Replace duct work when replacing HVAC/heat pump

[jocdoc]

[Topic is now in Personal Consumer Issues - mod mkc]

I will replace my 20 yr old Heat pump. I have a single family home ranch style with my office two degrees F warmer than the living room. It is the most distant to the air handler. All of the HVAC companies that gave me estimates told me that the duct work is fine and doesn't need to be replaced.

It seems logical to me that since the duct is 20 years old it likely has developed microleaks in the flexible ducts or partial loss of seal of those ducts or the ducts may not be the right size for optimal use of the new equiptment. That being said replacing the Duct work would cost $7500 on top of the estimate to replace my heat pump and air handler.

Did anyone replace their ductwork when they replaced their HVAC if there was nothing in particular wrong prior to replacing the heat pump?

[Marq1]

since the duct is 20 years old it likely has developed microleaks

Sheet metal does not "develop" micro leaks, any leaks you have were there from day one!

Did you ever seal up the joints with elec putty or mylar tape 20 years ago? Then you have had leaks for all this time!

[ladycat]

When we replaced our HVAC a few years ago, we did not replace any duct work. It is rigid metal, wrapped with insulation. When they did the air leakage test after the new system was installed, it was something like 7%. The HVAC installers said new systems sometimes aren't even that good. The duct work was at least 30 years old, maybe older.

[RickBoglehead]

It's crazy to replace any ductwork. Any reliable HVAC company could test for leakage if necessary, but as has been said, this is likely a non-issue. You're warmer because the thermostat is in the other part of the house?

[StevieG72]

I replaced my ductwork, it was in bad shape. I also have a room that is the furthest from the air handler. It is still cooler than other rooms in the house in the winter.

You could very likely replace that ductwork and have the same temp issues as before. If all the companies are saying it is fine, it probably is! Otherwise, they would jump at the chance to charge you more. The majority of that cost is labor.

Money would probably be better spent on a dehumidifier, small portable unit that exhaust s out a window, or a ceiling fan.

[tony17112acst]

I do not recommend replacing your duct work!

All joints should have been sealed with duct mastic (which is rubbery when it dries) when it was installed. Most companies skip this step because homeowners are unaware. But you probably don't need it if you've been OK all these years.

Whoever installed the original duct work did not do a good job with "balancing." Do a search on balancing. A simple damper can be put into the duct that keeps the room 2 degrees warmer to restrict air flow a little bit and can be adjusted until you get the perfect mix/temps. You can balance room sometimes with the adjustable vent on the floor/ceiling, but since it produces noise, a damper inside the ductwork (mentioned above) is usually the propert way to balance rooms.

[jocdoc]

I appreciate the responses. My question on microleaks,deteriorating seals is on the flexible hosing that originate from the main sheet metal duct work to the individual rooms.

[inverter]

I appreciate the responses. My question on microleaks,deteriorating seals is on the flexible hosing that originate from the main sheet metal duct work to the individual rooms.

You don't really need to replace it unless it's dirty or broken.

[Pdxnative]

If you’re worried about air sealing the ductwork look into something like aeroseal. It’ll seal them without replacing, and much cheaper.

[SnowBog]

You're warmer because the thermostat is in the other part of the house?

Recently had furnace/heat pump replaced (no changes to ducts). New one has a "smart" thermostat that let's us connect multiple sensors. It's crazy to see the temp variations throughout the house. But it makes sense, further from the heat source...

With our thermostat we can pick which rooms (sensors) to prioritize (or let it do so based on being occupied). This has made a marked difference to comfort.

[cheese_breath]

You may want to install duct boosters in the colder rooms.
https://www.amazon.com/duct-booster-fan ... ooster+fan

[jabberwockOG]

If HVAC system produces different temps in some areas the most likely cause of the issue (assuming overall HVAC system is correct sized) is due to restricted or inadequate airflow in one or more areas. HVAC airflow consists of two separate and discrete components 1) output air vents, and 2) return air vents. Both of these need to be sized and balanced to each other in terms of total airflow as well as location. The larger the home the more this matters.

Output vents need to be placed correctly and adequately sized in each room/area. The placement and sizing of return air vents is equally important. Many homes have inadequate and poorly placed venting for the HVAC system because few installers take the time and effort to do it correctly.

Adding duct work to support/add additional output vent(s) and return air vent(s) to better size and balance the HVAC system airflow can correct a lot of home HVAC issues.

[SaveStrong]

All joints should have been sealed with duct mastic (which is rubbery when it dries) when it was installed. Most companies skip this step because homeowners are unaware.

