I’m doing an addition and renovation to my 1950’s split-level home. When finished, there will be 4 separate finished levels, all open to one another. As you can imagine, with the original single hvac system, the higher levels are always warmer than the lower levels.
So, we’re installing two independent systems. One for the higher two levels, and the other for the lower two. For the high system, the furnace is installed in a small closet on the highest floor, off a corridor to the master bedroom.
I was hesitant to do this (having a machine to make fire on the same level as a bedroom just seems wrong), but everyone insisted that is “what’s done”.
Tonight while looking at the octopus of ductwork that rises from the furnace into the unheated attic space, I realized that the closet has no ceiling, and that I can’t imagine how one could isolate the closet space from the attic space given the mass of ductwork that would pass through any attempt at a ceiling.
I’m assuming that this is bad – that warm, humid air will rise into the attic space, where it will condense on the underside of the cold roof framing in the wintertime, keeping it all nice and wet.
Being a pessimist, I’m bracing myself for being told by the general and subcontractors that “it’s fine – not to worry!”, and I’m looking for ammunition to counter their argument.
Am I right? Is this as bad as I think it is?
Any suggestions for “fixing” the situation?
The ONLY way I can imagine one could come close to fixing this, short of starting over, will be to create a massive blob of insulation over and around the ductwork, sort of like a wasp’s nest of insulation, wrapped by a colossal sheet of vapor barrier that is brought down to the side walls of the closet.
Thanks in advance for any advice or feedback.
p.s. – another concern of mine is (was) heat buildup in the furnace closet when it’s working hard during a sub-zero cold snap here in Chicago. Assuming that this closet can ever be sealed, what is done about this? Should there be ventilation of the closet itself, either passive (via door grilles, chimney to the roof, etc.) or active, via a dedicated exhaust fan?
Replies
Around here hvac is put in the attic every day. I'm in NJ and it gets cold here. Every add-a-level I frame they go in the attic.As long as it's done right you shouldn't have any problems.
Well, since the error is in the first paragragh (the upper levels being warmer than the lower levels somehow being attributed to having one furnace), what more can be said? You seem to be solving a relatively simple system performance / tuning problem with a sledgehammer.
I suspect that with more return ducts and proper system balancing, the temperature distribution could have been fixed...but it's beyond that now, so we'll politely bow out.
HammerHarry wrote:
Well, since the error is in the first paragragh (the upper levels being warmer than the lower levels somehow being attributed to having one furnace), what more can be said? You seem to be solving a relatively simple system performance / tuning problem with a sledgehammer.
I suspect that with more return ducts and proper system balancing, the temperature distribution could have been fixed...but it's beyond that now, so we'll politely bow out.
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Well, since the error is in the first paragraph (assuming that the original, primitive, anemic system with the perforated heat exchanger, the leaking A/C coil, the undersized, serpentine ductwork and the various Rube Goldberg "improvements" that the last 4 frustrated owners made, could have been "tuned" into not only properly serving a building type that is notoriously difficult to heat/cool evenly, but could have accomodated a sizable addition) what more can be said? You seem to be assuming that we had no idea that an hvac system needs to be properly designed and balanced, and instead just reached for the nearest sledgehammer.
It's a little more complicated than that, but thanks anyway.
I was just reading what was written. I have that habit. There was a clear statement that the upper floors were warmer "of course", or words to that effect.
My apologies for not interpreting the words not written. Next time, I'll assume a whole lot of things that aren't said, just on the off chance they happen to be true.
Rarely done here (MN), but it seems to be common in other parts of the country.
The ductwork needs to be very carefully sealed, and probably should be insulated.
It may be best to create an insulated enclosure in the attic for the bulk of the ductwork, so it can be included in "conditioned space".
I'm assuming that this is a high-efficiency closed-combustion condensing furnace -- that would make the most sense in this situation. Properly installed, such furnaces throw off very little heat, and need very little ventillation. Not sure what code requires, but practically speaking a louver in the door or a couple of registers (hi/low) in a wall should suffice.
I would seal the door to the closet (weather stripping) and also seal and insulate the closet. But it the furance is in that might not be possilble.
Also you can convert the attic into conditioned space by insulating the underside of the roof and removing any venting into the conditioned space.
Here's a couple pics of a house I framed with the HVAC in the attic.
1. Yes, the mechanical closet needs an airtight ceiling. It may be difficult, but it is essential.
2. Ceiling insulation needs to be installed above the ceiling of the mechanical closet.
3. Any ductwork in the attic needs to have seams sealed with mastic or high quality tape and needs to be well insulated.
4. It may be easier to insulate the attic rafters than to do the above steps.
5. The furnace needs adequate combustion makeup air. If it is a sealed combustion unit, you're all set. If not, be sure your hvac contractor knows how to calculate the combustion air needs of the furnace.
The way the installation should be done is with an insulated plenum extending up through the ceiling of the furnace closet into the attic space. This plenum should be provided with 1" fiberglass duct liner. At the ceiling penetration, the opening should be framed out, dry-walled and sealed. The plenum should extend into the attic far enough that all of the octopussies tenticles can be connected to the plenum in the attic, not in the closet. One penetration through the building envelope is better that 8. Not having a ceiling is not acceptable. Sounds like you have been victimized by a hack. Good luck.
Furnace in the second floor closet is not a problem. I am assuming the furnace is a high efficiency unit. It needs to be in a conditioned space. The closet work, however, my preference is an insulated attic. Don't forget to provide a code required drain pan under the furnace connected to a waste line. Be sure to have room to service the furnace. As a high efficiency unit don't forget to bring in combustion air to the unit with 2" diameter PVC pipe from the exterior, either through a wall or through the roof, and you also need to vent the unit also with another 2" PVC pipe once again, through the wall or through the roof. The ducts running in an uninsulated attic need to be insulated. Don't just drop some insulation on top of the sheet metal ducts, the ducts need to be insulated ducts, or if the attic is insulated, the ducts don't need to be. There will be heat build up in the attic, but code once again required you to vent the attic with soffit vents and attic vents. I'm in Chicago and any inspector will make sure you do the job right.