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View Full Version : Advice to "harden" basement AHU & ducts



dbliss3593
03-31-2012, 01:48 PM
Ok Experts, here's a really tough situation:
I need to "waterproof" my basement AHU/ductwork as best I can. Any suggestions? Here are the details: I own an old stone farmhouse situated about 100 feet of a large creek that regularly floods into my basement. My HVAC guys installed a spacepak system for the 2nd & 3rd floors that runs very nicely; 1st floor is supplied by a separate low velocity system, ducts in the basement. Problem is the basement floods periodically, sometimes high enough to get into the HVAC systems. The air exchange unit in the basement was replaced in July 2011 from a flood the year before, and within a month Hurricane Irene damaged the new Trane 4TEC3F30B unit, as well as depositing a fine layer of dirt in all the plenums and steel ducts. The AHU sits on a pier about 5ft above the basement floor. Yup the creek water rose into the basement above even that point. Because we knew Irene was a-coming, we pulled the motor and circuit board, but the insulation around the interior of the unit was soaked. We've thought about removing the systems out of the basement altogether, but no alternative is as unnoticeable as the current setup. For example we considered a mini split system, but the inside unit mounted above a window that would be much more obvious than the current setup: 7 supply registers and 2 returns in the floor. We also considered extending the 2nd/3rd floor spacepak system to the 1st floor. As our old closets were tiny, new chases would need to be added, a more intrusive option. So at this point we've decided to just "harden" the basement systems as much as possible. So any suggestions for making the AHU and duct work easy to remove & clean would be a help.

dbliss3593
03-31-2012, 01:51 PM
I should add that I would pass recommendations onto my HVAC guys.

Gib's Son
03-31-2012, 02:04 PM
Interesting.

Double wall duct with aluminum jacket exterior. (insulation between exterior jacket and interior sheet metal.) Seal seams and joints with duct sealant suitable for outdoor use.

The air handler presents a tougher challenge. I would relocate to floor above or try and make horizontal, hang tight to floor joist and build a soffit around it with access panel large enough to service and remove.

That' my first thought.:.02:

skippedover
03-31-2012, 02:57 PM
We encountered a similar situation several years ago except that it was ocean salt water the infiltrates, just to add to the mix. We did replace the entire duct system with new metal duct but rather than using wrap insulation, we used dense spray foam. there was no velocity to the water entering the crawlspace, it was just the height of the water. We put the high efficiency furnace in a closet on the first floor level, connected through the floor to the new duct system. The use of dense foam solution was to both prevent water soaking of the insulation as well as to seal the ducts and provide a 'foam duct' system, if you will, if the salt water did get into the ducts and rust out any part of the ducts. The folks who owned the home moved before we really got a chance to observe results as the new owners signed up with the gas utility to do their repairs and minimal maintenance. So I can't give you any specific results but it's worthy of some consideration methinks.

dbliss3593
04-02-2012, 12:05 AM
Skippedover, The dense foam insulation idea, seems to me to have real merit. My only concern is that debris might accumulate on the interior after each flooding. I envision dismantling the ductwork periodically for a thorough cleaning.

Both Gib's Son and Skippedover suggest moving the AHU to a higher location. This may be possible if difficult and expensive. It will require digging a trench on the exterior of the house to a point where then a hole can be made in the 20" exterior stone wall. Insert a steel lintel. Install the AHU above the potential waterline level, and run new ductwork from the AHU down into the trench, through the wall to connect up to currently installed ductwork in the basement. Whew! Maybe $3-6K of work. And I suppose the AHU should be protected from the elements and out of sight.

Thanks, Gentlemen, for your help.

SolarMike
04-02-2012, 08:37 AM
How about putting a tankless boiler, like the Navien and doing DHW and run some baseboards or panel rads. The boiler could be in a main floor closet.

dbliss3593
04-02-2012, 07:36 PM
SolarMike,
Sorry, I didn't make it plainer, but it's just the air conditioning system that needs to be "hardened." Many years ago we installed a System 2000 boiler in a unheated c. 1850 stone-walled first floor extension to the house. To connect the boiler to the pipes in the basement, we ran 3" copper from the boiler about 20 ft through an overhead crawl space, piped down to the basement through a small closet chase, through 20" stone wall and into the basement. Those old radiator pipes are the ultimate "hardened" system, I think. Three old boilers remain in the basement, too costly to break up and perhaps full of asbestos.

Gib's Son
04-02-2012, 08:01 PM
I too kinda like skips recommendation. Just not sure of it's longevity, especially after becoming wet. I suppose it would be ok as I have seen exterior ducts sprayed with foam. FYI, the method I mentioned is the method I use all the time for exposed ducts on a roof, subject to extreme weather conditions, and it outlasts the equipment.