Any Harm In Increasing The Control Limit Temp Value? - HVAC - Page 2 - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 01-16-2013, 12:47 AM   #16
I'm Your Huckleberry
 
Join Date: Mar 2011
Posts: 5,884
Rewards Points: 2,220
Default

Any harm in increasing the control limit temp value?


Absolutely zero possibility of that duct being from any earlier than the late 1990's. Even the plenum and collars are all clearly new-ish.

The key thing which you touched base on previously was air flow being "restrictive". It appears that that is no where near a professional install if that duct work is how it was when you bought the house, how it currently is and I'm not talking about them just thrown all about but mainly due to insulation not being pulled up over the collar and panduit strapped as well as there being no sealing of the duct collars to the plenum. There is also no seal from the furnace/evap to the plenum. It looks, it is, incomplete.

I'd say seal that first and then worry about your high limit but it leaking air is probably keeping it a bit cooler.

Manometer: test air flow/static pressure across the system FIRST!!! I'm betting your static pressure is very high as in no air flow as in hot air collecting internally of the furnace and thus overheating the limit. And again, that's with the air leaks. Pretty much your system is choking on it's own breath or at least that's how I'm seeing it from this end.

Move the air properly and the system will be fine. That being said you'd need to determine if the duct sizes, both return and supply as well as the return air grill, are adequate to move the required cfm for your system. Then you can worry about design and layout of the ducts as well as getting to fixing the dozen or so air leaks that system has.

post the make and model number of your furnace and someone can find the manual or call the manufacturer and find out what the limit is supposed to be but never change the design temp of a limit.

Advertisement

__________________
Thanks.
Doc Holliday is offline   Reply With Quote
The Following User Says Thank You to Doc Holliday For This Useful Post:
COLDIRON (01-16-2013)
Old 01-16-2013, 06:19 AM   #17
Member
 
Join Date: Mar 2010
Location: PENNSYLVANIA
Posts: 2,258
Rewards Points: 1,044
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by YKdave View Post
Wow, thats quite the octopus goin on there LOL

anyways, lowering the output is a definite option, but that also comes at the cost of reducing efficiency. every heat exchanger has a specific BTU and airflow where it is its most efficient. too much fire and your blowing it all out the flue (and burning up the heat exchanger), same goes for airflow across the heat exchanger, too low of airflow and heat exchanger temp gets too high (heat out the flue and burning it up!) and as backwards as it sounds, too much airflow across the heat exchanger reduces efficiency as the exchanger cannot transfer the heat to the air at a fast enough rate

The biggest thing you need to do, is measure your return air temp and compare that to your hot air (getting a flue temp wouldnt hurt). Your furnace is rated for XXX* heat rise, which you are likely exceeding greatly. you need to either adjust the firing rate (BTU) or airflow to get the heat rise within spec.

Where is the air return ducted? is it possible that this unit is sucking in a fairly high temp return air which would cause the excessive heat?
" Are you the same guy that was asking all the questions about your trailer heat?
__________________
No Warranty Means- If it breaks in half you get to keep both halves.
COLDIRON is offline   Reply With Quote
Old 01-16-2013, 07:02 AM   #18
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,463
Rewards Points: 4,572
Default

Any harm in increasing the control limit temp value?


Post brand and model number of that furnace.

You can't get an accurate temp reading in that plenum, as any probe would see IR heat and read a much higher temp.

Post what size those 2 ducts are, and what size return it has. From what little can be seen in those pics. You don't have nearly enough air flow for even a 45,000 BTU 80% furnace.
beenthere is online now   Reply With Quote
Old 01-16-2013, 09:45 AM   #19
Newbie
 
Join Date: Jan 2013
Location: Boston, MA
Posts: 14
Rewards Points: 10
Default

Any harm in increasing the control limit temp value?


Wow thanks everyone for the flood of input!

I’m kicking myself for not measuring the SIZE of the ducts. The return air duct comes in from the right side and is quite large, probably a 12” wide circle. The outputs are probably roughly 6” in diameter but I’ll confirm both as well as the make and model.

