[mnoone]

I am getting ready to have a new HVAC system installed in my house. I've had 4 different companies come out to quote the work. Normally I'd have two come out - but I just didn't get a good vibe from the first three. The 4th I actually liked though. My house is 1600 square feet and I currently have a 30 year old central furnace that works fine that is using 60 year old rigid ducting throughout the house.

First and second vendors want to add a couple new vents (go from 9 to 11), and expand my two 2x14 boots to 4x14 (the rest are 4x14). They also both wanted to increase my return duct from 14" to 16" diameter

Third vendor wants to tear out all my old rigid ducting and replace it all with flex. Not sure about sizing. Also mentioned adding at least one vent.

Fourth vendor wants to tear out all ductwork, replace it all (with new rigid), and add 7 vents (go from 9 to 16).

All of them are quoting ~3-4 ton ACs, and 60-80KBTU furnaces. This is in Northern California.

The fourth vendor is the only one who took floor plan and ran calculations with some sort of software (didn't catch the name - but some sort of specialized HVAC software). The others seemed to just use some rule of thumb to size furnace and AC.

So - my questions:

• Does 16 registers seem like a lot for a 3.5 ton AC?
• My current furnace works fine (with 14" return and 9 registers). Does it make sense that I would need to enlarge return and add more registers to add cooling?
• If it does make sense - why couldn't I just enlarge the ductwork going to the vents but not add so many vents? Would it get noisy?
• What can I do as a homeowner to make sure these guys are sane?

 

[firecontrol]

From reading your post I'd guess you've already answered your own questions and it is coming down to justifying the added cost for the last guy's quote.

By asking here what we think about adding registers, enlarging duct or if the system would make more noise or not you're asking for the same kind of information you got from the first 3 people. Why? Because we're not there, can't see the house, can't make the measurements and do the math required and will only be able to give you suggestions and educated guesses.

It sounds to me like the last company did the right things and is making a recommendation on their experience, first hand knowledge of you and your home and what they believe will give you the best value for you investment.

As for if they are sane or not........... Ride along with a service tech for a week or two. See what the average HVAC person deals with on a daily basis and I think you'll realize we're all a bit "different" from the average person you'll meet. Now I wouldn't call that sane or not, but it does tend to give us a sense of humor that only another HVAC person understands.

 

[pecmsg]

From reading your post I'd guess you've already answered your own questions and it is coming down to justifying the added cost for the last guy's quote.

By asking here what we think about adding registers, enlarging duct or if the system would make more noise or not you're asking for the same kind of information you got from the first 3 people. Why? Because we're not there, can't see the house, can't make the measurements and do the math required and will only be able to give you suggestions and educated guesses.

It sounds to me like the last company did the right things and is making a recommendation on their experience, first hand knowledge of you and your home and what they believe will give you the best value for you investment.

As for if they are sane or not........... Ride along with a service tech for a week or two. See what the average HVAC person deals with on a daily basis and I think you'll realize we're all a bit "different" from the average person you'll meet. Now I wouldn't call that sane or not, but it does tend to give us a sense of humor that only another HVAC person understands.

^^^^^^^^^^^^^^^^^^^^^^^^^^ X - 2^^^^^^^^^^^^^^^^^^^^^

 

[mnoone]

From reading your post I'd guess you've already answered your own questions and it is coming down to justifying the added cost for the last guy's quote.

By asking here what we think about adding registers, enlarging duct or if the system would make more noise or not you're asking for the same kind of information you got from the first 3 people. Why? Because we're not there, can't see the house, can't make the measurements and do the math required and will only be able to give you suggestions and educated guesses.

It sounds to me like the last company did the right things and is making a recommendation on their experience, first hand knowledge of you and your home and what they believe will give you the best value for you investment.

