Cold Air Returns

IHI

I need some help, i bought this 28x40 single story ranch i grew up in, even as a kid the north side of the house where the 3 bedrooms are located have ALWAYS been colder than the rest of the house. I have installed new windows throughout, removed 2 windows on the north side since there's nothing to look at but the neighbors wall of their house. Installed a HE 65,000BTU furnace and have the intake/exhaust PVC exiting on the north side of the house, so it uses the 2" PVC plumbed into the furnace itself along with the cold air duct that has the hood on the east side of the home. I installed a digital thermostat to cut it back when we're not home, and night time, daytime setting to be comfortable is 74*...bedrooms are commonly 8* cooler than living room. I've taped all joints on ALL duct work, insulated the ducts branching off the truck line, basement is finished and we installed a cold air return down there when finishing it in the main living room down there. House is 2x6 walls with fiberglass batts. I've also done some tweaing on the dampers in the ducts to try and cut back the main living area's outputs to try and increase air flow to the further regions from the furnace, for the record the furnace is located approximately 26' away from the north side of the house.

SO, last night i had some buddies over watching the fights and the one is an HVAC tech, i told him about the cold azzed rooms and he said we need to install some cold air returns into each bedroom and that will make a day and night difference and offer a more even heat back there..and for the record we often keep the doors to the rooms back there closed and pen the dog up in the hallway when we're gone so they're closed most of the time so that is'nt helping. Currently the ONLY cold air return upstairs is in the hallway itself, and that was the only one we had prior to finishing off the basement.

Question to you guys in the feild, will this help the situation with trying to get heat back there in the back bedrooms?
How large do i/we need to the return ducts to be since i've been reading a bit and "they say" you want it evenly sized for air in/air out. all the ductwork is 6" round tube and all the bedroom vents are 2x12 floor registers on the outside walls under the windows.

please tell me what i can do to help this situation, the HVAC stuff is something i've never gotten into much and just made phone calls, but obviously since this is my personal house i'll have my hvac buddy give me a hand with the technical stuff but i will be involved too, i just want to be sure a proper balance is achieved if it's a detrimental part of the equation...HELP!!

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Tom M

Not an HVAC tech but I will agree with what you say that your not removing enough cool air from the rooms. Obviously because the doors are closed the central return is satisfied by the main living area first. They make louvred jumper vent that you can install above the door openings that simply share air from joing rooms. They will transmit some sound but also provide an easier cool air exhaust if the central return is in the ceiling, if the return is low you should make sure any carpeting is not blocking the bottom of door openings.

joasis

The quickest way to know would be to leave the doors open.

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loneframer

From a carpenters view, how much space is there between the finished floor and the bottom of the door? In homes with central returns, we try to maintain 3/4 of an inch for return air draw. If the central return is near the bedroom doors, it should pull fairly well. If you already have a decent space, insulating the ductwork may have an impact, especially that far from the unit. If those solutions don't work, adding a return in the rooms should help. I would try these in order to solve the problem.

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IHI

I dont wanna put louvers in the walls above the doors...i'd hate to give my daughter emotional scars when i'm hammerin on her mama

When i was a kid, and just like before we got another dog..we had a 3 yrs window with no pet that ended this past august, the doors would be left open and it made zero difference...the north end of the house has always and still remains colder than a witches t.t, you feel a DRASTIC difference about half way down the hall, then once you enter the rooms, even with doors left open, it's like walking into a commercial cooler when compared to the temps int he living room.kitchen.


I've installed all new oak floor/doors, tranition strips between the hallway wood floor into the carpeted bedrooms so the space under the doors is minimal...i opted for a heavier pad under the carpet and the doors juuuust graise the top of the carpet fibers throughout the swing. Ducts are taped at joints and insulated already.

I'm not doubting what my HVAC guy was telling based on a few flip homes we've renovated all the different HVAC ccompanies install returns in EVERY room in the house, and even my buddy told me on all the new homes they work on, they install cold air ducts in all the rooms since it creates a constant smooth airflow/cycle of air, so instead of making the furnace try to pressurize a room, utilizing the cold air returns in each room actually depressurizes it allowing the furnace to flow freely...he said it's like blowing into a straw that is tapered down on one end to almost nothing vs blowing through a straw that's the same size all the way down...which is easier to move air through...so that made sense to me, but i "read" the system needs to be balanced, just like attic venting, so you dont create a different circulation problem, then the one your trying to overcome in the first place.