I know it’s a Conquest 80 but I’m not sure which model it is.
http://www.groomsappliance.com/pdf/comfortfurnce80.pdf

Regarding the duct work, what’s shown in the photo is all the new stuff they put in when they must have installed the furnace. Under all the pink insulation is the original, OLD duct work that might be original with the house or just plain old. The reason I think the duct work is original is because upstairs all the registers are old cast iron grates. Yes, the workmanship is horrible. Every time either system turns on all the ductwork buckles and pops with the increase of pressure and makes all kinds of horrible noises, I've been strapping/supporting sections to prevent the noise. There are also definitely leaks everywhere.

I will see if I can borrow or buy a manometer, that will tell an interesting story I’m sure.

That is a VERY good point about the IR, I will get a temperature reading in the return air plenum and the outlet from the heat chamber (out of line of sight of the heat exchangers).

I will get the model and temp info tonight and hopefully some pressure measurements.
CzarDestructo is offline   Reply With Quote
Old 01-16-2013, 10:41 AM   #20
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Rewards Points: 500
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by beenthere View Post
Post brand and model number of that furnace.

You can't get an accurate temp reading in that plenum, as any probe would see IR heat and read a much higher temp.

Post what size those 2 ducts are, and what size return it has. From what little can be seen in those pics. You don't have nearly enough air flow for even a 45,000 BTU 80% furnace.
This is probably the most accurate statement concerning your over temp prob, Czardestructo.

Your duct lay out is a tangle of twists and turns and that causes a slow done in your airflow and causes the temp to raise and open the limit.

To get a Delta T off that beast I would have to take multiple reading and use my best educated guess.

But right now that is not even the most pressing problem. That duct work would have to be re-done to make it right and get the Delta T in line with specs.

Surprised the hat exchanger is still intact.

On you still having the old iron grates let in the living area, that's something a lot of old gravity installs had in common. Most HOs would not want to have to redo them of aesthetic reasons.
hvac5646 is offline   Reply With Quote
Old 01-16-2013, 02:03 PM   #21
Newbie
 
Join Date: Jan 2013
Posts: 10
Rewards Points: 10
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by COLDIRON View Post
" Are you the same guy that was asking all the questions about your trailer heat?
Are you the guy that replied with telling me to run an oudoor unit that would be completely unpractical in our climate?
YKdave is offline   Reply With Quote
Old 01-16-2013, 05:10 PM   #22
Newbie
 
Join Date: Jan 2013
Location: Boston, MA
Posts: 14
Rewards Points: 10
Default

Any harm in increasing the control limit temp value?


70F delta before the furnace shuts down, 130F air coming through one of the outlets, 58F return. I've got problems.

Unit is a HCI model# gmuh75-e4n. It was built in 2003 so apparently it's not that old! 75,000BTU, 80% efficient.

The return air duct is a circular 12" duct, two outlets are 8" circular ducts but one turns into a square duct once it enters the structure. The circular duct is just sort of stuffed in there and leaks a LOT of air. It might have made sense when it was gravity fed but now its just a leaky mess.

It would appear I need a professional to just redo this disaster but I'm going to bet its going to entail breaking into some walls and a lot of money...


Right side of the furnace

Last edited by CzarDestructo; 01-16-2013 at 05:15 PM. Reason: smaller photo, first was too big!
CzarDestructo is offline   Reply With Quote
Old 01-16-2013, 06:22 PM   #23
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,463
Rewards Points: 4,572
Default

Any harm in increasing the control limit temp value?


Even that return duct is too small.

The furnace is probably also to big for the load its handling.
beenthere is online now   Reply With Quote
Old 01-16-2013, 08:38 PM   #24
Newbie
 
Join Date: Jan 2013
Location: Boston, MA
Posts: 14
Rewards Points: 10
Default

Any harm in increasing the control limit temp value?


Load meaning the size of the unit it's heating? Is 75,000BTUs too much for about 1700 sq ft across two floors?
CzarDestructo is offline   Reply With Quote
Old 01-16-2013, 09:08 PM   #25
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,463
Rewards Points: 4,572
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by CzarDestructo View Post
Load meaning the size of the unit it's heating? Is 75,000BTUs too much for about 1700 sq ft across two floors?
There is a chance that a 45,000 or 50,000 BTU would be big enough.
beenthere is online now   Reply With Quote
Old 01-17-2013, 07:49 AM   #26
Newbie
 
Join Date: Jan 2013
Location: Boston, MA
Posts: 14
Rewards Points: 10
Default

Any harm in increasing the control limit temp value?


