Central Air Retro in Simple Ranch
I’m now in the 4th year of gutting and remodeling my small ranch in MA. My wife decided that it would be a good idea to have central A/C installed. While I will tackle many projects and all the carpentry I know nothing about A/C.
I figure someone out there would be able to tell me what level of difficulty from a broad sense this job would be.
The house is a single level ranch, simple 40’x26′ foundation. Well insulated attic space and finished basement with drop ceiling. Oil hot water baseboard heat and no current ductwork.
I’m thinking this could be a relatively straight forward installation with ductwork running along the drop ceiling in the basement and coming through the floor. Now I believe I would then need return ductwork in the walls of each room, correct?
Can anyone give me an idea as to the overall complexity and potential price (ballpark tosee if it is in the budget).
Thanks in advance as usual.
SJ
Replies
Steve,
Ideally you would want a return in each room, but not a necessity. The difficulty will come in two places primarily: 1-finding someone to sell you the necessary materials, and 2-connecting/charging the refrigerant lines.
INSTALLED cost of a 10 SEER, 1.5 ton A/C would/should run in the neighborhood of $3K, DIY about $1500.
Thanks Tim
I would pay for install, most things I'll DIY but I'll pay the extra for somone else's time.
Our house should be a straight forward install..........."should" being the operative word there.
SJKnow a little about alot and alot about little.
Sorry, I disagree about the individual returns. Depending on the layout of the house, location of the a-coil, etc, one common return could work well. If the bedroom doors are undercut sufficiently, there is usually enough of a gap to circulate the air even with the doors closed. And some rooms (kitchen) usually don't have doors.
Do it right, or do it twice.
"...I disagree about the individual returns. Depending on the layout of the house, location of the a-coil, etc, one common return could work well."
No , a single return in a house of any layout (btw, the location of the evaporator coil is not a factor in the operation or effectiveness of the return side of the system) over 1000 sf will not work "well". It is a common shortcut/cost cutting installation technique that is just "good enough", but is by no means "good".
A single, centrally located return in a small, single level house will perform as well as most residents have come to expect as adequate. In some cases it is a necessary and/or practical compromise. However, I said, "ideally" individual rooms should have individual returns (excluding bathrooms and kitchens) recognizing the fact that in actual installations, especially in remodel/retrofit applications, "ideal" is not practical.
Tim
Tim,
can you suggest any good sources for learning more about duct system design and pereformance evaluation?_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Bob,
In a word: No.
Most texts on duct and/or system design are not practical for simple systems such as are installed in residential buildings. There are some basic guidelines, but most residential design will depend on the specifics of each installation and the compromises that must be made to keep within budgets and other constraints. I learned what little I know from someone who has design HVAC systems for 35 years.
As far as a performance evaluation goes that would depend on some general basics and the specifics of the installation. The basics would be limited temperature variations within the space (i.e., no greater than 3 or 4 degrees within a room) up to 6 ft above the floor, limited noise and limited drafts. The specifics would have to take into account the compromises as listed above. For instance, if I were evaluating the performance of a variable speed, multizoned system, I would expect a greater consistency than a single zone on/off type of system. The former would obviuosly cost substantially more than the latter. Can the system maintain a minimum tempereature on the coldest winter day in all occupied spaces? Can the system maintain a maximum tempereature or humidity on the worst summer day? Bottom line: is the house comfortable, within reason.
Thanks Tim.
How about aggregate supply register size in relation to aggregate return register size? And, is that affected by aggregate length/size of supply and return ducts?
Is there any simple, practical way to use the scoop that came with my Dwyer draft gauge to form some opinions? E.g., Should I be seeing some minimum reading at each register?
What I'm looking for is something that can be easily integrated into a 2 1/2 +/- home inspection where I can make some fast, efficient and reasonable observations with some degree of assurance/authority.
I don't want to get into situations where I'm saying something an HVAC guy doesn't know about AND I can't back up my statement with objective facts. _______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Bob
You might want to look that the articles in JLC. They have had several different article on HVAC installation and at least one has some very basics on duct sizing and airflow rates.
Bob,
If you are looking for some rules of thumb to estimate if a forced air system is adequate I can offer a few. If you know or have access to a professional installer or designer they should be able to as well.
I would expect no more than 2 sf/cfm in an average home (800 sf/ton) for cooling where you live. 35-50 btuh/sf - heating, typically at 2/3 - 3/4 the cooling flow rate.
The nominal capacity (at 700 fpm) of some standard supply floor registers are:
2x10 - 60, 2x12 - 70, 2x14 - 80, 4x10 - 120, 4x12 - 140, 4x14 - 160
Adequate agregate return grille sizes would be approximately 1 sq.ft/ton.
