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Cost of duct work
Old 02-11-2014, 02:24 PM   #1
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Cost of duct work

OK... I know there has been enough discussion on here to know there are some knowledgeable guys and gals that might be able to help me out..

We have a problem with the temp diff between upstairs and downstairs... it is worse this year. At least 5 degrees...


So, I was looking at getting a zoned system with dampers. One guy came out and said that our duct work is pretty old and it would be better to get it replaced... they also said that there is too many runs off our 'box' (can't remember the actual term right now)...

Has anybody had their duct work replaced and can you give me an estimate of how much it cost... with sq. ft. of house? Just looking for a ballpark figure....

My first quote was $5,250 and we have 2,700 ft...


BTW, the duct work does seem to be all over the place and I know for sure that we are not getting the air flow we need for downstairs...
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Old 02-11-2014, 02:37 PM   #2
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Can't answer the question re:cost of new ducting, but I had experience with my new construction house in Texas where the builder used a zoned (upstairs/downstairs) system with dampers controlled by thermostats and a key part of making this all work well, and it did, was that he increased the size of the return in the upstairs so that more of the cool air (in summer) was pulled upstairs and in the winter it returned more of the heated air downstairs. This saved me on electricity since I only had one unit running versus two and an appropriately loaded system is always more efficient than one or two underloaded systems.

The decision to invest in new ducts (for me) would revolve around the number of years I was going to be in the house and whether family members had allergies that may benefit from new ductwork. Not sure there is much resale on disclosing new ductwork on a sale.

Good luck.
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Old 02-11-2014, 02:44 PM   #3
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A couple of questions occur is the ducting sheet metal or plastic pipes? (That can make a big difference) Second do the ducts run in areas where there is no attic? I had plastic pipe ducts replaced in a house in Houston of 1800 sq foot where the pipes all ran thru the attic, and it cost about 2k (don't remember actual cost because I also had more insulation added as it had settled over 20 years).
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Old 02-11-2014, 02:46 PM   #4
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TP,
Some questions:
- If you run the fan all the time (set it to "on" instead of "auto") do you still have the disagreeable temperature differences?
- Is it hot upstairs and cold downstairs now (i.e. in the heating season)?
- Is the temperature difference always 5 degrees, or is it closer to equal just after the heater cycles "off"?
- How old is your house, how "tight" do you think it is, and how well insulated?

Obviously, the ductwork just delivers the hot (or cold) air when the system is running. Many multi-story houses have issues with temperature stratification (hot air rises--to fight that requires active measures) and differential heat loss from various parts of the house (i.e. cold corner rooms, cold "bump-out" rooms, etc)
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Old 02-11-2014, 02:49 PM   #5
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Originally Posted by Texas Proud View Post


BTW, the duct work does seem to be all over the place and I know for sure that we are not getting the air flow we need for downstairs...
Hey,

Do you have more than one return for the air to get back to the "box"?

If you only have one return and it is on the 2nd floor you would not get enough air to the first floor.

I had this issue with a single floor house 2000 sq feet with only one return far from the master bedroom and bath. If the bedroom door was left open about 6 inches, it would slam shut whenever the AC came on. Adding a return in the master bedroom solved the problem.

Close your doors on the first floor while the AC is running and put your hand on the floor in front of the crack at the bottom. If you feel air rushing out from under the door you aren't getting enough air returning from the first floor to the AC unit.

Adding a return to the first floor can be difficult but can be done. If this is the issue find another AC company.

Se ya

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Old 02-11-2014, 03:49 PM   #6
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If you have dampers already installed near the take-off points of the branch ducts [usu. 4 - 6" diameter] you can try to determine what branch goes to what room. Then favor the cool room by opening it's damper 100%, and closing the hot rooms down a little. Floor registers also may have dampers.
There are also inline booster fans that can be added to colder ducts if you have room to do it.

I have no idea about cost, but make sure you consider the cost of any wall restoration that may end up needing to be done. Sometimes that is pricey, too.
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Old 02-11-2014, 03:50 PM   #7
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OK, great questions and I will try and answer them all...

