My cheap idea for fixing uneven air temps in different rooms

[robolo]

I installed one a few years ago They're very effective at sucking all the smoke out of the house when the wife burns the dinner too.

LOL. The iced tea I was drinking came out my nose on that one!

 

[pete]

before taking steps to automate that may cost additional energy (not that expending energy to be comfortable is bad, just that you should seek best return on expenditures) you should be sure your system is as balanced as it can be . . this will not correct an extreme uneveness between areas, especially because of east/west exposure differences (best to balance at noon, I guess) but will get you the best performance from your equipment

see this page . .

http://www.ehow.com/how_2074293_balance-hvac-air-flow.html

I actually use a few instant read thermometers, one in each room, keep balancing 'till they're all reading as close as you can get them . . also be sure there is an adequate return air path . .

 

[hucker]

This balancing problem is harder than you think because you are trying to make a static system of

* fixed vents/registers
* single temperature sensor at tstat

balance a dynamic system where

* each room has a different heat loss/gain
* the relative heat loss/gain varies with time of day and time of year
* each room's door may be open or closed
* rooms are used at different times of the day.

We have two rooms that have floor over garage and two exterior walls. These rooms are ALWAYS cold by about 3F vs the setpoint and 5F off of the warmest upstairs room. We have under cut the doors and have full air flow to these rooms. In the spring and summer the problem was less pronounced.

I am still working this problem but I think to provide 365/24/7 balance more dynamic elements (registers, zones, fans etc) are required, or your standards need to be reduced.

Disclaimer: I am not an HVAC guy, just an engineer who knows enough to be dangerous!

 

[pete]

This balancing problem is harder than you think because you are trying to make a static system of

* fixed vents/registers
* single temperature sensor at tstat

balance a dynamic system where

* each room has a different heat loss/gain
* the relative heat loss/gain varies with time of day and time of year
* each room's door may be open or closed
* rooms are used at different times of the day.

We have two rooms that have floor over garage and two exterior walls. These rooms are ALWAYS cold by about 3F vs the setpoint and 5F off of the warmest upstairs room. We have under cut the doors and have full air flow to these rooms. In the spring and summer the problem was less pronounced.

I am still working this problem but I think to provide 365/24/7 balance more dynamic elements (registers, zones, fans etc) are required, or your standards need to be reduced.

Disclaimer: I am not an HVAC guy, just an engineer who knows enough to be dangerous!

I am an HVAC guy, for 20+ years now . . I understand your points, that's why in my post I said " this will not correct an extreme uneveness between areas, especially because of east/west exposure differences"

the only way to achive perfection would be seperate systems for each distinct area with different loads, not an economical choice for residential installs . . so we do the best we can

assuming we're in heat mode, all regisers full open, if you limit air flow to the warm room(s), that air will go somewhere . . keep balancing until it ends up in the cold room(s) . .

you could do load calculations, get an air-flow hood, and balance that way . . but the end result will be the same . .

and either way may not be perfect, but at least your getting the best performance out of your equipment . .

if you want to automate a few outlets at this point to achive greater comfort, go for it . . limit (don't cut-off) air to the over-conditioned spaces and it will end up in the under-conditioned spaces . .

 

[hucker]

I am an HVAC guy, for 20+ years now . . I understand your points, that's why in my post I said " this will not correct an extreme uneveness between areas, especially because of east/west exposure differences"

the only way to achive perfection would be seperate systems for each distinct area with different loads, not an economical choice for residential installs . . so we do the best we can

assuming we're in heat mode, all regisers full open, if you limit air flow to the warm room(s), that air will go somewhere . . keep balancing until it ends up in the cold room(s) . .

you could do load calculations, get an air-flow hood, and balance that way . . but the end result will be the same . .

and either way may not be perfect, but at least your getting the best performance out of your equipment . .

if you want to automate a few outlets at this point to achive greater comfort, go for it . . limit (don't cut-off) air to the over-conditioned spaces and it will end up in the under-conditioned spaces . .

Pete:

I appreciate your reply and I understood your caveats.

When speaking to our HVAC contractor he won't even go to the point in acknowledging that there is a problem since he balanced the system. In our house these two rooms are an extreme case where our cold rooms have 3 of six sides seeing outside our unheated garage, while the other bedrooms only see one outside wall. It just doesn't look like this can be balanced out. Exacerbating this is the fact that I think these two rooms suffer a design flaw on his part as the registers are very close to the doors, thus providing a short circuit for the hot air to follow. Further exacerbating the problem is that the cold room is the babies room... very low WAF IYKWIM.

 

[drozwood90]

This is why I monitor pressure / temperature / humidity of each room.