OP you can buy a whole tub of mastic for ~ $7 and apply by hand (with gloves) or putty knife. super easy DIY and will make a difference

[tibbitts]

Single family ranch suggests flexible ducts to me and the OP mentioned them, although anything is possible. That would include underfloor in-slab ducts - good luck replacing those for $7500.

Over about 20 years my limited experience has been that insulation on flex ducts has increased (it's thicker now), so newer would show an improvement with replacement. But beyond that the massively high temperatures some flex ducts are exposed to can cause them to deteriorate over time, so I don't think regular replacement would be unwarranted. It's not unusual to see duct replacement in homes where I live.

For the OP's problem with a specific room it might be beneficial/trivial to increase that duct size when doing the rest of the work, but I don't have the experience or expertise to know that. Sometimes a plenum is maxed out as-is so that could be another expense.

[Watty]

I have seen housing being built and they install the ductwork before they put the flooring in when everything is accessible and several people can work on a section at the same time.

I have spent days in my crawlspace adding insulation where there was not any and that is miserable cramped work.

If you hire people to do it, even if they try to to do a good job it will be difficult so tearing out the ductwork and replacing it risks ending up with worse ductwork than you started with.

Obviously any problems should be fixed but unless the ductwork was something like 50+ years old and failing because of its age there is no reason to preemptively replace it.

If you do have some minor leaks in the ductwork then you should also need to consider what happens to the hot or cold air in the crawlspace. In effect it heats or cools the crawl space which heats or cools the flooring so the energy is not completely lost. If there was a air leak in the attic the energy would be lost through the roofing.

[tibbitts]

If you do have some minor leaks in the ductwork then you should also need to consider what happens to the hot or cold air in the crawlspace. In effect it heats or cools the crawl space which heats or cools the flooring so the energy is not completely lost. If there was a air leak in the attic the energy would be lost through the roofing.

It would help for the OP to clarify what type of installation this is.

[jerrysmith]

You may want to install duct boosters in the colder rooms.
https://www.amazon.com/duct-booster-fan ... ooster+fan

We bought one of these for my son's room and it worked wonders.

[Cletus Davenport]

If the difference between your warmest and coldest room is only 2 degrees. You’re doing pretty good. I don’t think that replacing or trying to better seal your ducts will make any difference at all.

Dampers might, but might not…..

I’m not an AC expert but my guess is that to make it “equal everywhere” will cost more money than you’d ever want to spend. And there still are no guarantees, you might still have a difference.

[dcabler]

Looked at it briefly when we replaced our HVAC 2 years ago - cost was on par with the HVAC itself. We passed.

[tibbitts]

Looked at it briefly when we replaced our HVAC 2 years ago - cost was on par with the HVAC itself. We passed.

Post-COVID it seemed very difficult to find flex duct for a while, so that might have affected estimates at the time. Presumably not so much by 2023, though, although I don't know if prices ever partly recovered.

[dcabler]

Looked at it briefly when we replaced our HVAC 2 years ago - cost was on par with the HVAC itself. We passed.

Post-COVID it seemed very difficult to find flex duct for a while, so that might have affected estimates at the time. Presumably not so much by 2023, though, although I don't know if prices ever partly recovered.

Quite possible - then I look at my electric bill which was <$100 last month and rarely tops $250 in the heat of summer in Central TX.

[Catalina25]

If your duct work is out of balance it may result in an imbalance in the air temperature within the house.

In my ranch home, the duct dampers furthest from the HVAC unit are fully open with the ones closest to the unit being something less than fully open to have a more balanced temperature throughout the house. If all the vent dampers were fully open, the warmest/coolest air would come out of the nearer vents with more force and temperature leaving the furthest vents with a trickle of air flow. By restricting the nearer vents somewhat, I can increase the airflow to the vents at a greater distance from the HVAC unit so that the airflow is better equalized throughout the house.

[tibbitts]

If your duct work is out of balance it may result in an imbalance in the air temperature within the house.

In my ranch home, the duct dampers furthest from the HVAC unit are fully open with the ones closest to the unit being something less than fully open to have a more balanced temperature throughout the house. If all the vent dampers were fully open, the warmest/coolest air would come out of the nearer vents with more force and temperature leaving the furthest vents with a trickle of air flow. By restricting the nearer vents somewhat, I can increase the airflow to the vents at a greater distance from the HVAC unit so that the airflow is better equalized throughout the house.

It may depend if, like many hvac systems, the minimum required airflow requires the maximum possible airflow through every available vent.