A panned 2x4 stud space (16"o.c.) is good for up to 150 cfm, a panned 2x12, 16"o.c. floor joist space, up to 750 cfm (returns only).
These would be applicable in the absence of any "extenuating" circumstances.
Tim
If you can, run the conditioned air through the attic, run the returns at floor level.
Go with individual returns. Central returns haven't been used in new construction for over 50 years.
_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Oh Bob, where have you been? All the new homes that are built in the Southwest, since at leasat the 70's through today, have central returns. Ducted returns are unheard of, except in some commercial buildings.Do it right, or do it twice.
Oh Bob, where have you been? All the new homes that are built in the Southwest, since at leasat the 70's through today, have central returns. Ducted returns are unheard of, except in some commercial buildings
Wow! I've been in the Northeast and "midwest" (if NW Ohio is MW.) Central returns are way passe around here.
Is that the best practice or another example of competition leading to less than the best practices?_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Ok, maybe I was sarcastic or something...sorry. I don't know about 'best practice' etc, but here in Texas there are no ducted returns. (Having said that, I'm sure someone will post about a ducted return, but generally speaking...) Most homes have the a/c-heater unit in a closet in the house, more or less centrally located, with ducts run in the ceiling and a return air grill in the wall below the unit. Some houses have the unit in the attic, and then the return air grill is in the ceiling directly below the unit.
Here's a typical installation. The unit is raised off the floor about 24" so the return air can come in a floor level and go up through the unit. (The attic units are usually side draft.) This unit is accessed by a door in the laundry room on the other side of the wall.
Do it right, or do it twice.
Edited 7/25/2003 9:59:58 PM ET by ELCID72
Edited 10/16/2003 8:18:20 PM ET by ELCID72
It's been my experience, that central returns are more the norm than the exception. My experience has mostly been in Arizona. Jim J
Instead of paying someone to install your condenser and the evaporator coil onto your furnace, save some money and do it yourself. You can buy a condenser unit from plumbing/HVAC outlets. Set the concrete base (those plastic pans are a cheap way out), run the electric, tie everything in. String the copper refrigerant tubing through the walls etc. up close to the condenser. The manual that comes with your condenser will give you the tubing sizings - be sure to match it to your evaporator coil. Buy an evaporator coil for your furnace and install it. Most towns have a sheet metal shop that specializes in fabricated condensate pans for evaporator coils and sell to HVAC guys.
Then pay an HVAC tech to braze the copper and vacuum the line for moisture. He may add a little refrigerant if your line lengths are longer than intended by the condenser mfg. - the condensers come precharged these days. So you might pay $70 for labor instead of $1500.
remodeler
You can also look a the mini-duct systems, which would make sense if using hydronic heat. Unfortunately, they aren't cheap. For our 1 1/2 story we were quoted at $9000.
Can I really get ductwork + fan + condensor + ac for $3000 installed? Maybe I need to re-look at a traditional system again...
Seeing as how I have no duct work now and require the full system I think I will looking at more than $3K.
$9000 for mini-duct for 1.5 stories......that sounds like some of the prices coworkers have been looking at. A woman that works for me had quotes ranging from $5-13K for her 2 story 2000sq split level this year. They eventually paid maybe $6000 for their system.
SJ
Know a little about alot and alot about little.
My son just put central air and heat put into an older 2 story home in Virginia that previously had radiators for heat and no A/C. Cost was about 7000+ . Look carefully at what brand of AC unit they want to sell you. Wide variety of quality and prices.
For a home just over 1,000 sq feet one return duct would be fine. In homes of over 2,000 sq feet in Calif they have only one large return duct. But having lived in the desert for far to long in my life and suffered through badly designed and installed A/C units I have found that placement of the return duct is critical. I strongly believe that return air should be pulled from the warmest room of the house in as large of volume as possible. Keep your refrigerant line run as short as the manufacturer recommends not at the other end of the scale. Put a power ventilator in the attic so that air from the cool side of the house is pulled through the atttic and vented out the hot side of the house. Sliding glass doors and large windows with direct sun exposer radiate a great deal of heat into a room. This radiated heat needs to be reduced as much as possible.
I have a 1100 sq ft home in SO Calif with out A/C and will being doing that soon but we will need a roof mounted unit.
In your case I would run the ducts in the basement and use 2inch by12 inch floor diffusers located about 9 inches out from the outside walls Try to locate these so they blanket any large glass areas and do not interfere with your furniture placement.