As for if they are sane or not........... Ride along with a service tech for a week or two. See what the average HVAC person deals with on a daily basis and I think you'll realize we're all a bit "different" from the average person you'll meet. Now I wouldn't call that sane or not, but it does tend to give us a sense of humor that only another HVAC person understands.

So the fourth company is asking for almost twice what the other three companies are asking for. That's... a lot of money... And this is NorCal prices which are already obscene (I don't think we're supposed to post prices - so let's just say that I could almost buy a brand new BMW for what the 4th company is quoting). They were more thorough but you would think that at least one of the other three companies would have noticed that I needed a pile of new vents if they were really critical. My suspicion is that I can get away without the new vents but I'll have a happier system with the new vents. So the first three companies are trying to get my system functional, while the last is trying to get my system perfect. It's unclear how critical this perfection is (and if that perfection is worth the much higher price tag).

 

[BNME8EZ]

I don't know what your normal energy bills are but at 3.5 ton I would assume they are not inexpensive. You ask if it is worth the extra money, would saving 10% on energy bills be worth the money, especially being more comfortable at the same time?

This is the part most people don't understand. We hear all the time my old system worked fine, why do I need to upgrade my duct system, this while we are there replacing a safety control. Safety controls are there to shut the system down before it gets too far out of normal operating conditions. If a safety works to the point of failure then there is a problem with that system. A problem that is causing repairs to the system, higher energy bills and varying degrees of discomfort for the customer. Most owners don't realize that their unit is operating on one of the safety controls until it fails and they need a tech out.

As far as your situation goes, we don't know any of the contractors involved. They may be very good or they may do as cheap of job as fast as they can,collect the money and run. We don't know. My suggestion is to get a list of customers and see how happy they are with the work done. Did they end up with the same results they had before or was it a improvement over the past system. If you can take a look at the job done, does it look like great care was taken or did it get thrown in as fast as possible. Ultimately the decision is yours so you need to educate yourself on the product each dealer puts out and decide from there.

 

[mnoone]

I don't know what your normal energy bills are but at 3.5 ton I would assume they are not inexpensive. You ask if it is worth the extra money, would saving 10% on energy bills be worth the money, especially being more comfortable at the same time?

This is the part most people don't understand. We hear all the time my old system worked fine, why do I need to upgrade my duct system, this while we are there replacing a safety control. Safety controls are there to shut the system down before it gets too far out of normal operating conditions. If a safety works to the point of failure then there is a problem with that system. A problem that is causing repairs to the system, higher energy bills and varying degrees of discomfort for the customer. Most owners don't realize that their unit is operating on one of the safety controls until it fails and they need a tech out.

As far as your situation goes, we don't know any of the contractors involved. They may be very good or they may do as cheap of job as fast as they can,collect the money and run. We don't know. My suggestion is to get a list of customers and see how happy they are with the work done. Did they end up with the same results they had before or was it a improvement over the past system. If you can take a look at the job done, does it look like great care was taken or did it get thrown in as fast as possible. Ultimately the decision is yours so you need to educate yourself on the product each dealer puts out and decide from there.

I don't have AC right now, just heating. My heating bill is a few hundred a month in the winter. It would take a very, very long time for any cost savings in heating/cooling bill to be more than the price difference between the first three and the fourth vendors. So I do not think looking at cost savings is the way to go here. It's more about looking at reliability, comfort (as in, not having to deal with constant cycling), noise, simply functionality, etc.

All 4 companies have very good reviews.

Can anybody point me towards any guides on sizing ductwork?

 

[BNME8EZ]

If you don't have A/C now then the duct becomes more important. It is harder to move cold air than warm air. Most heat only duct is undersized. Actually most duct is undersized to be truthful about it. Partially to keep costs down, partially because of space left by the builder and other trades.

A furnace on bad ducts will cycle on the limit. An A/C on bad ducts will freeze up, run longer than it should, not dehumidify properly and increase your utility bill by an indeterminably amount, just to mention a few issues.