[Catalina25]

If your duct work is out of balance it may result in an imbalance in the air temperature within the house.

In my ranch home, the duct dampers furthest from the HVAC unit are fully open with the ones closest to the unit being something less than fully open to have a more balanced temperature throughout the house. If all the vent dampers were fully open, the warmest/coolest air would come out of the nearer vents with more force and temperature leaving the furthest vents with a trickle of air flow. By restricting the nearer vents somewhat, I can increase the airflow to the vents at a greater distance from the HVAC unit so that the airflow is better equalized throughout the house.

It may depend if, like many hvac systems, the minimum required airflow requires the maximum possible airflow through every available vent.

Maybe, but years ago, while watching This Old House, they had an episode on balancing a forced air system in which they did basically as I described above to balance the airflow throughout the house.

HVAC Air Balancing: What You Should Know

[tibbitts]

It may depend if, like many hvac systems, the minimum required airflow requires the maximum possible airflow through every available vent.

Maybe, but years ago, while watching This Old House, they had an episode on balancing a forced air system in which they did basically as I described above to balance the airflow throughout the house.

HVAC Air Balancing: What You Should Know

I don't think it will work properly if the total CFM the ductwork is capable of only matches the furnace minimum requirement - which is mostly what I've been familiar with. In my case the furnace is the air handler for the air conditioner and the coil needs a certain amount of airflow to avoid problems. But I could be wrong so hopefully someone who knows definitively will explain.

[brennok]

Check with your local electric company first. Ours offers a home audit for free and depending on results they offer discounted or free air duct sealing.

[criticalmass]

Did anyone replace their ductwork when they replaced their HVAC if there was nothing in particular wrong prior to replacing the heat pump?

Replacing duck work is a wasteful make work sales job unless the original duct is grossly undersized. Any sheet metal leaks can be repaired easily.

[criticalmass]

Did anyone replace their ductwork when they replaced their HVAC if there was nothing in particular wrong prior to replacing the heat pump?

Replacing duck work is a wasteful make work sales job unless the original duct is grossly undersized. Any sheet metal leaks can be repaired easily.

[tibbitts]

Did anyone replace their ductwork when they replaced their HVAC if there was nothing in particular wrong prior to replacing the heat pump?

Replacing duck work is a wasteful make work sales job unless the original duct is grossly undersized. Any sheet metal leaks can be repaired easily.

But at least some if not all of the OP's ducts are not made of sheet metal; they're made of thin plastic and other materials that are known to deteriorate over time, especially when subject to extreme temperature conditions.

[criticalmass]

Replacing duck work is a wasteful make work sales job unless the original duct is grossly undersized. Any sheet metal leaks can be repaired easily.

But at least some if not all of the OP's ducts are not made of sheet metal; they're made of thin plastic and other materials that are known to deteriorate over time, especially when subject to extreme temperature conditions.

If the materials had deteriorated enough to be leaking, they would be leaking. Are they failing?

[tibbitts]

But at least some if not all of the OP's ducts are not made of sheet metal; they're made of thin plastic and other materials that are known to deteriorate over time, especially when subject to extreme temperature conditions.

If the materials had deteriorated enough to be leaking, they would be leaking. Are they failing?

In my neighborhood I've seen old ductwork that's being discarded and either the outside covering has deteriorated exposing the insulation (which then has nothing to hold it to the duct), or the inside has deteriorated and is flaking off (and being blown out the ducts, I'm guessing.) If you search on "gray flex duct problems" you'll see examples of this.

[criticalmass]

If the materials had deteriorated enough to be leaking, they would be leaking. Are they failing?

In my neighborhood I've seen old ductwork that's being discarded and either the outside covering has deteriorated exposing the insulation (which then has nothing to hold it to the duct), or the inside has deteriorated and is flaking off (and being blown out the ducts, I'm guessing.) If you search on "gray flex duct problems" you'll see examples of this.

I would replace if failing and not replace if not failing.

[DarkHelmetII]

My non-expert opinion: two degrees differential is pretty good (as others have said). Likely not worth time / money / hassle and may end up with something worse .

[MtnTravel]

Did anyone replace their ductwork when they replaced their HVAC if there was nothing in particular wrong prior to replacing the heat pump?

I had same issue and solved it when we got a Mitsubishi ducted heat pump where the blower runs 24/7. The house is now a consistent temperature because the air is constantly circulating.

I wouldn’t mess with duct work. There’s no guarantee adding or moving ducts is going to fix the problem.