--Dan

I am an HVAC guy, for 20+ years now . . I understand your points, that's why in my post I said " this will not correct an extreme uneveness between areas, especially because of east/west exposure differences"

the only way to achive perfection would be seperate systems for each distinct area with different loads, not an economical choice for residential installs . . so we do the best we can

assuming we're in heat mode, all regisers full open, if you limit air flow to the warm room(s), that air will go somewhere . . keep balancing until it ends up in the cold room(s) . .

you could do load calculations, get an air-flow hood, and balance that way . . but the end result will be the same . .

and either way may not be perfect, but at least your getting the best performance out of your equipment . .

if you want to automate a few outlets at this point to achive greater comfort, go for it . . limit (don't cut-off) air to the over-conditioned spaces and it will end up in the under-conditioned spaces . .

Pete:

I appreciate your reply and I understood your caveats.

When speaking to our HVAC contractor he won't even go to the point in acknowledging that there is a problem since he balanced the system. In our house these two rooms are an extreme case where our cold rooms have 3 of six sides seeing outside our unheated garage, while the other bedrooms only see one outside wall. It just doesn't look like this can be balanced out. Exacerbating this is the fact that I think these two rooms suffer a design flaw on his part as the registers are very close to the doors, thus providing a short circuit for the hot air to follow. Further exacerbating the problem is that the cold room is the babies room... very low WAF IYKWIM.

 

[pete]

Pete:

I appreciate your reply and I understood your caveats.

When speaking to our HVAC contractor he won't even go to the point in acknowledging that there is a problem since he balanced the system. In our house these two rooms are an extreme case where our cold rooms have 3 of six sides seeing outside our unheated garage, while the other bedrooms only see one outside wall. It just doesn't look like this can be balanced out. Exacerbating this is the fact that I think these two rooms suffer a design flaw on his part as the registers are very close to the doors, thus providing a short circuit for the hot air to follow. Further exacerbating the problem is that the cold room is the babies room... very low WAF IYKWIM.

Did your HVAC guy design and install your system, or is he just your service contractor? If he did the design he is BSing you, he did not figure enough air for those rooms and/or undersized the ductwork. He should have also installed your registers at the outside wall, instead of saving a few bucks on the duct runs. He owes you a 'properly working system', if your rooms are cold and heating unevenly, it's not working properly.

This is a typical outcome of using "rules of thumb" to design a system, instead of figuring the actual load.

If he is just servicing your system, he may be doing the best he can with what has been installed.

On my residential heating jobs I like to install one register below each window in a room. If I'm doing individual room returns, this usually goes behind the door.

Do you have access the the ductwork? Do you have individual dampers on each supply branch? (duct/flex start collar to each diffuser should have a manual damper (small handle w/ wing nut)). What size ducts serve the cold rooms, and what size are the rooms?

 

[hucker]

Pete:

I appreciate your reply and I understood your caveats.

When speaking to our HVAC contractor he won't even go to the point in acknowledging that there is a problem since he balanced the system. In our house these two rooms are an extreme case where our cold rooms have 3 of six sides seeing outside our unheated garage, while the other bedrooms only see one outside wall. It just doesn't look like this can be balanced out. Exacerbating this is the fact that I think these two rooms suffer a design flaw on his part as the registers are very close to the doors, thus providing a short circuit for the hot air to follow. Further exacerbating the problem is that the cold room is the babies room... very low WAF IYKWIM.

Did your HVAC guy design and install your system, or is he just your service contractor? If he did the design he is BSing you, he did not figure enough air for those rooms and/or undersized the ductwork. He should have also installed your registers at the outside wall, instead of saving a few bucks on the duct runs. He owes you a 'properly working system', if your rooms are cold and heating unevenly, it's not working properly.

This is a typical outcome of using "rules of thumb" to design a system, instead of figuring the actual load.

If he is just servicing your system, he may be doing the best he can with what has been installed.

On my residential heating jobs I like to install one register below each window in a room. If I'm doing individual room returns, this usually goes behind the door.

Do you have access the the ductwork? Do you have individual dampers on each supply branch? (duct/flex start collar to each diffuser should have a manual damper (small handle w/ wing nut)). What size ducts serve the cold rooms, and what size are the rooms?

Pete:

He had control over the whole thing. I know better but I never reviewed the detail design, just the big picture (single zone, furnace location, return locations, basic duct locations). Once I saw it done I asked why the register wasn't on the far side of the room, he hemmed and hawed and said it would balance just fine. I do have access to the duct work so I can fix it. I'll look at the sizing and dampers. It is in the attic on the far side of the house (I have blown in insulation so I want to minimize my access up there. When he was in the entire house was down to studs except the ceiling sheetrock in those two rooms, I am pretty sure he placed these registers so he wouldn't have to crawl 12ft in the attic area.

