Without being a HVAC tech. Its simple count the registers if the ducts are in the crawlspace or in the attic. Your out of luck on a slab foundation you can not count the registers.
On a 12 inch diameter duct if you can see no more than three 8 inch drops to the living areas and one 4 inch to a bathroom you can rest assured that the air flow will be adequate. I occasionally see 4 eight inch drops on one 12 inch trunk but that is where the inadequate air flow begins and the complaints start with the home owner about being to warm in the summer and to cold in the winter.
I don’t as a home inspector measure air flow at the register but if I see excessive drops on the trunk line I will put in my report for the buyer to expect a temp differential within the home that may not be satisfactory and that the air flow should be adjusted accordingly. This is just a visual inspection nothing more. The Duct system is probably the most ignored system of a home inspection
What you say sounds reasonable and I don’t doubt that it would act as you say. Do you have a link that inspectors can put in reports as a help for client/agent/others understudying? I mean, besides “Charley said so”…which, should be enough, I know. :p:mrgreen:
If you measure airflow a rule of thumb is 1cfm / sqft
a 6 inch duct to a room only feeds roughly 90 cfm. this would be adequate for a normal 9x10 bedroom.
Guess ya will just have to say (Charley said so) Larry they don’t measure air flow by the amount of duct boots or drops installed its all CFM. I was just trying to provide a heads up to look for during a inspection based on all my years of doing that type of work as a means to suggest further investigation by a qualified contractor that can actually measure, balance and or adjust air flow. When walking in the attic I just mentally take note of how many drops are installed on a trunk line its a habit same with a crawl space just cain’t help it;-)
It’s late here, but I’m having trouble with 4 drops = things are OK.
12" duct vs. 18" duct. 2 ton vs. 5 ton. Your load vs. my load. Your friction loss, Denver’s friction loss. Furnace only vs. Heat Pump.
Are you sure you want these guys messing with this stuff?
Yea, it works for you, there.
But not too many here can tell you what’s what beyond a 2 ton heat pump (which should have a 14" to start with here). ?
Now I need to find a house with A 9X10 BEDROOM. Pantries are bigger than that where I work…
We use .85 cfm/sq.ft. here.
And to really mess things up, the return size has everything to do with anything.
A 1" pleated filter can throw everything out the window (and take out the heat exchanger)!
Please, don’t take these guys there! This is INACHI not OkNACHI. Just too many variables out there.
with all the hvac crap (can’t relly apply properly) seen & consumer comfort complaints i’d tread lightly in adopting a 1 size fits all strategy http://www.nrel.gov/docs/fy12osti/53352.pdf
The cause for the uneven temps covers a wide range of issues.
I think with all due respect, these issues should be “avoided” by Inspectors and left to the people who’s job it is (even though only 1 in 10 know what you know).
It’s hard enough to find someone that knows duct design in the HVAC field. It is Ludicrous for a client to expect anything more from an Inspector.
Just my experience…
From Barry’s link; First sentence of the first page. Department of Energy.
I agree with the who’s job it is to fix the problem but someone has to start the ball rolling. Most inspectors just disclaim the duct system and try to ignore it based on some silly SOP. As inspectors we should be able to at least recognize there is a problem and direct the problem to the correct trade.
It may be ludicrous for a client to expect not to have rooms that don’t cool or heat evenly but believe me they do expect it why do we get so many calls on this. Not me personally but some do its always the inspectors fault its never the dumb A** that installed it to begin with.
Speaking of dumb A**'s one of my inspections yesterday had a full basement with the furnace in the basement closet, gas fired with the flue pipe traveling thru the return air duct by means of a hole cut thru the duct. The return air never had a filter installed since 1986 the coil was changed out in 2000 because it was not cleanable and then the dumb A** did the same thing all over again no filters installed since 2000 and wondered why no air flow. Yes there are lots of things that create lack of air flow but again as inspectors I think it is our obligation to start the ball rolling even if it is not in the SOP. That is my story and I am sticking to it.
I thought that was our job was to get the ball rolling, yet those of us who do are called deal killers, and we should have the rollback our price thing going on and give them the world for it, hmmm. :roll:
And why is that its an inspectors fault.
I operate the hvac equipment using normal controls (thermostat) if appropriate given exterior temps.
I check vent temps with infrared thermometer to determine if all vents are operating.
If I find most vents are at x temp and one vent is at ambient temp. then I note that.
For cooling I like to see temps of 65 degrees max or less at the first floor vents if the unit is located in the basement.
Anything more and I recommend hvac tech evaluation.
Perfect system? No.
I feel comfortable with it and have had no complaints.
