I’m getting estimates to retrofit my 1919 house in Oakland, converting from 3 floor furnaces to central gas heat. I have one lowball estimate, one high estimate, and one mid-range estimate (with two more that are supposed to send me their quotes by the end of the week). The high-end quote is twice the low end!
All of the companies have good reputations in the area and have been in business upwards of 40 years. The biggest difference seems to be that the expensive company actually took measurements and did a load calculation (although he came up with a size that is in line with the others by rule-of-thumb), and he emphasizes that his company ONLY uses alumaflex, not the plastic flex coil for ducting.
Question: How big of a deal is plastic vs aluminum supply ducts? He told me the ductwork accounts for 1/3 of the price he quoted me, and roughly equal to the difference between his quote and the next one lower. Is the plastic ductwork satisfactory, or will I be sorry if I go with it?
Thanks for any advice.
Replies
Be clear on the terms, because there are more than two types of flex duct. Other than a very short lengths to connect the dryer vent, corrugated aluminum duct (insulated or not) is not often used in air distribution. Foil flex is more common, which is plastic but it has a silvery, relfective outer covering. The R-value is important. R-4.2 is the old standard, R-6 is quickly becoming the new standard. Regardless of the type of flex, keep the use of it to a minimum.
Plastic flex duct is like vinyl siding; it can be a great cost saving material with little or no reduction in quality (opinions on this will vary greatly) IF used according to good practices. They both, however, allow unqualified individuals to get by without having any skill or experience, do so at a lower price, and the HO gets stuck with substandard work.
When comparing the estimates be sure to also closely consider the following:
Compare features, warranties, capacities and efficiencies of the equipment.
Compare the features and details of the "extras" like the thermostat, filter, humidifier, fresh air provisions, etc..
Compare the guarantee/warranty of the installation. If one installer will stand behind their work, unconditionally, parts & labor with no service fees, for at least a year and one will simply offer you the manufacturer's parts warranty, there is a significant difference.
Thanks, Tim. That helps a lot.
I'm interested to hear the responses here==
I helped a friend (and HVAC guy) on his house last winter, and we put in all flex duct....it was a plastic type with plastic wrapped fiberglass insolation, probly 10 inch stuff
He thought it was the best thing since sliced bread--?????? thoughts?
Great post Tim.... concise and lots of good information. I'm dealing with a similar situation myself, so I appreciate it.
TimWhat is you experience with life spans and deterioration over time of the various products?
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Sojourners: Christians for Justice and Peace
"What is you experience with life spans and deterioration over time of the various products?"
I have surveyed a system that had 20 plus year old flex installed and the was no significant deterioration of the product (the flex duct) but, the tape that once held the flex to the sheetmetal trunk takeoff had disintengrated and the duct had become disconnected. That is the oldest installed flex that I have examined.
I have never seen a job where aluminum flex duct was used in a supply system, though I have seen it used in bathroom exhaust and dyer vent applications. I have never seen degradation of aluminum flex in the field. The insulating jacketing is usually damaged during installation, if damaged at all. As with the plastic (they are actually made of a double-ply polyester core with a polethylene jacket) flex, the connections are the weak point.
I have worked with pre-insulated 10 foot lengths of aluminum flex duct. Much more rigid than what you can get at the local big box, not cheap, either. Given a choice between the aluminum and plastic flex, money no object, I would choose aluminum.
Plastic flex duct will become brittle in time in an attic.
Plastic flex duct can be crushed easily.
Those plastic ties that hold the whole thing together also get brittle.
Those cheap #### contractors that use duct tape instead of ties... well, we all know what happens to duct tape.
Critters like to munch on it.
If it gets wet, it will never dry out.
Flex duct has its place... it is acceptable if lengths are kept reasonable (like around 5 feet) and if it isn't buried in a wall or ceiling. I would never use it in a location that will be inaccessible later.
As mentioned already, there are many variables behind the final bid. Find out what they are, and ask for references.
My thoughts on flex duct.... Its garbage. I go with my sheet metal guy that only uses hard pipe. There is a profound difference in air friction and a profound leap in efficiency of the ducting when using hard pipe.
Wow, there sure are a lot of opinions on this one. Well I'll add mine.
Flex duct is a very useful tool in the arsenal. Flex comes in 25' lengths and if properly attached to the plenums and buckets with mastic it can be part of a very tight duct system. In all systems, it is necessary to use flex at the bucket tie-in to kill the noise of vibration that is transmitted through metal ductwork. There are some brands that are much higher quality and durable than others.
Metal ductwork must be sealed with mastic every 5' and along the length of each seam. This is often poorly done because it is either not sealed at all or it is simply painted on instead of being properly worked into the seams. Metal duct must also be externally wrapped and covered with a vapor barrier. In cooling applications, a poorly executed vapor barrier will allow the insulation to become saturated. My point is that any product can be poorly done.
All ductwork should be located within the conditioned space. In doing so, the durability of any product will be extended. I believe that good quality flex, istalled within the conditioned space and protected from damage will last 50 years. The issue then becomes how to maintain the cleanliness of the interior liner. 4" pleated filters will vastly improve the quality of the filtration when properly fitted and maintained.
The quality of an HVAC installation is not tied to the use or non-use of flex duct. I have installed systems that were professionally drawn by mechanical engineers that included liberal use of flex duct in multi million dollar homes. The more important questions involve proper sizing of ductwork and equipment, installation of efficient equipment, and proper installation of the well designed plan. Ask for references of recent work.(within the last two months) It is important that you consider this carefully.