Thanks...

 

[pete]

Pete:

He had control over the whole thing. I know better but I never reviewed the detail design, just the big picture (single zone, furnace location, return locations, basic duct locations). Once I saw it done I asked why the register wasn't on the far side of the room, he hemmed and hawed and said it would balance just fine. I do have access to the duct work so I can fix it. I'll look at the sizing and dampers. It is in the attic on the far side of the house (I have blown in insulation so I want to minimize my access up there. When he was in the entire house was down to studs except the ceiling sheetrock in those two rooms, I am pretty sure he placed these registers so he wouldn't have to crawl 12ft in the attic area.

Thanks...

many residential installs don't justify a "detail design" drawing . . and the install crew always seems to do things different anyway . . mostly for coordination w/ other trades, but sometimes just because

didn't realize we were talking ceiling diffusers, if they are currently a 4-way blow pattern, you may do better with a 1,2 or 3-way (depends on room size, diffuser location, etc)

if you venture into the attic, and find you do have balancing dampers, confirm those for your cold rooms are full open (blade=handle), and close the damper for your warm room a bit (about 1/4 of the 90deg swing)

also check duct insulation (thickness and fit/finish), at the far end of your duct you may be loosing a bit of heat. You can check air temp at the last diffuser and compare to one closer to the unit.

you might be able to confirm duct size to the diffuser by looking past the blades to see the connection size, or by un-mounting the diffuser . .

(as background info . . what part of the country are you in? (or what country?) most info I give is based on northeast US (when it matters))

(kinda hi-jacked the thread, but still on topic I guess)

 

[CollinR]

On my residential heating jobs I like to install one register below each window in a room. If I'm doing individual room returns, this usually goes behind the door.

In my redneck engineering wisdom I have assumed individual returns and everything on dampers is really the way to go.

This is the only way to strategically pull and push air to areas to balance, or at least I can see no other way.

(kinda hi-jacked the thread, but still on topic I guess)

Keep going! I'm getting a free education on more advanced HVAC concepts.



Also on Rob's attic fan in fire situation, it somewhat hard to say. Obviously if a window/door is open you will feed the fire, if on the other hand you could pull a vacuum the fire would die almost instantly. This is seomthing I have spent much time contemplating at it is completely possible if designed into the house initially. It doesn't take much vacuum for most combustables but the house would need to be designed specifically for it. Lots of issues, windows ane doors are only the start, conventional toliets could overflow many things possibly not considered.

 

[hucker]

what part of the country are you in? (or what country?) most info I give is based on northeast US (when it matters))

Seattle, so our winters aren't that cold. I have thought about adding insulation under the roof to keep the attic a bit warmer and hopefully reducing the heat loss but that is yet another project.... We did blow down to save cost and remove a bunch of soffeting. The current design gives me 100% access to the duct work so that is a 'good thing' when I need to fix it...

 

[pete]

In my redneck engineering wisdom I have assumed individual returns and everything on dampers is really the way to go.

This is the only way to strategically pull and push air to areas to balance, or at least I can see no other way.

Central returns are OK, but need to be planned for. You can get about 100cfm by undercutting the door (30x1 opening at ~500fpm) Or you can use louvers in the bottom of the door, or in the wall above the door (remember transom windows?)

Also on Rob's attic fan in fire situation, it somewhat hard to say. Obviously if a window/door is open you will feed the fire, if on the other hand you could pull a vacuum the fire would die almost instantly. This is seomthing I have spent much time contemplating at it is completely possible if designed into the house initially. It doesn't take much vacuum for most combustables but the house would need to be designed specifically for it. Lots of issues, windows ane doors are only the start, conventional toliets could overflow many things possibly not considered.

I don't think you'll ever put a fire out his way . . plus if you could you'd kill any occupants. Some of the IT rooms I've worked on have 'halon' (iirc) systems which 'starve' a fire . . but if the alarm goes off you have like 30 secs to clear the room before discharge . . if your caught in there it's bye bye time


hucker -

was talking w/ one of the old timers at the shop, he suggested running an additional 6"rd branch to an additional diffuser in your cold rooms (tapping off the main closer to the unit), said he had a similar problem and by the time he balanced as best he could the diffusers were whistling . . just something to consider . .

he also asked me where the thermostat was . . obviously couldn't answer . . but you may want to put it in the baby's room if you can . .

the issue is really that with the heat loss on those 'exposed rooms', even with balanced, even heating, they will cool off quicker than interior rooms . .

and I hate having to suggest it, but a strip of electric baseboard with it's own stat would probably be the best cure for your issue . . (you wouldn't want the main system stat in the room in this case)


Pete C