HVAC

Have HVAC Questions? Ask an HVAC Expert for Answers

Ask an Expert,
Get an Answer ASAP!

HVAC
This answer was rated:

I installed an 80% gas furnace in a house with foam insulation

I installed an 80% gas...
I installed an 80% gas furnace in a house with foam insulation on walls and under roof. So the envelope includes the attic. An engineer has suggested that I should have installed a 90% furnace with a sealed combustion system ( I have a 4" duct feeding fresh outside air to the combustion chamber and 4" double wall flue pipe). He says the attic should be totally sealed from infiltration.
To me, this is a tiny amount of infiltration to cause me to have to replace the furnace.
Show More
Show Less
Ask Your Own HVAC Question
Answered in 1 minute by:
6/3/2011
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,151
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Phil :

Hi,This is risky business, not responsible for damages on your end. We *keep going until *you are happy. I come and go. be patient

Phil :

You are correct, IF the flue goes out through the roof... insulation is irrelevant in that case.

Phil :

tell me what you think he saw to have reason to give you that advice. maybe i am missing something.

Phil :

we can go from there, Phil

Customer:

The end user (homeowner) is having difficulties maintaining comfort level in the upstairs area where this furnace is installed. He is looking for things that would cause excessive heat to get into the conditioned area.

Phil :

The furnace wont contribute to that.

Phil :

but with an insulated roof, the attic and the second floor should run about the same temperature as the first floor with the same size cooling system installed, and equal duct sizes, and no kinked ducts, and no air diffusers shut off.

Phil :

Tell me the square footage of the home, and the type of construction, and city..and btu or tonnage rating of the outside condensing unit.

Phil :

we can go from there. Phil

Customer:

Its just the fact that foam is used to insulate a house because it is good at reducing infiltration of outside air that gets through fiberglass insulation in walls and ceilings, yet here i am, furnace installer, adding outside air to the attic. It bothers me to not have some fresh air in the attic space where the outgassing from the foam will build up over time/

Customer:

This house has 2700 s.f. of conditioned space upstairs with a 4 ton 15 SEER condenser and evaporator,and 5600 s f. downstairs on three 2.5 ton15 SEER systems downstairs. The house is outside the city next to a huge lake.

Customer:

The outside walls are rock with wallboard inside and composition roof.

Phil :

Thanks, XXXXX XXXXX of AC... my guess is that the units are over charged by a few ounces each...the suction pressures should run at 32F equivalent pressure off the chart for the the refrigerant used

Phil :

Lately I see techs not well trained in this, over charging systems

Phil :

Tell me what refrigerants are being used (its on the outside unit model number labels as an R number, such as R-22 or R 410a etc

Phil :

I will give you the proper suction pressures.

Phil :

Phil

Phil :

I might not b back until the AM.. its late here.

Phil :

Phil

Customer:

It's R410A.

Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,151
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified
Phil and 87 other HVAC Specialists are ready to help you
Ask your own question now
Customer reply replied 6 years ago
I still need help getting through this, but do not know haw to get back with you. Will try again tomorrow.
http://www51.honeywell.com/sm/genetron/common/documents/technical-documents/Genetron-AZ20-R22-Pressure-Temperature-Chart.pdf

charge to suction pressure of 100 psig to 102 psig max
98 psig will be most efficent though, but might result in a tendenct to ice the coils.

if this does it for you, plase click the big green accept button next to this question, thats how i get paid

Thanks!
Phil
Ask Your Own HVAC Question
Customer reply replied 6 years ago

That makes sense, you want the coil as cold as possible without freezing up. When it was checked, recently, the suction pressure was in the range you specified and the TD across the coil was 16. Currently, my primary issue with this engineer is that he told the homeowner that the systems should have sealed combustion furnaces in a foam insulated house, but I was originally advised against this due to condensation during the heating season mixed with a cold attic that could produce mold in the attic.

A forced draft furnace would not produce condensation, it would burn it off. The current opinion of others at this point, for the difficulty the system is having in keeping the area cool, is the envelope includes the attic with no insulation barrier between the living space and attic. The attic space is quite large. All the other foam houses I have worked on have had little or no attic space.

Hello again, as long as the furnace is vented to the outside.... and has its own air intake from the outside via plastic vent and intakes as with true sealed systems there will be no condensation in the attic.

a forced draft furnace still *must be vented to the outside, and still must have outside air intake vent from the outside

condensation is not an issue in any of these cases.

if the furnace exhaust were vented illegally to the attic.. then you would have condensation and a very very dangerous installation for carbon monoxide poisoning of the occupants.




If the furnace has only an exhaust vent, as with most high efficiency furnaces, its not a true sealed system and air intake from outside into the attic must be provided.

Leaving the top floor ceiling exposed to cooler air in the *winter, and only slightly warmer air in the summer due to the relatively small make up air opening required by law in that case will put a bit more load into the top floor rooms... in any event this would not be your problem.. its an engineering issue.

the engineer, not you, might owe the home owner 2 or 3 inches of insulation over the bottom of the attic space.

the Ruud unit specified by the way is not a sealed furnace by any stretch, so it must have outside air, and it *must be vented through the roof as you most likely have done.
refer to the furnace installation instructions.

http://www.acdirect.com/xcart/product.php?productid=366
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,151
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified
Phil and 87 other HVAC Specialists are ready to help you
Ask your own question now
Ask Phil Your Own Question
Phil
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,151
9,151 Satisfied Customers
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial

Phil is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future.