>>In all systems, it is necessary to use flex at the bucket tie-in to kill the noise of vibration that is transmitted through metal ductwork.Bucket tie-in? Whaz dat?FWIW, I inspect a lot of older homes with all metal ductwork that don't seem unusually noisy.>>will last 50 years.>>The quality of an HVAC installation is not tied to the use or non-use of flex duct. I have installed systems that were professionally drawn by mechanical engineers that included liberal use of flex duct in multi million dollar homes.Do those plans include use of flex duct in inaccessible areas? Can a multi-million dollar home be considered a quality job if the walls have to be torn open in 50 years (or perhaps less?) to replace a wornout component?
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Sojourners: Christians for Justice and Peace
That's texas hick for register connection.
In answer to your other two questions, yes and yes.
In designs that I have influence on, I try to have access to all ductwork but it is expected that in 50 years a home will need a remodel that will include some drywall. Metal ductwork will need inspection and repair at some point in it's life cycle as well. It is a good idea to use metal ductwork in inaccessible areas for cleaning purposes. It is also a good practice to install metal ductword in a manner to allow for future cleaning. Both products have their place and neither indicates a low quality job.
Duct board should never be used in the airstream. It does make a good spacer in some applications such as when a duct needs to be isolated from a recessed can or in some similar situation.
I've heard of mastic for tile jobs, not for duct work. What kind of mastic is being referred to?And is there anywhere one can read up on this stuff? At this point the ductwork is in, I just want to try doing the things that the installers left out....
Click here-http://www.google.com/search?hl=en&q=%22duct+mastic%22
Here's a REALLY informative web site:http://hphaa.com/services/installation/installation.htmRebeccah
As someone above said, plastic flex duct is wonderful.
If you upsize one size over metal duct, it moves the same amount of air.
The most important aspect is that it is sealed better than metal duct when installed.
Where I live plastic flex duct is the standard for new construction - doesn't matter the cost of the house - or at least as far as I know. R6 insulation is now required here - used to be R4.2. I can't imagine that the difference in price would even add up to $100 for a house. Something that was touched on above - whatever HVAC company you think you want to use - tell them you want your duct system sealed with mastic both the flex duct connections and the sheet metal plenums. HVAC companies install duct systems with between 1 and 20 % leakage, and that can add a lot of wasted monthly heat bill money unless all your duct work is within the conditioned space.
You may also want to discuss with a contractor that you are seriously considering about how many supplies and returns he wants to install. Generally, more is better as it results in better air distribution.
BTW - it sounds like you have gotten (or in the process of) 5 estimates. There is a lot of bad press around here about free estimates. It's called wasting contractor's time, and also accounts for part of the high price of products and services purchased from contractors. Please think about this before you decide to get more people involved. The contractor's who have not gotten back to you may or may not. People tend to develop a "radar" for this type of situation.
Where I live plastic flex duct is the standard for new construction - doesn't matter the cost of the house - or at least as far as I know. R6 insulation is now required here - used to be R4.2. I can't imagine that the difference in price would even add up to $100 for a house. Something that was touched on above - whatever HVAC company you think you want to use - tell them you want your duct system sealed with mastic both the flex duct connections and the sheet metal plenums. HVAC companies install duct systems with between 1 and 20 % leakage, and that can add a lot of wasted monthly heat bill money unless all your duct work is within the conditioned space.
Or, I could wait until October when Califrnia's Title 24 regulations go into effect and contractors are required to test their work and achieve < 4% leakage...
You may also want to discuss with a contractor that you are seriously considering about how many supplies and returns he wants to install. Generally, more is better as it results in better air distribution.
Last week, I downloaded a copy of hvac-calc to get an idea of my heating loads on a room-by-room basis. Everyone seems to just be assuming one register per room will be fine, but from my calculations, the living sees twice as much heat loss and the next highest room, and more than can be readily replaced through one register. So, I'll definitely be discussing this.
BTW - it sounds like you have gotten (or in the process of) 5 estimates. There is a lot of bad press around here about free estimates. It's called wasting contractor's time, and also accounts for part of the high price of products and services purchased from contractors. Please think about this before you decide to get more people involved. The contractor's who have not gotten back to you may or may not. People tend to develop a "radar" for this type of situation.
I was planning to get 4 estimates, not 5, but the 4th company took so long to get back to me that I ended up looking for another -- and then the 4th company, which I really was interested in (and still am), finally came through.
The "too many bids" problem is a hard one to avoid when one is a cautious shopper.
I would have been more than happy to have someone do a *paid* estimate, if they would do the calculations and provide me with a detailed report. Structural pest control companies do that all the time. They call it a structural pest inspection, and it still may not completely cover their costs (I think I paid $240), but it's something.
>> Or, I could wait until October when Califrnia's Title 24 regulations go into effect and contractors are required to test their work and achieve < 4% leakage... <<
That is pretty interesting... I hope it catches on and similar legislation is adopted in many states. I found a web page with info about Calif Title 24 regs:
http://www.energy.ca.gov/title24/2005standards/index.html
and a summary at:
http://www.energy.ca.gov/title24/2005standards/2005_SIGNIFICANT_CHANGES_2P.PDF
It definately sounds like you are doing your homework...
>> Last week, I downloaded a copy of hvac-calc to get an idea of my heating loads on a room-by-room basis. Everyone seems to just be assuming one register per room will be fine, but from my calculations, the living sees twice as much heat loss and the next highest room, and more than can be readily replaced through one register. So, I'll definitely be discussing this. <<
You probably already know this but often they will upsize the register and associated duct for such a room. Personally, I'd rather see 2 supplies for better air distribution.
Likewise some rooms may have meager requirements - for example I was building some houses with an interior bathroom (no windows or exterior walls) and the recomendation was to cut back the duct damper for this room for very little airflow. The HVAC guys I was using seemed to have some trouble with this concept... but I won't go through the whole story.
BTW - I'm a builder type - not an HVAC guy...
Edited 8/28/2005 8:27 pm ET by Matt