I had a room addition several years ago and in turn I had my HVAC modified for the addition. Since then it's been totally screwed up. Basically I have a VSAH that's pushing 1800 cfm air flow through a 8 X 16 main truck duct that is 54' long that has 19 6" round ducts off the trunk. In addition there are 3 boxed 90 degree turns in the duct before it even gets to the first take-off duct. My NEW HVAC contractor is working to get the system back to spec. In the last couple of weeks he has resized my return ductwork, (it was undersized also) and will start on the supply side shortly. With the AH running he tried to remove the door from the the furnace blower and the suction inside the AH was so great it wouldn't come off, we had to shut the furnace off to remove the door. He said he has never seen one with that much suction before. Is this a sign that the return air ductwork is still too small? What else could be causing this?
Also it seems, according to the contractor, that my heat pump is oversized. What is happening is that the air gets too cold and kicks out the heat pump on AC. So the heat pump runs about 3 minutes then shuts off for 5 minutes when it kicks out. This, with the addition of undersized ductwork, is preventing the house from cooling off. He disconnected the thermostat probe so that it does not read the air temperature and does not kick out the heat pump. He says he never installs the probes in his system and it's not needed. Will this cause a problem?
After getting ripped off so bad by my first HVAC guy I'm kind of leary about this guy now.
At some point you're going to have to find someone you can trust. From what I can see its a nightmare system and if its really moving that kind of air through that duct you have a noise problem too. You may consider contracting a company that specializes in design and build. Tell them your problem and dont start the conversation off with anything that implies you are looking for a quick or cheap fix because that is just what you'll get. Obviously we can not see this from here so you definately need to consult a good strong contractor and plan on speding a few denero if it needs it.
Not being able to pull the blower door off is kind of an obvious sign that the return is too small. I suppose there could be other explanations. But I'm not sure what. Residual insulation glue on the door maybe? Nah.
The unit may be oversized or it may just be that your zone system is crap like most are. This may be useful. This should depress you. And I only skim the subject. I don't mention the fact that heat pumps in particular really don't like being zoned in heating mode. In heating mode the air handler's coil becomes the compressor's radiator. Cut off a lot of the airflow to any radiator and what happens? Things overheat. Now supposedly the variable speed air blower will compensate for this. But if that were true he wouldn't have needed to pull the duct sensor. That sensor is there for a VERY good reason. It protects your equipment from overheating in winter and freezing in summer.
I'm going out on a limb here. But that guy that yanked the sensor and said he never installs them is a schmuck of the highest order. You can't buy that kind of stupidity. It's a gift from Satan himself. Like doc said. Find yourself a real pro. It's tough but they're out there. Unfortunately you often trip over several idiots on your way to finding them.
I agree, pulling out the temp. sensing probe is not a solution to your problem. You are asking for trouble in the way of a frozen coil or overheated unit by doing this. Cold medication doesn't get rid of your cold it only masks the symptoms, works the same way when you bypass or remove a safety. Condition is stilled there, it just isn't sensed by the unit.
[Edited by Black Adder on 06-17-2005 at 04:26 AM]
"Go big or Go Home"
19 supplies coming off 16x8 duct wow did your baby sister install the system
Ducts sound severely undersized.
Manual J,then S,then D all from ACCA ,to get the right size system and ducts.
Have you ever been outside at the airport and heard a 777 take off, you get about the same effect in my basement.
There are 2 Lennox dealers within about 50 miles of my house and this guy is the one everyone recommends, go figure. He wants to run the tests to size my supply system correctly, but he has already said he will have to take out the zoning controls to balance it. I paid big bucks for that and don't really want to lose it. Especially when one of the zones is a large master bedroom, (800 ft/2) that has no business on in the daytime. Of course the guy who installed the system lost his Lennox dealership and the local union is sueing him.
As far as the excess negative pressure in my VSAH, if I understand A VSAH correctly it keeps increasing RPM's until it reaches the CFM's that it's set at. I have an EAC that has a prefilter and post filter plus I have been using a red Filtrete paper filter after the EAC, maybe all the filters are starving the blower for air and it's increasing RPM's to reach its setpoint which compounds the problem.
I appreciate the help.
Originally posted by frank_m
I have an EAC that has a prefilter and post filter plus I have been using a red Filtrete paper filter after the EAC, maybe all the filters are starving the blower for air and it's increasing RPM's to reach its setpoint which compounds the problem.
NEW Definition of ...
1. Get rid of the filters.
2. Essentially the discharge air flow must be divided into TWO major Supply Air paths ( + follow ZONING plan).
ADD A 2nd main header that is 10" x 16" which will handle total of 1000 CFM.
Existing 8" x16" will handle about 800 CFM if the 90 degree elbows are modified to MITERED elbows.
Each 6" diameter supply duct will handle about 100 CFM each.
Master bedroom ( 800 Sq. feet) may need ~ FIVE 6" diameter supply outlets.
It's Not Rocket Science, But It is SCIENCE
with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
EAC and prefilter,only,you'll feel the difference in air flow.
Thanks for the info Dan, actually what you said I suggested to my contractor at the very beginning, I think I even made a post on this forum a month or two ago asking if it would work. He doesn't like it because the zoning is not removed. He said he would do it if that's what I want. The new addition, the bedroom, is not a problem my contractor said it's duct sizing is okay, although I don't understand how a 5 ton heat pump dumping into a 800 ft/2 room is okay. It's the original house where the original guy tried to tie the new system into my old ductwork that's bad. I should post some pictures of this mess in the wall of shame.
My AH is in the garage, the supply takes a 90 at the plenum and goes into the basement, it then takes another 90 and runs across the width of the house, then takes another 90 to align it with the existing 50+ feet of 8 X 16 ductwork. What I suggested is before the second 90, that takes it across the width of the house, he run a duct straight out, basically making the trunk a "Tee", putting half the registers on the new duct and leave the other half remaining on the original duct. Then putting dampers on all the take-offs.
As far as all the filters, I put the filtrete in to check to make sure the EAC was working and just forgot to take it out. The pre and post filters came with the EAC. I took Dash's advice and removed the 2 after the EAC.
Is that duct with the 90° elbows also 8X16,or larger?
If larger adding some turning vanes would help .
Two are 8" X 20" and the 3rd is where the 8" X 20" meets the 8" X 16", this one is just a 90 degree angle, no radius.