JimmyBagley, IA

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

< Previous | Next >

Meet the Experts:

Phil

Phil

Mechanical Engineer

9,151 satisfied customers

Retired HVAC/ Electrical & Boiler contractor. Industrial

Rick Mather

Rick Mather

HVAC Technician

3,133 satisfied customers

35 years experience, HVAC

Matthew

Matthew

HVAC Technician

2,014 satisfied customers

14 years experience in the HVAC field of service, installation, Manual J & D calculations

Kenton Guidry

Kenton Guidry

HVAC Technician

963 satisfied customers

12 years install/service experience.

Brian HVAC Guy

Brian HVAC Guy

HVAC Technician

953 satisfied customers

I have been an HVAC/R mechanic/technician for 30+ years.

Rick Ridley

Rick Ridley

UK Heating Engineer

871 satisfied customers

Retired But have had 30 years on the tools, Ex CORGI

Tom

Tom

HVAC Technician

770 satisfied customers

16+yrs HVAC/R service. Residential Commerical Industrial

< Previous | Next >

Related HVAC Questions
If light on a Rheem 90 high efficiency furnace is blinking
If green light on a Rheem 90 high efficiency furnace is blinking twice, how do you know if the high pressure or low pressure switch is faulty? … read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
I have a question about Carrier High Efficiency furnace,
I have a question about Carrier High Efficiency furnace, this thing is driving me crazy. The problem with it is it will stop working in the night. This is a Furnace/AC and Dehumidifer all in one model… read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
What causes a Rheem GRA- GRJ furnace exhaust to frost up? We
What causes a Rheem GRA- GRJ furnace exhaust to frost up? … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
My high efficiency furnace has stopped working normally. I
My high efficiency furnace has stopped working normally. I have discovered that the main burner will only ignite and burn when the pvc vent from the outside is lifted from its seat so that the combust… read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
Does it make sense that the outside condenser unit for the
Does it make sense that the outside condenser unit for the second story of our split HVAC system is 3.5 ton but the evaporator unit in the attic is 4 ton?… read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
I have a payne furnace.. installed this summer..it's not
I have a payne furnace.. installed this summer..it's not coming on when it should. Thermostat shows unit is on but temp keeps dropping … read more
HVAC Guru
HVAC Guru
Service Technician
Associate Degree
682 satisfied customers
Natural gas furnace exhaust vent has a strong propane ordor.
natural gas furnace exhaust vent has a strong propane ordor. nothing is smelled inside the house … read more
Gaztech
Gaztech
Technician
Vocational, Technical or Trade School
1,142 satisfied customers
I have a Ducane high efficiency furnace and the draft
Hi I have a Ducane high efficiency furnace and the draft inducer fan will not go on. It just hums. I also have no LED light blinking at all. … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
Have a weather maker infinity ultra high efficiency furnace
have a weather maker infinity ultra high efficiency furnace 1/2 hp electric motor kgmp 2001all fan seperated from shaft disk fan 9 inchs in diameter … read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
Question about basement insulation... It's not a problem -
It's not a problem - it's a question...we live in the Atlanta area. 3 years ago, we purchased an existing home that has a full, unfinished walk-out basement, which means that the entire north and west side of the basement is above grade. The south and east walls are poured concrete and are below grade. When we bought the home, it had zero insulation in the stud walls on the north and west sides. The concrete walls also were not insulated. However, there was faced fiberglass insulation stuffed between the floor joists in the basement ceiliing … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
Have a 90 Plus high efficiency furnace with error code 31.
Have a Bryant 90 Plus high efficiency furnace with error code 31. Yearly I seem to get this due to birds building nest in the intake. I the use shop vac to clear it out and I am back in business. Howe… read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
New r410 condensing unit and new evaporator coil. gauges go
new r410 condensing unit and new evaporator coil. gauges go straight to retard when unit starts … read more
Airheatman
Airheatman
Heating & Air Conditioning Contractor
6 years college
1,836 satisfied customers
I have a lennox high efficiency furnace, it's not blowing
I have a lennox high efficiency furnace, it's not blowing hot air … read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
My high efficiency furnace is showing 3 flashes on the code
My coleman high efficiency furnace is showing 3 flashes on the code - says pressure switch stuck open - which switch is that? … read more
Rick the plumber
Rick the plumber
Owner
9,857 satisfied customers
Have trouble with unit suction pressure rise but discharge
Have trouble with unit suction pressure rise but discharge don't … read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
Rheem Model number RCFA – HM3617AC, Suction pressure 68
Suction pressure 68 discharge pressure 92 why is my discharge pressure low. Outside temperature around 85 . … read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
I recently had a goodman high efficiency furnace installed.
I recently had a goodman high efficiency furnace installed. The pvc intake and exhaust where run up a preexisting chimney to the roof. The pvc intake and exhaust are touching side by side with no spac… read more
Tim Ohms
Tim Ohms
HVAC Journeyman
31 satisfied customers
Sx ultra 80 high efficiency furnace. installed new
sx ultra 80 high efficiency furnace . installed new thermostat and outside ac unit wont come on, only inside blower. i read some on this forum and twisted the red blue and green together with no therm… read more
Phil
Phil
Mechanical Engineer
9,151 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x