Improve Heat Pump Efficiency - Attic Air Handler and Duct

You need another return. Especially if the incoming air is coming out of the register right by the door.

The air comes in and gets sucked right back out.

Just a guess.

I think this may be necessary too. Can somebody tell me how much attention to pay to the balance between air in and air out? based on calculations you see in other posts here, I've got approx 765 cfm coming in and a return rated for 1000cfm. The 2.5 ton system is rated for 100. cfm. Does this suggest that there is "room" to add more to the supply side too?

I don't live in the deep south, but far enough. And I have lived in southern Georgia.

I don't know why it is exactly, but I hear this all the time from people. All I can tell you, is that I've run into a lot of people with these upper rooms, that end up, after trying everything else, with a window unit to supplement the regular AC.

It's, (I think), the most efficient way. No ducts, cold air, no real work.........come late October, you pop it out and store it until May.

In the end this may be just what needs to happen. Before that I'm gonna make sure that everything else is in order. I don't think it is. I'm also curious what the net effect of this would be on cooling costs. I imagine that the central system would run less but would the addition of the window unit equal a net reduction or increase in expense?

Typically what I see is that they tend to install central units that are too small to serve these upper spaces. I'm not an AC guy, but it's as if they size the proper units for the square footage, but don't take into account the fact that heat rises. This is a very common complaint around here.

I can't make a guarantee, but I would imagine that since your current unit is totally overworked, and probably never shuts off when it's hot, that you would experience a decrease in expense.

Go figure. You'd think that A/C folks would want to sell equipment of larger capacity. The last home I owned I got to select the equipment and DID go with an upstairs unit slightly larger than warranted, at least based on sq footage. And there was always enough air.

I'll try all the remedies mentioned here and elsewhere to improve the system's performance but in the end if it's not enough it's not enough. The addition of a window unit may make all the difference.

Thanks for thinking about it with me.

Kramarat has good thoughts. My first house was an uninsulated summer home which we lived in year-round. After one year, I insulated the underside of the roof (leaving an air space open to the outside) with 4 in fiberglass behind sheetrock, and I caulked all, that is , ALL of the openings in the exterior - foundation, shingles, windows, chimneys. No other insulation. The house became pleasant and the attic became usable winter and summer. Heating cost went down over 50%.

I do not have numbers, but I think the flex hose has higher resistance than metal box ducting. K's focus on cooling the attic is very important - someone with air moving knowledge and a beer or two could help a lot.

That's a substantial improvement with minimal cost, lots of effort, but minimal cost. Any particular reason to use sheetrock other than the ease of installation and it's R-value? Do you think you would have experienced similar gains by hanging the sheetrock by another method, something easier like wire mesh? Your focus on caulking the entire house, everything top to bottom, is another good suggestion. We've been "plugging holes" since day one but another all out effort would likely yield good results.

Forgive me, I may not have been clear. This is a split system. The air handler and all duct are located in the attic space. The attic has lots of open space (1400sq ft with 10 -12 ft ceiling height) but lacks adequate ventilation. There are two gable vents approximately 2' x 4' each and maybe 5 small rectangular soffit vents (not at home right now to count). The condensor is outdoors in a well shaded area. Increasing ventilation to the attic sounds like a first order task. I would think that increasing the area of the vents, adding fan(s), and providing some type of radiant barrier could make substantial gains. The idea that someone has posted suggesting that I hang something, fiberglass insulation or foam sheets, to the roof rafters sounds intreaguing. Any thoughts?

I get it.....I misunderstood.

I'm not sure about insulating directly under the roof space. I use one of these in my attic. It's a thermostatically controlled vent fan. They are fairly inexpensive and they work great for circulating air in the attic. They will also prolong the life of your roof. We get days over 100°F here. This fan runs a lot........the electrical use is negligible.

Exactly!

The 3 should have been up and the 2.5 down. In moderate climates such as Sacramento most of the time we can get away with 20% over size up and run just the fan down. The cool air has a tendency to cascade to the lower level.

Deep South has the humidity issue so the original system should have been sized at 600 cfm divided by the total home sq ft due to the air density problems with humidity. The throw at the wall sizing for most houses is (home sq ft/400) that will give you required tonnage with fenestration factored into the number.

The duct size can be increased but in the end the system only has so much capacity.

Another reason 2.5 tons should be adequate upstairs is that I've misstated the upstairs sq footage. It's actually 1400 rather than 1600. Ventilation is something I will be working to improve.