As to return air I would use a single return air grille located somewhere centrally in the house. I have never understood why people mutilate their houses by trying to get return air grilles in every room . This goes back to the days of gravity heating when it was required. Now if you have a unit with a blower the air is going to get back to the unit regardless of where the return is located. If you think about it, most of the time room doors are not going to be closed, so air will circulate easily through the house back to a central return.
You should find a closet somewhere central in the house and box in at the floor with the return grille through the wall and the return duct down through the floor.
You may need some help to properly size the unit and the supply and return ducts and the RA grille.
The secret to a comfortable house is C.A.C. Continuous Air Circulation . Just use the fan on switch on the thermostat and run the blower continuously . This eliminates starting and stopping noise, is better for the motor, and keeps the air in the house mixed so you don't have hot and cold spots all over the house.
It's fascinating to see the variety of standard practices in various parts of the country.
In my area, individual returns are overwhelmingly the norm, and only the cheapest new construction has a central return.
My area is primarily a heating area, the central return folks seem to be in primarily cooling areas.
I can't think of any reason, though, that the different requirements of heating and cooling effectively would extend to central v. individual returns. (Maybe a short between the headphones, though {G})
So, I repeat - are central returns the best practice or just the cheapest we can get away with?
_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Ok, you hit the head right on the nail...it's a regional thing, probably combined with heating vs cooling.
The cost of the duct and grilles (and labor) for central returns is half that of ducted returns. Down here there are very few basements, mostly slab on grade, so you would have to run both sets of ducts throught the attic.
Do it right, or do it twice.
Well I am in the middle between you and Bob (Kansas City) so I have one of each.
I have a 2 story on slab. The first first has ducts under the slab and one pair (high low) of returns. But the first floor is all open with the exception of the of about 1/5 of the area which is where the furnaces, washer/dry and a bathroom are.
The 2nd floor is on a separate system with supply and return runs hidden in a soffit behind a support beam and part of the soffit in the kitchen and bathroom.
There are 3 bedrooms upstairs and the master has a high/low return and the other 2 have just high returns.
If you have a full basement, is there any reason not to use that for your return air source? That would also seem to benefit in that you're sucking the humidity out of there and allowing the colder air above to slowly fall down and recirculate anyways.
I imagine the main concern would be making sure you're not sucking in your HW and Gas dryer venting into the space.
With the mini-duct system we were quoted, the main drawbacks were that we really couldn't save much with any DIY installing, they wanted a huge return on the main floor cutting into the hallway, and they didn't want to put any AC in the basement (which is maybe the right thing to do, I dunno...but I was hoping to condition that space as well.)
We refinanced with the low rates this month and are pulling some money out so maybe it's time I rethink doing this. Anything new to look at in the Mini-systems over the past 2 or so years?
If you have a full basement, is there any reason not to use that for your return air source? That would also seem to benefit in that you're sucking the humidity out of there and allowing the colder air above to slowly fall down and recirculate anyways.
I was just thinking the same thing. My own house has a 6.5' ceiling(open joists) in the basement with the tin supply&return ducts run down the middle, great headknockers. I could get rid of one of the ducts and de humidify my basement in one fell swoop.
Hmmm
Mike
If anything, you'd think you could just put in a floor vent ala old gravity systems...that'd still save you the head-knocking.
We have an 8' basement ceiling and would like to finsh it. I plan on keeping the joists open, so I could easily leave the tops of the divider walls open, allowing for circulation in the basement for the intake. Again, my only fear would be concerns with the Dryer and HW venting...but there should be a solution to that, eh?
I guess the other drawback would air filtration, as you'd only really be filtering the air of the one room you have the intake. That said, you'd have that problem with any single-return system, right?
I'm thinking much the same. For all intents and purposes, my furnace could have the inlet vent right on the plenum with no ducting, as there's always airflow from all areas of the house to it.
Mike
For all intents and purposes, my furnace could have the inlet vent right on the plenum with no ducting,
The return can't be too close to the furnace, water heater and dryer flues._______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
I hear ya. I've got to check my local codes for distance specs.
Mike
Interesting dicussion on the returns. Since our house is just a basic ranch with living room on one end and MBR on the other end (total of 3 BR's in house), we could get away with one main return. But a return in th MBR or main hallway near the MBR and one in the living room would probably work better.
SJKnow a little about alot and alot about little.
As I see it there are several possible problems with this.
first you need to have free exchange of air from the upper floor(s). That means installing vents and it also means the exchange of noise if the basement is used for reckroom/home theather and the like.
And while this might work fine for heating seasion it would not work as well for cooling.
The hot air is going to stagnate at the up parts of the room and even worse on 2 story house.
