Retrofit full heat/ac system in 60's modern
We're looking at another house renovation & rec'd great advice from the board last time we renovated.
The new project is an architecturally significant modern house (1962) in the NE--post and beam, large window walls--like the Eichler houses in CA. No attic (cathedral ceilings, original flat built-up roof w. parapets). Ballpark the house is about 3800 sf, single story, roughly in the shape of a 'T'. Windows & sliders are all single pane commercial aluminum. I have no idea about wall insulation, or whether there is any insulation in the room deck. The uphill half of the house will need a new roof (top of "T"), & could have insulation added when a new (likely membrane) roof is done.
Construction is over a vented crawl space.
Existing system is a two furnace gas hot air system delivered almost exclusively through floor registers. The smaller furnace feeds the master bedroom/office (top of the 'T'); larger furnace feeds the large open LR/DR/Kitchen as well as the kids' bedrooms. I suspect the zoning was design driven--it looks as if the crawl spaces are isolated by foundation walls. Uninsulated duct work is all through an uninsulated crawl space. Currently the house has no air conditioning system. The existing main furnace is on its last legs (dreaded blower bearing knock by the sound of it...)
We would like to bring the house HVAC systems up to modern standards, add A/C while also generally improve the energy consumption footprint.
I'm a big fan of underfloor water systems, but 2 problems--existing wide plank hardwood floors (that may be salvageable), & you would create a bigger problem as to how to add A/C.
So assuming that you try to work with what's there....
1. How hard would it be (or how efficient is it) to add air conditioning to an existing system as described? (eg no ceiling drops & very difficult to install in roof slab--also you don't want to detract from design)
2. Should the underfloor joists be insulated?
[There are also moisture problems in the house--first contractor has recommended a vapor barrier be installed and a "rat slab" be poured. (I'm inclined to deal with perimeter drainage first...)]
3. Should/can the duct work have insulation retrofitted? Is this wildly expensive? (most of the crawl space is 4' or less...)
Other Improvements may include:
-Window replacement (for all except the clerestory windows that "knife" into the under-roof deck.
Where to begin? Or what is the recommended sequencing to get my arms around the problems???
Last edited by paredown; 01-19-2008 at 06:25 PM.
Load calc ,with various options,better windows,insulation ,etc.,each will effect the size system that will be needed.
Once you decide on those factors,you'll have the load of the finished product.
Then Manual S to select the equipment size,and Manual D to size the ducts,reuse and insulate what you can.May need a different style supply grile,due to adding cooling.
Where are the supplies located?
We did a similar style home retro,guys dubbed it the "glass house" job,real challange ,but fun to see it all come together!
Your ductwork could be lined.
Good chance its too small for A/C.
Follow dashes advise.
Wow, you guys must have already had your morning coffee! Thanks for the quick responses!
I see "Manual S" and "Manual D" mentioned all over the board, & I didn't stumble across a quick definition...
Originally Posted by dash
I'm assuming "supplies" would be what we used to call "returns"? The main one (if I'm reading it correctly) is a large floor one in the cathedral portion of the house. Not sure about the smaller unit.
"Lining" ducts would be the insertion of something inside the existing sheet metal?
Manuals J,S and D ,are from www.acca.org and are the industry standard to deterime the load,select the eqipment and size the ducts.
Lining the ducts is insulation on the inside as opposed to the outside.
Supplies are the ducts and grilles that deliver the air to the space/rooms,location and type grille is critical to even temperatures in each room.
Pictures would help.
Sorry, got it back to front--all I have pictures of are the floor vents--I didn't have my camera when I was down in the crawl space. FWIW, here are a couple of shots first is one of the floor vents, beside one entry door; the second is the LR area--and what I think is main return for that area, just in front of the center white partition.
Partitions are just to define space...
A couple more shots: the first is looking at the window wall; the second is in one of the far kid bedrooms (bottom of "t")
Sorry for the thread dredge, but we are (finally) in a position to do something about the heating in this house.
I have had an installer do a heat load calc., and he has given a quote that involves a furnace upgrade for one furnace, provision for A/C when we can afford it. He has also suggested moving the main return to a position over the furnace room door which would allow the elimination of a badly-done boxed plenum in the crawl space, as well as eliminating at least one other return (on the hall wall). In short, he seems to know his business, and spent enough time to think through the problems in this house.
1. With a HE furnace, how do you get the combustion air to the furnace, if the furnace room is marooned in the center of the structure? (What we had in a previous house was PVC taken straight to an outside wall; in this case you could go down below the floor and take it out at foundation level or?) I was unclear what he was planning & wanted to know more since I am also trying to deal with roof issues. I'm assuming exhaust could be taken out through a lined chimney or dedicated roof vent?
2. One thing he commented on was the way in which the house was zoned between the two furnaces. The house is a very long single level with a 'great room' as the center. Both furnaces had their main returns in that great room (although he was going to relocate that for furnace #1), but the supplies in the great room are split based on proximity to the respective furnace. This is a high-ceilinged room with lots of single pane glass.
His suggestion was we might want to consider splitting the supplies so that Furnace #1 would have all the supplies on the east side while Furnace #2 had the west side. I think he said that if the thermostats were put in the correct locations, then if you have say thermal gain from one side of the house, you would then call on the furnace that would do the most good--the one on the cold side.
Does this seem worth doing (it would involve some duct work in the crawl space....
Would need to see the house to give any good opinion.
I did a Frank Lloyd Wright style years ago, only underground (underslab) system I ever did. Upstairs had slot diffusers paralleling the glass curtain walls. pretty cool house.
Since it was new I was able to run the four pvc flues for the furnaces behind the rock veneer on the central fireplace as they built it, and was concealed under the chimney cap on the roof.
also, some manufacturers allow the flue and intake to run through the crawls IF certain conditions are met, so the crawl wall could be a location for the venting w/o penetrating the roof. Warning- don't put under window- you'll see a cloud of steam whenever the furnace runs in winter (made the FLW house tricky with all those window walls).
4' is plenty of space to work in the crawl. I do like sealed crawls- since they're humidity controlled, you don't need to wrap the duct to prevent sweating, and there's no heat loss from the ducts to outdoors. Insulating the walls could result in less heat loss from house than if the floors and ducts were insulated.
questions asked, answers received, ignorance abated
Thanks for those suggestions--I have been working on the idea that I will seal the crawl once I can deal with it. Slot diffusers would be nice under the windows--this house has only standard registers and they are not so well-placed.
Unfortunately, a direct run from the furnace room to either outside wall would in fact end up under a window, so the steam would be a problem.
I'll talk with my furnace guy to see what his suggestions are.