WOW! This is great help.

I don't plan on installing new windows. The historic district doesn't like them and they would be incredibly expensive.

The back of the house is well shaded and you are right it makes a huge difference. We've added some trees in the front that in coming years will help.

The radiant barrier might be quite useful. Basically you are talking about lining the roof rafters with some type of metal backed insulator like, for example, foam sheets. Correct?? Who sells this?

The roof is dark and the driveway made of pebbles. I'm stuck with the roof for, hopefully, another 15+ years.

And the laundry room idea intreagues me. Yes, laundry is in the house, conditioned space. If I understand correctly, you are suggesting that I install some type of piping on the suction side so that air is pulled from the attic rather than conditioned living space. Brillant! Why didn't I think of that? What do you mean by "just use a filter over the top"? And will metal duct tape that secures a nicely fitted metal duct pipe to the intake of the dryer accomplish this?

I'm constantly mindful of heat sources like computers, lights, TV etc and we turn them off whenever not in use. We've shifted to all low wattage high efficiency bulbs and during the hot months rarely use the stove and never the oven. As you say, it's a nice excuse to grill.

I think more attic vents, a solar roof fan, and the dehumidifier would also make substantial gains.

The air handler is unobstructed and clean. The condensor is also clean and well shaded. Last night when I looked over the entire duct system in the attic one more time, I became increasingly aware that two of the ducts supplying the side of the house that doesn't receive adequate air flow (that's one of my main theories re the problem) have several turns in them. I plan to reroute these so that the runs are as straight as possible and then wrap the flex duct with another layer of metal backed fiberglass insulation. Another person who has posted a response also suggests that there is not enough air flow AND that I need another return on that side of the house. I think I'll go with most all of these suggestions. The bottom line is that I want the system to cool properly at the least cost.

Thanks for all of your help.

Straight supply runs are important. So is keeping the air in the room long enough to work. The return must be as far as practical from the inlet.

Interestingly the side of the upstairs that is problematic is furthest from the one 20 x 25 ceiling mounted return that serves this system. The return is located at one end of the upstairs hall and the bedrooms and bath that are closest to the return have doors that open to this hall. They are well cooled. The problematic side has only one door and this serves as the only route for air returning from that side. This door is located at the opposite end of the hall relative to the return grille. This door is at the front of the house while the return is at the back of the house. So the route that air travels to the return duct from the problematice side of the house is longer and much less direct that that traveled by air from the other side of the house. I hope this makes some sense. In the end I do think that creating a more direct route from the problematic side of the house to the return will improve performance. This could be accomplished by adding another return altogether or by opeing wall space for air to be pulled along a path other than through the door at the opposite end of the hallway.

The metal backed foam sheets referred to here is a quick and good way to cool the attic (available nearly everywhere, e.g. Home Depot, Lowes, etc). It also allows you an opportunity to control the leakage through the hot roof into the house. In a house that has not been sealed, leakage is a major source of loss, both hot and cold. You do need to make sure that there is a path for air movement into the space behind the foam sheets and out from under the foam sheets. Usually this is from eave vents at the bottom of the roof edge and out at the top in a ridge vent. the ridge vent can be added to a roof with no ridge vent by removing the cap shingles, cutting the roofing and roof wood back to make a slot for the air to escape, adding a roof vent and shingling over the roof vent. In a renovated older home you can reasonably expect that it was not originally there, but it may have been added in the renovation. If you do not want to add a ridge vent, you can (see pictures at #21) close in the triangular space at the top of the attic created by the horizontal bracing and tie that space into the vents in the end walls. By the way, you said " The condensor is also clean and well shaded". Does this mean you have a split system? If so, then a powered vent fan can help a lot. The potential problem with a powered vent fan (blowing out) is that it will put negative pressure inside your home and pull the hot outside air into your living space. Older homes often have the interior walls open into the attic or at least not sealed, so that suction in the attic creates suction throughout. Sealing the air leakage is the first thing you need to do. It is more important than insulation (see my earlier post). Powered HVAC systems often use "high pressure drop/small ducting"design to reduce the installation costs, making the power cost higher. This creates a situation where unbalanced or inadequate sizing will promote hot air mixing in where it is not wanted, overcoming normal air flow with the large pressure differential of the powered system.

Glad to be of assistance.

