Uneven air movenmet at heat registers
jh4727
| Posted in Energy, Heating & Insulation on
New two stage variable speed 95% gas furnace installed. The volume of air at each register is signicantly different. At some registers you can barely feel the air, at one register so much air is comming through it whistles.
The contractor came back to balance the system by putting in dampers. Now the registers that barely had air movement are the same and two of the ones that had a lot of air movement barely have air movement, one still whistles, and sounds like a lot of air is moving.
What is wrong with this installation? Is the ducting improperly sized? Should I accept this?
Thank You, JRH
Replies
No.
You need to have this problem fixed, and it may take more than dampers. Installing dampers may not do much to increase air flow at other registers if you have a fundamental problem with duct and plenum sizing.
Installing dampers don't do a thing ,if they are not set properly.How did he balance the system. Did he use the proper air measuring instruments at each grille Did he adjust the cfm/fpm at the Mains?? In other words if he did all this ,then LEAVE IT BE .. (air balancing is almost an art of its own.
On the otherhand if he just went by ear and feel, then I would certainly start complaining to him to get these air quantities in proportion.
The National Comfort Institute, which does a lot of HVAC related training, has a course to certify design and testing of duct systems.
Call around to the HVAC constractors in your area, see if any have gone thru that (or similar courses.)
In my area, there are a significant number of HVAC contractors who haven't, ahhhh, kept up with the times.
The key to forgiving others is to quit focusing on what they did to you, and start focusing on what God did for you. Max Lucado
Sojourners: Christians for Justice and Peace
Where I used to work (at a "desk job") they couldn't seem to balance the system, despite having tried several times. I was told I was not allowed to adjust the air conditioning register above my head. After wearing a jacket and hat and sometimes gloves in summer, I finally took the register down, taped cardboard over the vent and reinstalled the register so it looked like it was open. No one was the wiser, nor was there any difference in the way the system "functioned" (or failed to) for the rest of the workers.
Blocking off one diffuser most times will have hardly any noticeable effect on a system,especialy if there are quite a few others on it, as an office bldg is likely to have.
When the contractor came back and put dampers on two of the registers he said if you put dampers on to many registers it will damage the furnace. Do you know if this is true?
I think the ducting is sized incorrectly. I will be getting back with him in a day or so to have him try a 2nd time to correct the problem.
JRH
I'm beginning to think the reason HVAC people are more secretive about their work than other trades is that they are afraid it might become common knowledge that they don't have a clue what they are doing. ;-)
I have two separate systems in my place and I'm finally after three years starting to get them into balance. In one system I've had to add two booster fans and upsize one duct. In another, I was just about to resize a duct to get more air into the bathroom. When I removed the register, down fell a foam filter which had been blocking half the airflow. That was the only register with a filter, and I suspect the installer put it in to balance the system. But after several years it had clogged enough to severely restrict flow. I also found that another vent hadn't even been hooked up to the duct properly. There was a half inch gap around the register where air was leaking into the attic.
I sometimes even wonder if the real pros know what is going on. Every hospital I've worked in has had horrible air circulation. Sometimes air flow was so bad it would suck papers off the desk or close doors. We had one door that had to be propped open because if closed it would suck everything in the hallway into the room. That same room got worse, and finally we had to remove the air returm cover grate because the whistling sound prevented one from having a conversation. When we got bored, we'd send empty soda cans back to the duct to the physical plant. We made the mistake one day of trying to cover it with a cafetria tray, and the ensuing duct collapse in the ceiling sounded like thunder.
One place put up a new building whose central air duct was so undersized that when running it was impossible to hear in the two adjacent rooms. An engineer for the firm told me that duct speeds were in excess of 100 mph when the system was running. Fifteen years later they are still trying to fix it.
One thing about hydronic, there aren't any ducts to muck up the system.
Wow--talk about horror stories--like the people being sucked out of airplanes, but instead being sucked into ducts! Make a good movie!
Yeah, I like hydronic. Would prefer in slab, but what I've got in this old house, hot water in baseboard registers is okay. I hate forced air.
The HVAC trades, especially sizing, and installing duct systems ,etc is very precise work. Sometimes, the home owner can "undo" what has been done by monkeying with something he has no complete knowledge of.
Then when this happens, its,, "Oh that heating guy..,gee., sob, he buggered up my job"
Get my drift?
Well, I think putting a 3 ft long duct off the plenum with no damper just under the thermostat, and then running the longest duct (with a damper) through the cold air return for about 6 ft qualifies as buggered up.
I'm not sure what your drift is. The system was screwed up and I fixed it, despite my lack of *complete knowledge.* So yes, I do blame the heating guy. What about those other people who aren't able to undue what was done. I guess they just have to live with a few space heaters as we did the first year.
Thank you.
i just put in a 94%varable speed 2 stage furnace. the amount of air movement seems to be much less than a standard furnace, i'm a little coccerned when winter hits but will see...... larry
FWIW, I just attended a combustion analysis seminar where the teacher lambasted the two stage furnaces, arguing that the lower fired stage is extremely inefficient.
I need to note that, although he has pretty much single handedly invented the field of Carbon Monoxide Analysis, he sometime gets questionable concepts lodged in his head, and I don't take everything he claims as necessarily true.