I am not looking to get a second system at this point... just use the one.

They say I do not have enough return air, and I have a very small return downstairs.... they said they would look into possible making it bigger. The did suggest that we add small 12x12 returns in all the upstairs bedrooms (total of 3).

We do have runs that go between floors. It is an old aluminum faced flex duct.. there does appear to be some of the grey plastic. I can see where they did not make great connections, only using duct tape at a few places.

If you turn on the fan, it does not even out the temp problem. We have the problem at all times, even when the heater is going, the upstairs is warmer than downstairs....

Now, during the summer when it is AC time... the upstairs get more sun and heats up faster, so it is warmer then...

House was built in the 80s... but it is pretty tight. We have a good layer of blown in over the batt... I have low electricity bills, so I do not think that is a problem.


I am asking that they look into putting more return air on the first floor... will have to see if that is possible without a lot of tear up...


Thanks for the questions...
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Old 02-11-2014, 03:52 PM   #8
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If you have dampers already installed near the take-off points of the branch ducts [usu. 4 - 6" diameter] you can try to determine what branch goes to what room. Then favor the cool room by opening it's damper 100%, and closing the hot rooms down a little. Floor registers also may have dampers.
There are also inline booster fans that can be added to colder ducts if you have room to do it.

I have no idea about cost, but make sure you consider the cost of any wall restoration that may end up needing to be done. Sometimes that is pricey, too.
We do not have any dampers in the ducts... we have adjusted the outlets in the rooms to try and help as much as we can... still have airflow problems...


At this time, we are only looking at replacing and upgrading what can be done without tearing up walls... I do not want to go to that level....
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Old 02-11-2014, 04:25 PM   #9
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OK, great questions and I will try and answer them all...

I am not looking to get a second system at this point... just use the one.

They say I do not have enough return air, and I have a very small return downstairs.... they said they would look into possible making it bigger. The did suggest that we add small 12x12 returns in all the upstairs bedrooms (total of 3). ...
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Originally Posted by Texas Proud View Post
We do not have any dampers in the ducts... we have adjusted the outlets in the rooms to try and help as much as we can... still have airflow problems...


At this time, we are only looking at replacing and upgrading what can be done without tearing up walls... I do not want to go to that level....
I agree that it probably makes sense to try some simple things first - it might get it to 'good enough' for you. A couple things that are not clear to me (sorry if I missed them):

So, just what air returns do you have upstairs now? You said they want to add some upstairs (which seems reasonable, but me$$y as you say).

No dampers at all? Are you sure? We have them in most runs (metal pipe though), they are not obvious, just a little wing nut sticking out to lock an internal butterfly plate in place. [edit - I missed the 'adjusted outlets' comment - ignore this line: And most of our heat vents (supply) in the rooms have a louvered thing with a little handle that you slide to open/close. Those are usually just drop in replacements available at any big-box HW store. ]

You could just cover the upstairs supply vents temporarily to see if it helps. The one issue you may run into - if you block off the entire upstairs, that might not allow enough airflow through the furnace (make sure everything is fully open downstairs), and your furnace will shut down due to over temperature, and then restart when it cools - but that's not ideal. Adding more supply downstairs may help for both issues.

They also make booster fans that go in the duct lines - possibly a few of these in the downstairs ducts will help get more air flow down there. You'll have the opposite problem in summer months (or is that 'non-winter months' in Texas?).

-ERD50
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Old 02-11-2014, 04:29 PM   #10
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We do not have any dampers in the ducts... we have adjusted the outlets in the rooms to try and help as much as we can... still have airflow problems...

...
Sorry, I missed the 'adjusted the outlets' comment.

So you have every supply in the upstairs rooms closed, no hot air being delivered up there at all, and it is still 5F warmer than downstairs?

If everything is open downstairs, then I think you really must have an air return problem from the upstairs. Hmm, or maybe even the downstairs - if those downstairs air returns are not pulling in the air delivered downstairs, then the upstairs returns are pulling hot air up, hmmmm, but it seems it would have cooled down by then.

