Horizontal furnace in the foundation crawlspace

I inspected a house today that had a horizontal furnace/blower fan, and evaporator coil in the foundation crawlspace with the condensing coil a few feet away behind a garage. The system was manufactured by Ruud, was fairly new, and working well, but here’s the rub. I could see the design of this system turning into a lawsuit, quite easily. First of all, moisture had entered the foundation crawlspace, which was confirmed by salt crystal formations on the stem walls and the presence of a float activated sump pump. I could have pointed out that we don’t get much rain in California, but I wasn’t about to. Supposing we happen to get a lot of rain and mold follows, what then? Also the furnace and its blower fan are just inside the crawlspace at one end of the house and, therefore, are not centrally located. And, as we all know cold air falls, meaning that for opitmum design the furnace/blower fan should have been centrally located in the attic. In short, I expressed my dissatisfaction with the design, pointed out one or two other deficiencies, and recommended a specialist evaluation of a relatively new and functional system, thus possibly avoiding a lawsuit.

Great idea Keith…you have a picture of the beast? I have never seen one in a crawlspace, but then again I haven’t seen may crawlspaces here either.


I don’t know, Keith.

It almost sounds like someone who is totally paranoid about the possibility of a lawsuit.

I find lots of furnaces in foundation crawlspaces here, especially in the 750-SF beach houses with flat roofs (so that everyone has a view) that are built so close that they are almost on top of each other (so that lots more everyones can have a view).

Is there really any difference between what you describe and a furnace that is not centrally located in the attic, which happens to be about 75% of the attic furnaces that I inspect.

What if the roof leaks and no one catches it until lots of mold has grown in the attic and been circulated throughout the house. What if the primary drain (or the secondary drain) get clogged and start leaking into the attic, causing mold to grow and, again, get circulated throughout the house through the heating and cooling system. Same difference?

If the furnace was working and installed properly, I would have simply recommended “regular homeowner monitoring and maintenance,” regardless of whether it was located in the foundation crawlspace or attic.

But I am reminded of your story about how report writing has changed. Perhaps you are leading the way to the next generation of report writing:

1 - Kitchen faucet leaks.
2 - Kitchen faucet leaked.
3 - Kitchen faucet leaked and needs to be repaired.
4 - Kitchen faucet leaked and needs to be repaired by a licensed plumber.
5 - Kitchen faucet leaked and needs to be repaired by a licensed plumber before close of escrow.
Keith - Kitchen faucet leaked and needs to be repaired by a licensed plumber before close of escrow. If you move into your new home without having the leak repaired by a licensed plumber before close of escrow, the constant dripping might interfere with your sleep since noises appear to be louder at night since there are not as many noises competing with each other. Lack of sleep might interfere with your job performance, possibly causing you not to get the job promotion and raise that you were expecting to help you pay the outrageous mortgage on your 640-SF dump. The constant dripping might also cause headaches, causing you to have to resort to high-priced medical evaluation and/or prescriptions. The dripping will also waste many gallons of water, thereby increasing your water bill. Without that job promotion and raise, you might be unable to pay your increased water bill, the medical bills, the prescriptions costs, and your mortgage, possibly causing your mortgage lender to foreclose on your 640-SF dump. When that happens, please feel free to contact me for a home inspection on your San Diego River-view property under the I-805 bridge.

Crawl space install is common as well as the dead dinosuar syndrom where the old unit is left under the house. Not to worry.

I like that.

I had a dead dinosaur at one of yesterday’s inspection. I know why they left it, but I will never understand how they got the new furnace in that crawl space. It was by far the tightest crawl space I’ve ever gone into. I think that, in addition to not walking on roofs, I shall quit crawling under houses. I’ll get Ms Margarita and Dr Cuervo to do it for me, if I can get them away from the beaches. :cool:




Russell, the same people put those furnaces in the crawlspaces that put those sail boats in the bottles.

Probably the same guy who put $1,000 in that tiny bottle at the mint, too, right?
I’ve got to make new friends.

Sounds like you are just not used to seeing a combination heat/cool system in a crawl space. The optimum system would be cooling from the attic (yes, cool air falls) and heating from the basement/crawl (hot air rises). But there are many combination heat/cool systems located in either space. It’s considered acceptable practice, and works well if layed out correctly (like any other system), but there should be a combination high/low return.

In my mind the moisture penetration and potential mold (where there is moisture there can be mold) is really a separate issue from the mechanical systems as long as it has insulated metal ducts for distribution. However, if it was an open under floor crawl plenum (no tight metal ducts for supply and/or return) I could see that as being a real concern.

I would have to agree with Robert as an exceptable practice if installed properly but my personal opinion as a past installing contractor I Think it is a straw of last resort and have never personally installed a unit in a crawl space and would have tried to deter the thought.

I have a off beat ethic question but it was concerning the A/C ducts.
I inspected a slab on grade repo in a very exclusive neighborhood with the ducts in the slab. The seller and real estate agent were present and as I was checking the registers for moisture and made the statement to those present that I often made wages for the day by finding dimes and quarters in the registers and I said this as a joke. The seller stated that he would split with me what ever amount that I found. I just laughed and continued on and got to the next register and saw something strange and asked the seller if his offer of splitting with me still stood as there was something in the register back about one foot and he stated sure but if it had hair then I could have it all. I pulled out a pop corn jar and counted out $1001 that appeared to have been there for a long time.

The seller had never lived in this home as he purchased it for a flip.

My question to you guys is who got the money???

So you have NO problem.