His argument is that in the low firing stage, the flame is relatively narrow and short and the heat radiated to the heat exchanger tubes is significantly reduced by the increased distances. He claims to be able to prove that analysis, but he blew through the proof a bit too quickly for my comfort level to buy completely.
The concept makes sense to me though, so I mention the issue pending further information.The key to forgiving others is to quit focusing on what they did to you, and start focusing on what God did for you. Max Lucado
Sojourners: Christians for Justice and Peace
He might well be right.
But is it wastefull to operate.
A higher percent of the fuel might be lost as waste heat up the flue, but it is a much lower rate of fuel usage that that full fire. So the actuall amount of wasted gas might not be any higher per hour of opeation.
But the low fire will run longer. But what is the waste during the start/stop cycle. With full fire it will run shorter cycles.
Then you need to figure in the "comfort factor".
BTW, in the next year or two I will need to replace my HVAC. I have a furance for the lower level and furnace and AC for the 2nd floor.
When I built in 79 the first "high eff" units where starting to be used. They where spark ignition and motorized dampners on the fuel to stop off cycle drafting. But they seemed to be proned to problems and went with conventional furances. But I think that the AC was a 10 seer, which was high for the time.
So put them in a closed room and used outside combustion air so that it would not draft warmed air. But the because of the construction details the room is not really sealed off and I don't thing that it was as effective as it could have been.
Both units are oversized, but the lower unit is probably 3 times overisze. At zero is still runs less than 1/3 of the time. But because of the heat ducts in the slab there is enough thermomass that the temp does not spike. In fact it holds within 1 degree. But the blower is also way to big and you just can't set near a register in the winter.
When I replace them I want to look at a single FWA with zoning. Because of the two different areas I think that this would probably be a good application for a 2 stage unit.
The other concept that I have is to use a heat pump for the 2nd floor (because it is also airconditionted). Then get a high output WH and use hydro air for the aux heat and also hydro air for the first floor.
Thanks.
Could you explain what you mean by "But is it wastefull to operate."
I assume you left the "?" off. (As someone who has never posted a message with a tyypo I'd like to point out ..... Ah, never mind {G})
And could you explain how the 2 stage units contribute to comfort? I've never quite been able to wrap my mind around that one.
Is it the idea that at low firing, the air being circulated isn't as hot and thus doesn't have quite the same "caught in a Sahara gust of wind" feeling?
BTW, the fellow who teaches the course is a big fan (so to speak) of the 2 stage blowers, just not the 2 stage burners.
>>When I built in 79 the first "high eff" units where starting to be used.
Do you ever see any of the early hi-tech Amana POS's any more?
I just saw a Lennox hot water/air handler unit that looks like a pretty nice concept to me. (Photos attached)
Do you have any insights into them?The key to forgiving others is to quit focusing on what they did to you, and start focusing on what God did for you. Max Lucado
Sojourners: Christians for Justice and Peace
"And could you explain how the 2 stage units contribute to comfort? I've never quite been able to wrap my mind around that one.
Is it the idea that at low firing, the air being circulated isn't as hot and thus doesn't have quite the same "caught in a Sahara gust of wind" feeling?
BTW, the fellow who teaches the course is a big fan (so to speak) of the 2 stage blowers, just not the 2 stage burners. "
This was really an assumption. The assumption that the it would lead to less tempature spiking and thus less running the thermostate up and down to "compensate" and make it worse.
I am not sure how much a 2 sp fan can be used for heating. If you slow it down too much the air will get too hot. I know that good use can be made of it for AC to control humidty removal vs air cooling.
I think that I have heard of variable output gas FWA units that don't have 2 size burners, but rather use duty cycle control (pulse width modulation). That for example will burn for 15 seconds and then off for 30. But I am not sure.
I had heard of the Complete Heat, but never seen one. Basically what I am talking about, but separate units.
And I really don't see any advantages to this unit that would not work as well for separate units.
And I don't see any advantage unless you are trying to do zone, like I am, or maybe a combinated radiant/FWA system.
When I build I had a hard time finding an HVAC contractor that install a system with floor level registers in the first floor. They all looked at the plans and said that they would put a couple of registers in the ceiling for the "basement".
But the "basement" is the main living area and has all of one long wall exposed and more than 3/4's of the 2 side walls. And I knew that it would be cold without floor level heat.
Of course this was all before pex and I was leary of piping in the slab. Not for radiant, but I don't think that I thought about that because it is unknow in this area at that time (and not that common any place). But I just had concerns of broken water piping in the concerete so they are all between floors.
About a month before I started I got the idea of using electric radiant heat in the floor as supplimental and then go with one system with ceiling registers.
But I did not have time to really investigate.
If was building it today most likely I would go with with hydro radaint in the first floor and FWA (probably via hydro air) for the 2nd floor.
>>the amount of air movement seems to be much less than a standard furnace,
Furnaces come with different settings for blower speed and adjustments: some heating contractors and installers don't necessarily get the right settings selected.The key to forgiving others is to quit focusing on what they did to you, and start focusing on what God did for you. Max Lucado
Sojourners: Christians for Justice and Peace