Well then the fact that the other furnace is ALSO 75,000 BTUs and is only heating a 600sq ft apartment is fairly amusing...
CzarDestructo is offline   Reply With Quote
Old 01-17-2013, 08:04 AM   #27
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,463
Rewards Points: 4,572
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by CzarDestructo View Post
Well then the fact that the other furnace is ALSO 75,000 BTUs and is only heating a 600sq ft apartment is fairly amusing...
That is sad. It should have the smallest furnace you can find. Which would be a 40,000 BTU input. And even that would be over sized. But at least it would have a few minutes to get up to its steady state efficiency.

You did say apartment right, not a greenhouse. A 600 sq ft greenhouse would take a lot of heat.
beenthere is online now   Reply With Quote
Old 01-17-2013, 11:50 AM   #28
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Rewards Points: 500
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by beenthere View Post
That is sad. It should have the smallest furnace you can find. Which would be a 40,000 BTU input. And even that would be over sized. But at least it would have a few minutes to get up to its steady state efficiency.

You did say apartment right, not a greenhouse. A 600 sq ft greenhouse would take a lot of heat.
OP did say it was a 1900s house. It could be leaky as all get out. Also most 1900s homes I have seen have big windows and even with with new windows it would still require more heat than a modern 1700 sq ft ranch.
hvac5646 is offline   Reply With Quote
Old 01-17-2013, 12:01 PM   #29
Part of the Clover Leaf
 
Join Date: May 2011
Location: NW Burbs of Detroit Mi.
Posts: 1,107
Rewards Points: 500
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by CzarDestructo View Post
70F delta before the furnace shuts down, 130F air coming through one of the outlets, 58F return. I've got problems.

Unit is a HCI model# gmuh75-e4n. It was built in 2003 so apparently it's not that old! 75,000BTU, 80% efficient.

The return air duct is a circular 12" duct, two outlets are 8" circular ducts but one turns into a square duct once it enters the structure. The circular duct is just sort of stuffed in there and leaks a LOT of air. It might have made sense when it was gravity fed but now its just a leaky mess.

It would appear I need a professional to just redo this disaster but I'm going to bet its going to entail breaking into some walls and a lot of money...


Right side of the furnace
At 58* f return air I would say you are sucking cold air from basement.

Your supply temp is not reliable with out taking other out let temps. I have to say to draw and fairly accurate conclusion you'd need some experience in the HVAC field .

Not to take anything away from you, but in this case KNOWLEDGE IS NOT EXPERIENCE...but I think you will probably keep at til you get it or ..well you get what I mean.
hvac5646 is offline   Reply With Quote
Old 01-17-2013, 01:28 PM   #30
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,463
Rewards Points: 4,572
Default

Any harm in increasing the control limit temp value?


Quote:
Originally Posted by hvac5646 View Post
OP did say it was a 1900s house. It could be leaky as all get out. Also most 1900s homes I have seen have big windows and even with with new windows it would still require more heat than a modern 1700 sq ft ranch.
The 600 sq ft apartment probably doesn't need anywhere close to 100 BTUs output per sq ft.

1700 sq ft 2 story, maybe a 60,000 BTU input 80% on extreme cold nights.

I do 2400 sq ft 2 story 1930s with 70,000 90%ers, and they have room to spare at -6 outdoor temp.

The OP would need to do a load calc to find out for sure what size his home needs. But he isn't getting the full output from his furnace.

Advertisement

beenthere is online now   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Remove Mixet Temp Control Handle mixet Plumbing 1 09-01-2009 10:55 PM
Limit control switch help farnsworth6406 HVAC 8 01-13-2009 12:40 PM
fan limit control question sbriggs_1 HVAC 2 12-11-2008 08:09 AM
Wiring limit control on gas boiler uncleneiler HVAC 2 11-21-2008 02:54 PM
Wiring limit control on gas boiler uncleneiler Electrical 1 11-21-2008 09:03 AM




Top of Page | View New Posts