Replies

1. 
   [email protected] | Jan 26, 2011 03:23pm | #1

   How much extra space do you have.

   The mechanical room, needs to have enough space to install and service the unit.  Typically the unit is sized first, and then the framing done to the manufacturuers minimum, so that you don't "waste" space. 

1. 
   DoRight | Jan 27, 2011 12:51pm | #2

   Joist lay-out

   I am not worried about the size of the utility room itself.  I am thinking about the joist lay-out.  In addition to working on the design of this home I intend to do most of the work myself.  Therefore, I may get to the framing before I get to selecting an HVAC guy.  So I was trying to figure out how to lay-out the floor joists so as to be adaptible to different sized plenums (spelling?).  I was thinking of just doubling up the joist on one side and then double up the joist other from there at 32 inches, use a double header (not sure you would call it that) between them so as to hang a joist between the doubled up joist wherever needed at the time the furnace is selected.

   See any problems?

1. 
   [email protected] | Jan 27, 2011 05:19pm | #3

   Typically 16-inch OC

   16-inch OC shold wokr for most systems, if they have enough length to work with. 

1. 
   DoRight | Jan 30, 2011 04:57pm | #5

   joist spacing

   16 OC?  Are you suggesting that they will just cut one out or would they split a plenum around a joist if necessary?  I am thinking that many furnaces have a large box plenum (24ish x 24ish y 24ish) attached to teh underside of teh furnace throught the floor (either a cold air return or the downdraft (not sure that is the term) for the hot air.  16 oc seems tight unless they cut one out.

2. 
   Clewless1 | Jan 29, 2011 09:12am | #4

   Are you down drafting to ducts in the crawl? I'd think that a standard 24" oc joist spacing would be enough for many residential systems.

   You should at least scope out your furnace system a little before framing. If you know your furnace size (btuh), you could pick a sample (e.g. Carrier) and check the dimensions of the supply plenum. At least having a general understanding of the furnace size (physical and thermal) and the type of configuration (e.g. downdraft) is an important part of the design process. You should even do a preliminary layout of the ducts and register locations. A little planning ahead may save you great pains down the road.

   You are at the design stage ... you should design ... and that is more than ... framing and house volume/style. Start thinking electrical, plumbing, etc. Don't sell your design short by overlooking some aspect of the mech/elect in the process.

1. 
   DanH | Jan 30, 2011 06:23pm | #6

   Yeah, I did some poking around on the net, and found that manufacturers are remarkably non-forthcoming WRT the dimensions of their furnaces.  Did find one reference that indicated dimensions ranging from 16" to 25" for the plenum width, depending on unit size, and looking at our Carrier manual found roughly the same.

   So, for a counterflow unit one definitely needs to plan ahead on the joist spacing, or else plan on placing a plenum box below the unit to split it up before it goes through the joists.

2. 
   DoRight | Jan 31, 2011 12:28pm | #8

   Yes, Crawlspace and design

   Thanks for your comments.  Yes, I am working out all kinds of preliminary design elemetns and in great detail, this is why I am asking about furnance installation.  I have also been looking at how the hot and cold heating trunks must run as, as you know, drainlines can not go up and down, over and under such ducts.  I appreciated the heads up on the need for a complete design, not just a fun napkin design. 

1. 
   Clewless1 | Feb 01, 2011 08:15pm | #12

   I'd target a couple of name brands and look for a likely model to gain a comort level that the furnace you might choose will be doable w/ your framing. E.G. ... check out some Carrier or York down draft furnaces, get the specs, do some good preliminary layouts to know where the trunks will go and the branches and registers will go. You'll probably find that there won't be issues assuming you have joists 24" oc. If 19.2"oc, you might need to take care, but may still be plenty adequate. 16"oc. ... may be tight, but it all depends on your house/furnace size, too. Extra big houses will require large furnaces or use two.

   You should have a solid starting plan w/ the understanding that there will be some degree of "Plan B" that you'll have to consider. Think of your drain lines and how they might impact the ducts. Having thought about it consciously helps you deal with the stuff later when you go to install.

   Good luck.

3. 
   Tim | Jan 31, 2011 11:03am | #7

   Furnaces

   come in a standard depth of 28" and four standard widths, A- 14.5", B - 17.5", C - 21.5" and D - 24.5". Top and bottom outlets are 19-5/8" X width -3/4", bottom inlets are 23.5" x width-1.5" . (Those who have to look this up on the internet to form their "expert" advice don't know these basic facts)

   IF you going to have a cased AC coil on top of or beneath the unit, the dimension in and out should be close to the same. For a downflow unit, with a supply plenum in the crawl space, I would size the plenum to fit between the joist and otherwise long enough to properly handle the air conditioning required air flow.

   The only real consideration is that the opening be more or less centered beneath where you plan to place the furnace. A good sheet metal installer will be able to accomodate any framing you come up with. I recommend working with the installer, and that installer should not be you.

1. 
   DoRight | Jan 31, 2011 12:41pm | #9

   Thanks Tim

   No I don't plan to install the furnace.  I may consider doing the duct installation, but not sure.