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Old 02-11-2014, 05:48 PM   #11
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Sorry, I missed the 'adjusted the outlets' comment.

So you have every supply in the upstairs rooms closed, no hot air being delivered up there at all, and it is still 5F warmer than downstairs?

If everything is open downstairs, then I think you really must have an air return problem from the upstairs. Hmm, or maybe even the downstairs - if those downstairs air returns are not pulling in the air delivered downstairs, then the upstairs returns are pulling hot air up, hmmmm, but it seems it would have cooled down by then.

-ERD50
Responding to both of your posts....

No, we do not have all outlets closed upstairs... we have about half of them closed...

No dampers at all... we have flex ducts... that is why I am thinking about automatic dampers with multiple thermostats...

Are you calling supply vents the return air If so, we have a 20X25 at the top of the stairs and a 12X20 downstairs in the ceiling... the furnace is sucking the air filters strongly.... the guy even said he had not seen one being pulled like this... that is why they are suggesting either one larger return in our game room or three smaller ones in the bedrooms... This only helps on the upstairs... we will have to see what they can do for downstairs...


I just checked and the temp difference is 7 degrees.... so it is worse than I thought it was...
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Old 02-11-2014, 05:58 PM   #12
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I was reading and found one article that said about $200 to $300 per vent... SO I went and counted the vents that we have... 21!!!

So, the quote seems to be in the middle...

Plus, they are going to fix the return and add additional...
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Old 02-11-2014, 06:53 PM   #13
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I've had problems with temp stratification in the 2 story houses I have had. Just turned the fan on and left it on 24 hrs a day 365 days a year. Never had a problem with the stratification with the fan always running. Never had a problem with burning out a fan either. You do have to change the filters more often.
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Old 02-11-2014, 07:02 PM   #14
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In an ideal world, you'd have 2 systems, one for upstairs and one for down.
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Old 02-11-2014, 07:57 PM   #15
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We do not have any dampers in the ducts... we have adjusted the outlets in the rooms to try and help as much as we can... still have airflow problems...


At this time, we are only looking at replacing and upgrading what can be done without tearing up walls... I do not want to go to that level....
Just to confirm look at the box the flex ducts come from. In my house in Houston there were dampers at the point where the box transitioned to the flex duct.
One other thing following what is done by Mike Holmes, see if the heating guy has an cubic foot per minute meter, and measure the airflow at the outlets. That will give some better indication of flow restrictions. If you can find the manual on the furnace or air handler it should tell you what the potential capacity of the blower in CFM is. If the total measured is less then its possible there could be an undetected duct leak.
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Old 02-11-2014, 09:00 PM   #16
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Responding to both of your posts....

No, we do not have all outlets closed upstairs... we have about half of them closed...

No dampers at all... we have flex ducts... that is why I am thinking about automatic dampers with multiple thermostats...

Are you calling supply vents the return air If so, we have a 20X25 at the top of the stairs and a 12X20 downstairs in the ceiling... the furnace is sucking the air filters strongly.... the guy even said he had not seen one being pulled like this... that is why they are suggesting either one larger return in our game room or three smaller ones in the bedrooms... This only helps on the upstairs... we will have to see what they can do for downstairs...


I just checked and the temp difference is 7 degrees.... so it is worse than I thought it was...
Well, we have return vents in each room (minus baths and kitchens, you don't want cooking and 'other' odors sent through the house - but then they add one to halls). So in rough terms, the returns (air being returned to the furnace/AC) should add up to about the same size as the supplies (the vents that supply conditioned air to the rooms).

But if the upstairs is still warm, I'd close all the supply vents and see what happens. Check that the furnace (Nat Gas I assume?), both before and after, isn't shutting down from over-temp due to low air-flow. If not, I can't see any reason to not just close them all upstairs - why push more heated air into a room that is already warm?

If this is a fairly constant temperature difference, I don't think you will gain anything with automatic vents - they will just 'automatically' stay closed all the time! You can do that manually. You will need to switch for the cooling season, but it's not like that is a lot of effort.