Moisture entering the CS is not an HVAC issue.

There are package units installed on the outside of the house at one end of the house. They work just fine.

A point to consider, is that a centrally located unit requires two branch circuits that must proportionally split the air flow. This is much more difficult to calculate and design. A straight run, downsized in accordance with friction loss is the best design if at all possible.

The natural convection of air should not be a concern for air delivery in a properly designed duct system. Natural convection is a factor after the air is discharged from the duct system.

Blocked air flow from floor registers by furniture is a greater concern.

Placing an A/C unit in the attic has detrimental effects in the efficiency of the HVAC unit due to the excessive temperature extremes found there in summer and winter. It is the last place I would consider placing the unit, but is where it needs to be a lot of the time. Still, not the best choice of location.

I’ve seen tons of such installations, and never really make a fuss. I just make darn sure that I don’t completely endorse such a design. Remember, what I said about its return-air grill location, not simply being under the house but at one end of it. The air-conditioning was working nicely in the living room, kitchen, and laundry room, but the volume of air in the bedrooms on the opposite side was weak, and the rooms was decidely warm. Knowing what I know about how inspectors have been victimized, and wishing to serve my clients as best I can, I’m only going to endorse an optimum design. Gentleman, you’re all calling it very intelligently and as you see it, and I congratulate you all. Let’s keep on sharing, and agreeing to dissagree.

P.S.Oops. The return-air grill was not under the house. It was at one end of the house, above the unit, and close to the floor. It was also limited in size, about ten-by-ten-inches.

In the olden days, we built (maybe I built is better) houses with the inflow register on an exterior wall of a room and the return register on an interior wall. We don’t do that anymore, preferring to let the bottom of the door serve as the return register. So my question is this, “How many of you check to make sure there is ½” to 1" of clearance at the bottom of the door?" I regularly find that such clearance is minimal or nonexistent after the new carpet people have been in and educate my Clients about what can happen in a home when good circulation is not present.

This has to do with duct design, in a perfect world with the right contractor there is more than one return and the duct is completly sealed. Its all in the layout.:smiley:

I have a built-in narrative about the necessity of doors being undercut. Don’t always use it, but it’s there when I want it.

P.S. This “design” thread got interesting. Just when I think I’m close to an appreciation of how things work, someone throws in their two cents, and I’m left wondering. Take the temp split thread, for instance, I take temperature splits religiously, at every register, and find it difficult to understand that it’s not valid. I hope spomeone at the NACHI conference will undertake an HVAC workshop, and clear up some of the mystery.

What would you tell me about these splits:

1 - 14° split, 64° and 78°
2 - 14° split, 70° and 84°
3 - 14° split, 76° and 90°

They all are 14° splits. In the first one, I suspect that my Client who likes it 80° or warmer during the winter ain’t gonna be too happy. In the third one, I suspect that my Client who likes it 74° or colder during the summer ain’t gonna be too happy.

That’s why I don’t use splits. They are kind of like percentages. Which company would you rather own:

Company 1 - 1000% growth between year one and year two
Company 2 - 10% growth between year one and year two

Better seek additional information. Company one increased from one sale to ten sales. Company two increased from 1,000 sales to 1,100 sales.

Now if standards required that the bottom end of the split be between, say, 60° and 70° and the high end of the split between, say, 85° and 90°, then I could possibly see value in determining the split.

Now you are talking about some issues with the mechanical system that can be reported on, and would further support the call for evaluation.

Much warmer rooms may indicate an installation problem (I don’t like using the word “design” for home inspections, just to avoid even the appearance of reviewing that). That could just mean the system needs to be balanced, or there really are layout/sizing problems … but leave that up to specialists.

For the typical single return residential system, the return grille should be more centrally located as it’s difficult to draw warmer return air all the way across a house, particularly with any closed doors without a sufficient bottom gap. It’s also more difficult to effectively get conditioned air to the end of a long trunk run (especially if it doesn’t step down correctly), or a system with a lot of flex duct. And the return size does seem unusually small, which could restrict flow and also be noisy.

P.S. One clarification on a previous comment. While I usually think of moisture penetration as a separate issue from mechanical systems, excessive moisture over time may reduce the useful life of many things … including mechanical systems nearby.

JMO & 2-nickels … :wink:

Even though I disagree with the “Split”, I also take them!

BUT, you can not use the information to determine the PERFORMANCE of the equipment. Your using the wrong tool for the job.

There is a workshop in CO.

The problem with some of this HVAC information is that so many are trying to do too much with too little.

Air duct design is another whole area in the HVAC world. It also has a direct effect of “Comfort” in the house. There are many reasons for low air flow, long straight runs from one side of the house to the other is not necessarily one of them! Did you know, you get more air pressure at the end of a 60 foot straight duct run than at the first takeoff at the unit? Why? Air (like water) does not like to change directions. Remember “things in motion want to stay in motion”? Before air will turn at the first takeoff, the air must hit the end of the 60 foot duct and build up “static” pressure, which forces the air sideways.

Turning the air flow results in a Dynamic Loss which results in this low air flow at the first takeoff. The air flow through the straight run of the main trunk line has less resistance, therefor the air passes towards the path of least resistance and does not readily change direction.

Have any of you seen the ranch house with an attached garage on one side of the house that was converted to a family room? Often a supply register is installed off of the end of the main trunk line. The result is a massive amount of air flow into that room and a resulting drop in the rest of the house.

Return duct as well as supply ducts must be balanced! Not a 10 x 10" !