The most simple radiant barrier for existing structures, imho, are the rolls of what looks like shipping bubble wrap that has be aluminized. Home depot and lowes carry this. The installation is staightforward. You must have ridge vents (or alternate for removing heated air in the channels created between rafters) or the heat buildup will cook/damage your roof.

BTW, you don't have to put on a new roof to enjoy the benefits of a lighter color. Surface treatments are available for most types....and the further out you reject the heat, the more effective. If all the neighbors have to gossip about you for is seeing you whitewash your roof, you probably aren't having enough fun. :-)

The only trickey thing with creating a non-AC intake path for your drier is making sure it does not present a hole in the AC envelope. Two approaches are: modify the rear of your drier to directly attach the suction to the newly created intake vent or seal the laundry room from the ac envelope and attach something to the door to close it consistenty. My preference is to attach the new line to the drier. Each drier will be different, but essentially you will be taping over some places the drier normally pulls air in, and creating a larger new intake that attaches to the line. Aviation shears and a kit normally intended to create a drier exhaust thru-wall box are helpful.

Concerning the placement of the return upstairs. You should consider running individual return lines (in the attic and connected to the room through registers just like the supply lines) to the problem rooms. This will allow you to 'tune' the system with flow regulating orifaces (cut out of cardboard perhaps) in the supplemental individual return lines.

One more thing to consider is making your air conditioners more efficient by supplementing your current condensers with additional heat transfer to a hot water preheater tank, or something like a pool or pond.

There are systems and installers for this type of system, or if you have good access to a good length of the refrigerant lines to and from the condenser, coiling soft copper around the refrigerant lines (or even just run a couple parallel, some potting compound or heat conducting adhesive would help) and insulating really well, with a small recirculating pump (pumping counter flow) set to pump when the unit turns on or on a temperature switch on the refridgerant line, would be a fun weekend project.

You might end up running your hot water preheater recirc line other places as well, like close to refridgerator coils, on the drier exhaust, or around the drains from the shower and dish washer.

Have fun.

That solar fan should have been your #1 ... simple to do and IMO has the biggest immediate impact.

Addressing #4 That is attention to detail!

I used the void in the interior wall that 90's to the outside wall. I removed the top 2x4 portion ... cut a hole at the bottom by the dryer and covered it with an AC filter. The room has an exterior and interior door, so I weather striped the interior door as well to seal it as good as possible. My intention was to get the hot air to improve efficiency. Not once did it dawn on me that it would also prevent the suction of AC'd air from inside ... now I have more ammo to tell my wife to close the laundry room door! She says she can't hear the buzzer go off when it is done. Imagine if it were outside! lol :o)

Next project ... heat exchanger to recover the heat in the winter. :o) any ideas?

From an air-conditioning standpoint, the upper story would present a substantially higher load than the lower. I'm not sure, but it might even represent the larger heating load in the winter as well.

Your air flow sounds too low, but I would need to do some further checking to be sure. I'm not sure how much greater air flow the present ducting would accommodate.

I'll try to look a little further.

Thanks Tornado. I imagine the air flow to be too low myself. I calculate it this way but please let me know if I'm off base.

3 8" flexduct supply running a total of approx 70 feet = 480 cfm

4 5" flexduct supply running a total of approx 100 feet = 240 cfm

1 4" flexduct supply running a total of approx 20 feet = 45 cfm

The return is a 15" flexduct running approx 10 feet

This suggests to me that the system can handle moving more air.

One thought I have is to increase one of the 8" supply lines and two of the 5" supply lines (these feed the side of the house I'm having trouble with) to a 9 or even 10" and 6", respectively, flexduct. This would add a net of 115 more cfm (using 9") or 200 more cfm (using 10"). I could also cut a hole in the wall between the two sides of the house, cover both sides with attractive grills, and thus there would be no increase on the return side but air would flow more directly/effectively from the problem side to the return.

However, first I plan to reroute these same ducts so that they run in a more straight line and then cover every foot of flexduct (all the supplies and the return) with another layer of metal backed fiberglass insulation. If this doesn't effect adequate change I will more to increase the size of the ducts.

Any thoughts? And thanks again in advance for sharing your wisdom.

I would do a flow study. Get incense sticks and first start with a person in each room, and let the smoke go into the intake. See how quickly each room gets smoke, and how quickly the smoke leaves the room.

`Like mentioned, if the smoke immediately leaves the room, it won't get cool.