   It would be a great idea to as you say work with the installer, however, I fear they may not be to interested in talking to me as the furnace installation is still some way or a long way down the road.  This is of course very short sighted on their part as I can tell you those willing to talk to me now are those getting business in the future.  It is exactly like teh guy I was talking to about gas fireplaces.  I was asking about chimeny chases, venting, standoffs, etc.. I did not even tell the guy I would be the builder.  For all he knew I had a buiilder and was just trying to figure out what I wanted him to install.  He was very short, did not answer many questions, and then I felt like he about throw me out of the store, when he said when you build it we will figure it out.  Well I know one thing, I will not be buying anything from that store.

   As for the furnace, my basis for the question was that I figured all furnace sizes were different and that not only wold I need to talk to a furnace installer, but more or less get several bids and make a selection NOW.  So I was thinking I might be able to hedge my bets by doing some kind of general, somewhat flexible framing job to accomodate multiple furnace options.  If that is not the case, then plan B.

1. 
   Tim | Jan 31, 2011 04:25pm | #10

   I understand

   to a degree, the attitude of the salesman that was uninterested in being a source of information. That doesn't make it right. Its not necessarily wrong either.

   I have been involved with companies that sold commercial HVAC equipment, as well as residential equipment. My focus was, and is, primarily commercial HVAC. There were many times that I spent quite a bit of time and effort with a homeowner/small time builder and/or DIY. They can be a huge time killer, and the business is sales. Remember that, when you feel you might be treated brusuely. Time is money and you're taking theirs.

   On the other hand, be honest and forthright. Tell the salesman what you're doing. "Hey, I'm bulding a house and plan to use one of these fireplaces. What do I need to accomodate it?" If the guy is sharp, he'll know immediately and for him to get you the necessary details is an effort of seconds or a minute or two, at most.

   I, in addition to my day job as an application specialist at the premier manufacturer of commercial HVAC equipment in the US, have a real estate investment business dealing with samll multifamily properties and single family homes. My business to a wholesaler is a drop in the bucket compared to that of an established contractor. So, I tell them, when I approach someone for pricing, literature, information et al., "Hey, I buy, sell and lease small apartments and houses. I'm not going to spend a million dollars this year at your business. I WILL be spending $XX,000 or so and I need......" Either they work with me or they don't.

   Do they want to be the guy that I keep coming back to, time and time again because they treated me like a valuable custiomer, or the guy that I never go back to again, and encourage everyone on I know to go elsewhere because they treated me like dirt? Some don't care, but they usually fail. You cannot have a successful sales business or career if you don't take of everybody.

   For your furnace, there are a few basic questions to be answered to narrow the selection down. 1) location, square footage and construction of the house (i.e Fargo, ND, 1550 sf and 2x6 walls, 24" oc. construction...). Layout details that might be available (house on crawl, furnace in closet, supply duct in attic, etc..)

   For most single family homes that are not real unique, the B width (17.5") covers most applications (40 through 100 MBH).

   You find details here: http://www.trane.com/Commercial/LiteratureSearchList.aspx

   or here: http://www.commercial.carrier.com/commercial/hvac/technical_literature/1,3063,CLI1_DIV12_ETI9039_MID4442,00.html

   Always look at the commercial side of manufacturers websites. That's where the real usable data is located.

1. 
   DoRight | Feb 01, 2011 11:36am | #11

   Point of interest

   Thanks Tim,

   Believe me I understand business, bang for buck, customer service, etal.  I realize that businesses are interested in sales and not chewing the crap for the fun of it.  Like you say, I make it clear that I am looking to buy and that it is not going to be today.  I don't spend all day with these folks, just looking for basic information, a few answers and maybe literature.  And they are just plain those rude business guys.  Actually it is all good.  If a guy is like that at the counter I don't want him in my house and likely not anyone working for him.  It is good to know these things before you hire them.

   Lastly, of interest to some, I looked inside my current furnance which is on a basement slab.  In the bottom is a 14 1/2 inch wide by some28 inch deep panel, perfect for 16 oc joist.  I think my thinking problem mostly started from the fact that my plan places my funance crosswise to the joists, thus my thinking the necessity to space the joists wider (frame a hole).  In the case of my current furnance teh joist would need to be spaced 28 apart if I oriented teh furnace in that direction.

   Just for information for anyone reading. 

4. 
   ryder | Feb 07, 2011 01:20am | #13

   Framing for furnace

   I am a framer and not a furnace expert.  That said, we never move framing for furnace requirements unless there is some structural reason such as a beam in the floor system, not under the joist.  For air returns and such the furnace guys use two bays next each other.  The hole in the floor is cut to span both bays and they become one big.  While this may not be what you were asking I will add, again, that in my 15 years of framing 10 to 50 houses a year (back down to 10 these days) we never change the joist layout for fornace issues.  A little this way or that for plumbing is it.

5. 
   DoRight | Feb 07, 2011 12:48pm | #14

   Plenum has joist run through it?

   Thanks Ryder, but are you saying the furnance guys just span tow joist bays and the plenum therefore has a joist run through it?  Seems like that would be hard to seal around.

   Thanks again