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Tom M

So your making it worse. Trim those doors and insulate those ducts.

loneframer

If leaving the doors open had little effect, installing cold air returns probably won't solve your problem either. I'd still cut the doors to promote air exchange in the rooms. It is probably in your best interest to pursue problems with air infiltration/insulation. Start in the attic, as it is usually the easiest place to add insulation and is the area most prone to heat loss. If accessable, insulate the joist bays in the basement along the outside walls, as well as foaming any gaps. Caulk any window casings along with spaces around replacement units. Install foam gaskets behind receptacle plates. Look outside as well. Depending on the type of siding you have, there may be ways to reduce air infiltration. You may be looking at a long list of small jobs to get the optimum results.

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IHI

LOL, i've now got two posts saying i DID insulate the ducts prior to finishing off the basement.



When i redid all the windows/doors/siding i also went into the basement, pulled away all the previously installed batt my step dad installed between the floor joist cavities up on top of the sill plate. I took and expanda foamed all the way around each spread web joist end to where it meets the rim joist then cut and installed new fiberglass batts and placed them up against the back of the rim joist. The attic, when i resided the house i removed all the plywood soffit, did the math for intake/attic venting and installed chutes to achieve a proper 25/25/50 intake to exhasut ratio. Once i had all the poly chutes installed between the truss cavities the original cellulose blow in had settled to about 8" thick. So i took and blew in 36" of cellulose back into the attic which took them "about" to the opening on the poly chutes that now feed fresh air into the attic, i did'nt do the math for the attic but i have to assume R factor is well into the R-40 range with over 40" over cellulose up there.

Believe me, knowing how cold this house was as a kid, i made gawddarn sure when i started giving it a make over i addressed everything i could to help tighten it up to help TRY and make it warmer. At this point, i'm at a loss, and after my buddy mentioned doing cold air returns in the rooms i thought maybe that was the missing link and theoretically it sounded good, but i wanted more opinions. The plan of attack now, we plan on adding on a 16x40 addition to the back of the house next spring/summer so i can build the shop out back i want (city regulation i cant have a garage larger than the house so i have to add on to house while doing the shop) but i'm going to strip the siding off the house back down to the horse hair board/fiber board, install Tyvek over the shell, remove and discard all the new vinyl windows, buck each opening with 2x4 and 1/2" plywood and then install 2" ridgid polystyrene over the entire house/exterior, tape the joints, install new WOOD windows to help cut down on radiating cool like you get with vinyl windows. and pray that after all of that, the stink'n place will stay warmer...but something is still preventing the heat from getting to and staying at the bedroom end of the house.

The only thing i have'nt done yet is the outlight/light switch gaskets, and i'm at that point now thinking maybe eventually all these little things will help...though thus far even after everything i've done, the hosue is no better now then it was when i was a kid

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beenthere

As said earlier. if leaving the doors open, didn't help any. Then adding returns will be an excercise in futility.

Your supplies are most likely TOO small.
Meaning your duct work is the typical undersized duct that is in many homes.

Next, a 2X12 floor register moves very little air. So wrong registers, if you want more then 60CFM to the room.

Ask your buddy, if he can check the static pressure your furnace is working against. To the furnaces fan data chart. So you can see how much air its moving.

How big are these bedrooms?

IHI

Thank you for that info, it will give me something worth while to have him check out vs going through the motions for nothing.

Bedrooms are typical 2- 12x14's and 1 14x16

Main trunk line that comes off the furnace and runs the length of the house is 8"x14". All the ducts that come from the 8"x14" truck to the vents in each room are all 6" round and then like noted 2x12 registers.

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beenthere

14X8? Good grief, thats small for a 65,000 BTU 80 or 90% furnace.

IHI

supposed to be a 92%

What are ya thinking? and also do you think it should get progressivly smaller as it gets further from the furnace too? or would increasing trunk size alone be just fine? would the 6" branches be alright too? or should those also be upsized? register size? if we increase size of all of that, would it then be a good idea, so long as we're ripping and tearing, to cut in fresh air returns in each bedroom?

Lemme know what your thinking as i want this problem fixed, i'm tired of the house being like my wife, hot and cold....no in between

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beenthere

The trunk staying one size for its full length is ok. Since its short.

You should do a load calc. And see what size furnace you should have. And also. A room by room load calc, will tell you how much heat each room needs. So you can size the branches to each room properly, instead of guessing.
This program is easy to use. It has a small fee, and your buddy might be interested in checking it out also.

Probably your 6" runs to the upstairs, are all undersized.
If you have no under cut on your bedroom doors. then while redoing the duct work, it would be a good time to add them. Since the air will need a way out of the rooms.

You may want to go to 4X12 floor registers. They will flow more air easier.

IHI

thanks for the insight beenthere

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beenthere

Your welcome.