Thanks Mike,

that's a great idea and easy way to get a handle on how much air is actually flowing... without the fancy gadgets anyway. Sounds like to first next step. I just posted several responses to other comments so if you have any other thoughts please let me know.

You mentioned lots of insulation in the ceiling - very good, but what about the walls?

Are they insulated also particularly of your sun facing side?

Bill

Yes the walls are insulated with paperbacked fiberglass. The studs are 2 x 4 rather than 2 x 6 so the insulation is minimal. On the ground floor, the entire crawlspace is insulated. There are also lots of very large and very old windows around the entire house. Does anyone have experience with "window covers" like "film products" folks are referring to in other replies?

http://solutions.3m.com/wps/portal/3M/en_US/Window_Film/Solutions/Markets-Products/Residential/Sun_Control_Window_Films/Prestige_Series/

The stuff works as advertised. You cut to slightly larger size than window and apply to the wet glass. You squeegee out the water & bubbles between the film and the glass. It is the same stuff that is used in after market tinting for car windows.

Low E coatings on the inside help reflect heat back into the room ... so if you live in say ... New Orleans ... don't get those :o)

Copy and paste the above link ... that is the film you want.

I searched 'solar film'

a typical hit <http://www.solargard.com.au/Commercial/Products_Solar>

Most hits on the first page were here in Australia, I didn't look at subsequent pages, and I don't know the commercial names/descriptions used in the States.

Regards

Bill

This week I just got back from installing film window covers for a home. The film was the semi-transparent reflective roll sheeting sold by big store. Width: 36", length 15'. One roll covered about six medium-sized windows. The owner provided installation kits, which included hand spritzer with detergent solution, hard plastic wiper, slicer to trim the plastic to the window, and lint free "rag". It used about one install kit per roll. A squeegee was recommended. Simple description of installation -( I was working alone, though a helper was recommended.)

Clean window thoroughly.

Cut the sheet a little bigger (about 1") than the window. Keep one manufactured edge uncut (and thus straight).

Start to separate the clear plastic cover from the adhesive backed reflective sheet at one corner, then put something between them to make it easy to separate them completely later.

Now spray the window and both sides of the plastic with the solution.

Pull the two sheets of plastic apart, spraying more solution on the separating sides of plastic, keeping them wet.

Now line up one edge of the window with the uncut, manufactured edge of the plastic sheet and using the squeegee, press the plastic to the glass, putting the sticky side against the glass.

Trim the edges of the plastic and firmly wipe the liquid out from between the plastic and the glass.

Allow to dry. Keeping things clean reduces the imperfections in the appearance.

More complete directions are included in each roll. The incoming heat from the sun was reduced a lot and the owner was happy. I haven't done a window yet that was more than 3' wide, though I will. This material is also available in a deeper mirror which makes it difficult to see in. I do not think the application kit was absolutely needed, but it was easier, I'm sure. This was the main entrance (over two stories) with its own heating/cooling system so the architect anticipated the temperature swings needed to be dealt with, though the added noise was undesirable, and thus not used much.

"I don't plan on installing new windows. The historic district doesn't like them and they would be incredibly expensive."

An inexpensive method of improving the efficiency of the existing windows would be to add insulation. This can be accomplished in two methods:

1. Add movable shutters to the outside of the house and shut especially when the sun is shining on them. Even if the shutters add minimal R-value at least they deflect radiant heat. Older houses frequently have movable shutters so should not detract from the historic look.

2. Cut removable foamboard covers for the inside of the windows. Foamboard with a foil backing is especially great on the east and west windows. If the wife balks at the idea you can close the curtains to hide, or glue matching cloth to the foamboard to be more visually pleasing. Carefully cut the foamboard to make a tight wedge into the inside window casing and will stay in place by friction. When removed they can be stowed under a bed or couch.

Two ideas:

My brother's house has ordinary pink roll insulation installed between the roof rafters, that is, directly against the underside of the roof. I think the builder used spray adhesive. And his attic is barely warm in a Texas summer. My attic gets 150F or more. Gotta make a difference.

You can get fans that attach to a register to increase the air flow to a particular room or area. Cheaper and easier than replacing ducts, and you can experiment to get just the flow and temp you want.

If you change out as much of the flex duct with solid round you will get a major boost in airflow- flex pressure drop is over 10 times higher than same size solid pipe.

