bypass damper? 4) Is this guide any good?

We would also like to add a humidifier, is there a particular type that you like best? Steam? By Pass? Flow Through?

This whole thread started because of major problems with my return air and I want to make sure to correct that as well. I have a couple of questions to start out with: 1)Are return registers better located in the ceiling, the upper part of the wall or close to the floor? Does it depend on each floor? In the basement and in the main level it will work out so that there is just one return on each level, but can install them in any location, high, low or in the ceiling, what's the best option? On the upper level, I will install returns in each bedroom, but can only really install them in the ceilings, 2) they should be on interior walls, right? In the basement, I want to be careful not to pull air that is necessary for combustion for the water heater and the furnace. The basement has 3 rooms, a bathroom, a living room (where the utility closet is located) and a bedroom. There are doors between each of these rooms, but the bottoms are cut to allow airflow. I would like to install the return in the bedroom, is this a bad idea? Is it possible to use outside air for combustion? If so, how?

Thank you so much all the time you've taken to answer my questions. I have no idea where I'd be without you. I am excited to embark on this project and excited for the outcome... a more comfortable home!!!

Thanks!!

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