 

[mnoone]

If you don't have A/C now then the duct becomes more important. It is harder to move cold air than warm air. Most heat only duct is undersized. Actually most duct is undersized to be truthful about it. Partially to keep costs down, partially because of space left by the builder and other trades.

A furnace on bad ducts will cycle on the limit. An A/C on bad ducts will freeze up, run longer than it should, not dehumidify properly and increase your utility bill by an indeterminably amount, just to mention a few issues.

Why is it harder to push cold air than warm air?

 

[BNME8EZ]

Warm air is buoyant, cold air is heavy.

 

[mnoone]

Warm air is buoyant, cold air is heavy.

So if ductwork was in the attic, rather than crawlspace, would you need to size the system for the heating, rather than sizing for the cooling?

 

[martyinlincoln]

The duct you have could handle about half of the air flow that AC requires. It does need to be replaced.

 

[Artietech]

We size airflow for the higher of the two. The duct needs to be able to handle moving the right CFM's. Usually the cooling CFMs are higher, ask the contractor HOW they are sizing the duct. ACCA Manual D approved software should be part of the answer.

 

[mnoone]

The duct you have could handle about half of the air flow that AC requires. It does need to be replaced.

Using this chart I agree that the return needs to be enlarged. 3.5 tons means 1400 CFM which means 16" diameter duct minimum, if I'm reading that right.

But again using that chart, I currently have 7 4x14 boots and 2 2x14 boots. That means 7x 200CFM + 2x 100CFM = 1600CFM. I don't know my duct sizes (will double check tonight) - but to me it seems my boots are large enough and that I should not need more - but I might perhaps need to enlarge ducts going to boots. Is this the right way to calculate that?

Thank you!

 

[BALloyd]

Enlarging your register boots will do nothing if your pipes feeding them are too small to begin with.

Old furnace systems needed far less airflow than a modern AC system.

If you like to gamble pic one of the 1st three contractors. If you want it done right and have a comfortable, quiet and efficient system, pic contractor 4.

Sent from my SM-G965W using Tapatalk

 

[pecmsg]

That chart doesn’t take into account balance turns and lengths.
It shows the amount of air a short straight piece of duct that size will handle

 

[mnoone]

Enlarging your register boots will do nothing if your pipes feeding them are too small to begin with.

Old furnace systems needed far less airflow than a modern AC system.

If you like to gamble pic one of the 1st three contractors. If you want it done right and have a comfortable, quiet and efficient system, pic contractor 4.

Sent from my SM-G965W using Tapatalk

What I'm getting at is - do I actually need more boots? Or can I just make sure all the ducts going to the boots are 8" diameter?

Vendor #4 is saying I need 16 4x14" boots which suggests to me that he wants 3200CFM airflow... which seems like massive overkill but this is obviously not my profession...

 

[pecmsg]

What I'm getting at is - do I actually need more boots? Or can I just make sure all the ducts going to the boots are 8" diameter?

Vendor #4 is saying I need 16 4x14" boots which suggests to me that he wants 3200CFM airflow... which seems like massive overkill but this is obviously not my profession...

It doesn’t work like that.

Please you need someone on sit that knows duct systems.

 

[mnoone]

It doesn’t work like that.

Please you need someone on sit that knows duct systems.

Can you please explain where I have made a mistake? Or if there is a good resource on duct planning I'm happy to work my way through that.

 

[pecmsg]

Can you please explain where I have made a mistake? Or if there is a good resource on duct planning I'm happy to work my way through that.

It’s called your contractor!

 

[mnoone]

It’s called your contractor!

I'm trying to choose one. That is the problem. Repeatedly telling me to ask a professional is unfortunately not helpful right now as I am trying to *choose* a professional. I recognize that people on this forum are sensitive to DIYers as they represent a loss of business so DIYing is heavily discouraged - but that is not my goal here. I have little interest in doing my own system. I just want somebody to do my system well and for a fair price.