While changing out the runs, install at least one size larger solid pipe and add a concentric reducer at the connection to the flex for the last 5 feet or so going to the outlets= that will cut pressure drop by about 50% more.

If the ceiling supply outlets are either round or rectangular diffusers, change them into curved blade registers with the throw toward the exterior walls. The circulation will still maintain overall room comfort and the throw will be directed away from any return air inlets to minimize any "lost" cooling effect.

I have been applying our Energy Star Cool Roof coating to rooftop AC units and exposed ducts for 25 years. The least I have ever dropped the air temperature coming into a building is 5 degrees, the most is 25 degrees.

Our distributor in Texas has been spraying attic AC units, plenums and metal / FLEX ducts for around 6 years. Doing that normally drops the entire electric bill by around 25% for an average 1,300 to 1,500 sq ft house.

If you bury flex duct in blown in insulation, the radiant heat from above is going to heat the insulation. Now you have heat transfer by cunduction from that insulation touching the flex duct.

Our coating is not just a radiant barrier, it is an extremely good conductive heat barrier as well.

Our URL is listed on my profile.

What part of the deep South are you in?

Hal

I don't live in the south but their is cool available from underground.

A plastic perforated tile 5 or 6 feet underground can be used to draw in cool but moist air into the attic creating a barrier between the heat and your house.

The 100+ temps in the attic can be replaced with 55 degree air from the ground making quite a difference in the cooling load.

Norm

There is a plastic film that you can add to the inside of your window glass that significantly reduces heat absorption.

Once installed it is all but invisible, it adds a slight tint to the windows.

Lucky for you I'm an HVAC contractor. Any chance you can provide a diagram with duct sizes and LENGTHS? Air doesn't like travelling through 4 inch ducts very far. You could install a bigger return, this will also help reduce air noise. Insulating your ductwork in the non conditioned space was a great move. Without seeing your layout I can give you one tip. As the air leaves the blower it fills a plenum with air. That plenum is where all your ductwork is hooked up. The duct that is directly INLINE with that airflow should be where you tap into the duct you want to have the most air. So if the unit was blowing air straight up into the plenum you'd want that duct hooked into the top of the plenum, rather than the sides. You can also (after you get your measurements) go online and get a "ductulator". This will tell you what sizes and lengths of duct to use. Your return is also crucial. Again, I need a diagram. I'm concerned that the air you're drawing in is just hot air from the lower floor. Can you close off the two levels? If you can't you might want to look into install returns into the largest upstairs areas that can be separated from the lower floor. Get me more info and I'll help dial you in.

I've been building homes on SW Florida for 40 years now.

By code, ALL your bedrooms should have had a small return air duct going back to the air handler. This is because most people sleep with their bedroom door closed and it restricts air flow. If they don't have one, add an 8" return duct to each bedroom by connecting to the 15" return air duct. You may have to reduce the size of the opening in the hallway return by cutting a piece of aluminum to fit with an 8" hole in it after you add the smaller returns.

If your AC guy had sized everything correctly the bigger rooms farthest from the air handler would have the largest ducts. Flex duct is very effecient and the one inch thick insulation they are made of looses very little heat and gains very little heat when in the cooling mode. That's not your problem upstairs.

They placed the big return air in the upstairs hallway because that is where the 'warm' air is rising from the first floor probably ends up. It is pretty much useless at night with all the bedroom doors shut and no returns in them.

Energy wise, you windows are your biggest loss. They should have been a priority and could have been matched exactly to the original look with thermal paned glass but admittedly at a pretty high cost, relative to payback time if you don't add in 'comfort level' to the equation.

A Low-E film is your best investment at this point. It will block the sunlight carrying heat into the house. Also, storm windows like they use up north in the winter would help but you didn't say what style windows you have.

You didn't say if you were able to insulate the outside walls of the house.

Insulate the gable walls in the attic with some foil back sheet foam, facing the foil to the outside. A power vent on the cool end gable pulling cooler air into the attic and forcing it out the opposite gable will help if the attic temperatures exceed the outside temperatures on hotter days by more than 10 degrees.

White metal roofing reflects sunlight the best. If you re-do the roof, see if the historical people will approve it. Most of them are from up North, have only lived in Florida less than ten years, and have no real idea what the neighborhood looked like 50 years ago. Those of us that have lived here for 50 years know that change is part of Florida's history.

"Deep south". Is that Bournemouth?