I'm surprised that running the fan at the "ON" setting doesn't help. I tend to do that sometimes in summer, the thermostat is downstairs, so on a moderately warm night, the sinking cool air can keep the AC off, and it just keeps getting warm upstairs. Roughly what % of the time is your furnace running (ON time divided by ON plus OFF time)? In very cold weather, I'm still only around 60% ON.

With that in mind, another 'band aid' option is a remote or relocated thermostat. If you tend to be on one level, just keep that one level comfortable. I think there are some pretty cheap wireless units available now (The NEST is the high-end one).

-ERD50
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Old 02-11-2014, 09:52 PM   #17
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No advice on what you propose, but a horror story for you to watch out for. 35 years ago, we had installed one of the first truly high efficiency heating systems (claimed about 95%). The installer did okay setting the unit (outside) but we caught his "guys" installing the duct work. Instead of strapping and sealing the duct work, they simply slammed nails through the sides of the metal work (leaving holes the length of the runs of duct work). I made the head "guy" rip it all out and do it right. They tried to tell me it didn't matter. I begged to differ (with a veiled threat of a law suit.) YMMV
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Old 02-11-2014, 10:47 PM   #18
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I just checked and the temp difference is 7 degrees.... so it is worse than I thought it was...
You have a similar size house to mine (2800 sq ft) and we have almost the same problem. Is your heating system in the attic or the basement?

My issue is reverse, for heating it's colder upstairs vs. downstairs about 2-7 degrees at times, the system is in the basement. This seems counterintuitive. I've had several HVAC guys look at it, claim I have the ideal duct install, all main trunk metal, dampers everywhere, proper returns and fan on too. I've replaced all my upstairs windows, in the attic I added R30 on top of the old insulation, guessing it was R13-19. Just replaced my gas furnace 2 weeks ago and the only thing the HVAC guys suggested was to add an additional blower to one room that is the coldest, this room butts up/sits on part of a non heated garage. I need to cut out the drywall and insulate that cavity. Adjusted my dampers, but they might deflect 80% at best (I have the 1st fl bath 100% off, but there's still good heat flow coming out). Best I can get the 2nd floor is 2 degrees below the 1st floor when the heat is running on high (2 speed heat), but then drops back 4-7 degrees when it's not on, fan runs all the time.
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Old 02-11-2014, 10:55 PM   #19
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Making the existing system pull it's weight and get the job done is priority, but if it won't work, I have seen these recommended:

Cost Effective Heater | Comfort Cove | Radiant Systems

Wiring would be needed, of course.
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Old 02-12-2014, 10:19 AM   #20
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You have a similar size house to mine (2800 sq ft) and we have almost the same problem. Is your heating system in the attic or the basement?

My issue is reverse, for heating it's colder upstairs vs. downstairs about 2-7 degrees at times, the system is in the basement. This seems counterintuitive. I've had several HVAC guys look at it, claim I have the ideal duct install, all main trunk metal, dampers everywhere, proper returns and fan on too. I've replaced all my upstairs windows, in the attic I added R30 on top of the old insulation, guessing it was R13-19. Just replaced my gas furnace 2 weeks ago and the only thing the HVAC guys suggested was to add an additional blower to one room that is the coldest, this room butts up/sits on part of a non heated garage. I need to cut out the drywall and insulate that cavity. Adjusted my dampers, but they might deflect 80% at best (I have the 1st fl bath 100% off, but there's still good heat flow coming out). Best I can get the 2nd floor is 2 degrees below the 1st floor when the heat is running on high (2 speed heat), but then drops back 4-7 degrees when it's not on, fan runs all the time.

We do not have basements down here in the swamplands of Houston....


I do not see where the placements make a difference if they have adjusted the ducts correctly.... IOW, if I only have ducts going downstairs, I would think that my downstairs would be the hot zone...



We will see what the second guy says... should be here in a couple of hours... I will then call and get a third opinion...
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