Install Hard Ductwork?

[BigCTM]

I have a single story house with a 350 sq. foot bonus room upstairs above the garage that is VERY HOT compared to the rest of the house. The other issue is that the rooms on the side of the house away from the unit are VERY COLD in the winter.

I have received several estimates. Two of them suggested adding a vent and a return in the bonus room and moving the supply on top of the unit with a damper instead of on the side for increased air flow. The problem I have with this is that it does not help the issue with the rooms on the opposite side of the house. In fact, this solution would make this worse more than likely.

The solution that seems the best involves installing lots of hard duct from the main trunk with dampers and then running flex lines connecting supply outlets to main trunk. They offered to do all hard duct but it was significantly more. This also involves doing a load calculation to ensure that the current system will support the room above the garage. The bonus room would receive a new vent and a new return also.

The current system is all flex and there are some long runs, especially those going to the other side of the house. Does this sound like a workable solution? Would zoning like Arzel or Carrier Infinity be another possible solution? Thanks for any suggestions.

[marlboroman]

we always use 2 units if the house is 2 story... When you stretch duct to a certain point, you will start to loose air flow, and heat and cooling to those rooms.


you could zone it, but a good contractor with a J should know if that unit can handle that much more... Also it is hotter in the 2 story part then the rest where insulation is covering the ceiling. Also if it is over a carport, then think of the heat under you... I would think just from what ya said I would put in a second system. your already having problems trying to cool and heat the house.

[bmathews]

If it's in your budget, metal pipe is great. I would get them to balance what you have if it is possible and install a PTAC or minisplit in your bonus room. I think adding an entire split system is a bit of an overkill for such small sq. ft. If you go with zoning, don't make it 2 zones, go for at least 3. You will still need to fix your ductwork, a zoning system can help with bad ductwork to a point, but generally will not fix your problem. Your contractor hopefully can help you along. I would call somebody else out to give an opinion as well.

[beenthere]

If you can find a contrator that will do a room by room manual J, so they know how much air those rooms need, they will be ale to determine if the supplies are the right size.

Those rooms that are cold, may just have undersized supplies.
As for the bonus room. They are best served by their own systems. A mini split usually works great for those rooms. PTACs are ok, but if the bonus room ever gets converted to a bedroom, some people don't like the noise you can get.

[rundawg]

The current system is all flex and there are some long runs, especially those going to the other side of the house. Does this sound like a workable solution?

Contractors love flex duct. Flex duct is inexpensive and easy to use, but it's spiral wire-helix construction also means higher friction loss compared to sheet-metal duct or fiberglass duct board. Compression or bending, the very attributes that make flex duct so popular, cause the inner core to change shape, which increases turbulence and friction loss - resulting in reduction in equipment efficiency, and in the over all life of the system, costs the homeowner thousands of dollars in higher utility bills. Some contractors' remedy to poor air flow is to install oversized equipment rather than address the real problem - poor duct work.
Some states restrict the use of flex duct to 5ft or less at the end of a sheet-metel duct run where the metel duct connect to the register box. This type of "Hybrid" duct system will maximize the efficiency of metel duct while using the convenience of flex duct to make that final connection to the register and minimize HVAC system noise.

[beenthere]

What states limit flex duct?

Architects, and engineers do on their prints.
And IMC limits the length of flexible duct connectors, but has no limit on flex duct.

[rundawg]

[QUOTE] What states limit flex duct? QUOTE]

In an attempt to be brief, I didn't add " some cities in states like Arkansas and Colorado have adopted local code amedments that limit the use of flex duct". These are not state wide codes.
Sorry for the generaliztion.

[jramunni]

I have a single story house with a 350 sq. foot bonus room upstairs above the garage that is VERY HOT compared to the rest of the house. The other issue is that the rooms on the side of the house away from the unit are VERY COLD in the winter.

This also involves doing a load calculation to ensure that the current system will support the room above the garage.

The current system is all flex and there are some long runs, especially those going to the other side of the house. Does this sound like a workable solution? Would zoning like Arzel or Carrier Infinity be another possible solution? Thanks for any suggestions.

If there are duct improvements that should be made, than you should definitely consider doing that. Long runs of flex duct will deliver minimal air (capacity).

Does your equipment (htg/clg) cycle off during harsh weather conditions (peak load temperatures) or does it run non-stop? If it is cycling off, then you have extra capacity that could be directed (via zoning) to the hard to heat/cool areas during those off cycles. If not, than you should have a manual J load calculation done, install properly sized, two stage equipment and add zoning to get the capacity into your trouble areas.

Yes...It really is that simple!

[beenthere]

[QUOTE] What states limit flex duct? QUOTE]

In an attempt to be brief, I didn't add " some cities in states like Arkansas and Colorado have adopted local code amedments that limit the use of flex duct". These are not state wide codes.
Sorry for the generaliztion.
The AHJ has that right.

Now, just curious, does their code say flex duct, or does it say flex connector.

[rundawg]

[quote=rundawg;1837489]
The AHJ has that right.

Now, just curious, does their code say flex duct, or does it say flex connector.
beenthere : I don't know the answer to that question for sure, but I think they mean flex duct, not connectors . I was talking to Chris Van Rite, the author of a recent article in the RSES Journal about flex duct, and he didn't mention to me which one. Here is his email: Maybe he can answer that question. Great article.