A major element of heat gain is radiant gain from the roof-"shining" down on all below.

Conductive insulation has nothing to do with radiant gain, except to slow down its transfer.

Add a radiant barrier to the underside of the roof/the rafters/or the bottom surface of top chord of trusses. fitting around web members need not be exact, for this is putting your conductive insulation in "infra-red shade", it is not a vapor barrier. Some is good, more is better (like shade on a summer day); if you cant get to the very edges...well OK.

Shiny side down, is counterintuitive, but prevents gradual declination of radiant effectiveness by dust contamination. (%reflective + % emissive =100%) ..Doesn't make any difference.

All this is about decreasing loads. I go to www.innovativeinsulation.com; they ship UPS, fast, and it's an energy credit still. Install fast, before your attic is inaccessible until fall.

In addition to changing the flex 5" to Solid 6"(or larger if it runs the farthest from the return). I would add a solar powered fan over the warm side. It may just be that it is warmer on that side due to it's southern orientation (sunny-side) ... But I could not discern that from your OP.

I have the one from these guys in my 2nd floor attic ... http://www.sunrisesolar.net/

And put 2 from these guys on my parents ranch style house ... http://www.atticbreeze.net/products.htm

They made a profound difference. Passive ventilation is better than none ... but active is an order of magnitude better. So I'd either go with the gable fan ... or go with the solar fan I installed.

And if you have a ridge vent, nix it if you go active ventilation. I smoke tested mine and found it drew a substantial amount from outside the ridge ... so I plugged it up about 6 ft on either side until it was too blame hot to do any more, then over the winter I just got rid of it totally to save the heat in the winter.

Oh ... and don't forget solar (blocking) window film ... another drastic improvement. Allow me to joke, but aluminum foil works incredibly well. I have a whole home solar system and am not above using it. I made a frame to insert into the window and 'display it' on some of the merciless hot days. Especially on those days I like to sleep in ... warns the neighbors not to come calling and keeps the bedroom cooler & darker. :0)

BTW ... I have a window unit also :o) ... at night and in the late spring & fall it is the only thing you have to use for the whole house & it runs off of generator power ... (think hurricanes in the deep south) Still, I'd have one just to stand in front of after cutting the grass mid summer.

Good luck with the endeavor.

If you want comfort, start with the windows. Double pane or triple pane argon filled.

As you stated the house was gutted and insulated, plus all the good work you did in the attic, than your greatest heat gain is through the existing windows.

I talk from experience. I was going to up-size my AC, as it could not keep up with the heat load. After changing my windows and insulating the attic, there was no need. Not to mention the massive change for the better in comfort, along with the energy savings.

As for the upstairs unit and the down stairs unit they are reversed. The return air duct should be central of the second floor. If not than a second one will be required. The greatest mistake I have seen in installations is that the contractor does not pay attention to the return air. It is either misplaced or undersized.

Since you already stated that you cannot (local "historic" requirements) change out your windows, you can at least install indoor storms. If possible to buy them that way, get 'Hi-E" coating on them (reflects IR radiation toward "warm" source). If not available, you should be able to buy film with same effect.

It is clear, so no detraction due to shading film and should meet "historic" standards.

If you want to be able to open windows on "nice" days, you can use magnetic tape to secure windows to your existing window frames so you can easily remove to operate windows and then replace for comfort during winter and hot weather.

I missed the historical requirements. Can not new windows be manufactured to be physically identical to the existing?

If not, than your suggestions are the best he could do.

"New" windows to match existing might be possible- at a very premium price- because they would need wood sashes matching current style AND be double-hung- both of which are not available from many suppliers.

Is it not possible to have vinyl windows made to look like wood and double hung, and archaically correct in order to meet requirements? We do that here.

Yes it does cost. It comes down to comfort and energy savings verses the existing windows.

Unless your house in on the National Historic Register list the local Historical Committee can only stipulate how the house looks from the street.

You can get excellent double hung, Low-E, double pane, Argon filled windows from Lowe's or Home Depot for less than $400 each for a 36" x 64" size. From the street you can't tell the difference.

For $600 each you can get them in aluminum powder coated in custom colors with external grids that are nearly impossible to tell apart from the original wood windows, even up close.

They are very easy to install since you custom size them to the exact rough opening the original windows were installed into.

The pay back on these is when you sell the house but the energy savings should be nearly 20% of your electric bill from day 1.