And if you have floor level registers in the first floor all of the cool air will quickly "fall down" to the basement when it will build up until it reached the basement ceiling level where the return air ducts are. It will be nice for cold storgage in the basement, but hot on the first floor.
My home is 2 stories on slab with 2 separate systems. Only the 2nd floor has AC. With on insulation between the floors and an open stair well the 1st floor stays cool most of the time.
And I have 1/2 story above the 2nd floor where the garage and an entrance is. (I am no a hillside the you enter at the top which is at road level) That small entrance does not have any ductwork and being at the top is hot all of the time.
Bill, thanks for the comprehensive reply!
Vents aren't an issue if I went thattaway, so neither is noise.
It's a single story ranch with a half full basement and a converted garage/music studio. The Main level is open except for bathroom/bedroom doors which are all undercut, and seldom closed. The furnace is at the bottom of the basement steps that lead up into the kitchen, which is in the center of the house. So I'm thinking the air would just run down the stairs and into the furnace. My return ducts are already on the floor, and we have ceiling fans in most rooms, so I'm hesitant to think it would be any more uneven than it already is.
Unless it's hot out and the studio/garage door is kept open, the basement is always cool even with no AC on and the main floor is at 90. It's partially buried, and I think that has a lot to do with it. -and the cause of the humidity too!
Mike
Well it should be easy to experiment with by just disconnecting the duct work NEAR the furnace.
This might be what Bob mentioned, but I think that there is a code requirement to keep air returns so many feet away from the furance so that if there is an spillage of CO that it won't circulate it through the house.
How hard would it be to bring a single return duct up and put it high on the wall instead?
High up on the basement wall? Easy. Main floor no way.
I still have to check local codes for distance to furnace, etc.
Mike
Just becareful atht the return isn't too close to the furnace - if it is, it can depressurize the area and pull the flue gases back into the house and then evenly distribute all that CO and CO2 around the house.
There is a reason furnaces now come with a disconnect switch on the blower compartment door!_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
Thanks for the input Bob, I knew you'd be here for the safety aspect.
The furnace sits unsecluded in the basement(about 20x30) at the foot of the basement stairs from the kitchen(always open airflow), so I don't think that would be an issue. I can definitely see the potential for trouble if it was stashed away in a utility room or such...
BTW, that vent-free propane fp I put in the LR has turned into one of the best improvements I've done so far. TONS of output heat, and no CO/CO2 problems at all.
I can't believe the previous owner thought 12' of 6" flex duct and one register would supply enough heat for a 15x20 LR. Next year that room's gonna get redone and I'll be able to build a mantle, etc.
Mike
I understand the issue with heat rising and that direct return in the basement wouldn't do anything to remove that hot air, but neither would a single floor-based return, correct?
Even with the mini-duct system, I was told by the installer that they only needed one return on the main floor and that as long as I kept the first floor door to the upstairs open, everything would be fine (we live in a 1 1/2 with the upstairs being one large, usually HOT room).
My thinking would be that the best solution would have a balanced return sucking hot air from the tops of the first and second floors, but I don't see anyone really recommending that from a cost/installation complexity standpoint, so wonder if basement intake is really any different than a main, first-floor intake.
In my case, this would only be the cooling system, so I wouldn't have to worry about backdraft on the furnace...though the dryer and HW heater would still be a concern.
In my case, I was thinking of putting the blower behind our basement stairs and leaving the stair risers open after refinishing. This would pull air from the largest of the basement rooms. I agree that noise would be an issue...but nothing is noiser than the current window units we have ;o)
That's kinda my thinking, my circulation should be no worse, and I might even gain a little flow due to the lack of restriction on the intake side. I'd also gain alot of headroom in the basement.
Mike
My 12 year-old 2,450 SF house in Central NJ has a builders-quality one-zone central forced-air AC/heat system. It has one large return on the second floor, and two smaller returns on the first floor, and it just doesn't work very well. I've been getting quotes on adding a second zone AC/heat to the second floor, which is too warm in the summer and too cool in the winter. Quotes are coming in around $7 - 8,000, some higher, some lower. Most of the companies I've spoken to have said that most homes they replace or add AC units to have 1) very poor ductwork and 2) insufficient returns. According to them, the ductwork is the most important component of a AC/heating system; with great ductwork, you could put in a cheap furnace/condenser and the system would work much better than the best furnace/condenser with poorly-designed and installed ductwork. This makes sense to me. Concerning returns, if the blower is supposed to put out 1,200 CFM, but the returns only provide 800 CFM, the system won't function properly; again, makes sense.
My feeling is that it's wiser to spend a little more to get good quality equipment and installation. Get references, and go with someone with experience in your style of house.