[janralix]

I have a 2,200 s.f. house, all on one level, over a basement/garage. The basement/garage is not heated or cooled. Excellent ducting is already in place, as per an HVAC pro who inspected the house. No new ducting, outlets, or returns will be necessary. I only need to replace an old natural gas furnace & air conditioning unit with a heat pump (I'm in East Tennessee). I was told I needed a 4 ton unit at a cost of about $10,000. This seemed excessive to me. My house is brick & I do have large windows. Any thoughts? Thanks.

 

[zootjeff]

I have a 2,200 s.f. house, all on one level, over a basement/garage. The basement/garage is not heated or cooled. Excellent ducting is already in place, as per an HVAC pro who inspected the house. No new ducting, outlets, or returns will be necessary. I only need to replace an old natural gas furnace & air conditioning unit with a heat pump (I'm in East Tennessee). I was told I needed a 4 ton unit at a cost of about $10,000. This seemed excessive to me. My house is brick & I do have large windows. Any thoughts? Thanks.

Are you interested in doing it yourself? Do you trust the 4 TON number?

I'm into a 2.5 Ton heat pump system for about 2000 in parts (Everything but brazing wire) and I'm doing it myself.

The 4 ton system is about 500 dollars more then that from the place I used.

You could probably do it yourself for under 3000 assuming you paid someone 500 to do setup and inspection..

-Jeff

 

[Home Air Direct]

I have a 2,200 s.f. house, all on one level, over a basement/garage. The basement/garage is not heated or cooled. Excellent ducting is already in place, as per an HVAC pro who inspected the house. No new ducting, outlets, or returns will be necessary. I only need to replace an old natural gas furnace & air conditioning unit with a heat pump (I'm in East Tennessee). I was told I needed a 4 ton unit at a cost of about $10,000. This seemed excessive to me. My house is brick & I do have large windows. Any thoughts? Thanks.

I ran a simple block load on your home, using Knoxville as the Long/Lat, and took liberties to create a lot of windows and very weak insulation factors and loose construction. All of this is a SWAG at this point, but it points to the fact that 4 tons is most likely to large for your area and size. I came up with about 36,000 btu of total cooling needs and about 63,000 btu of total heat.

All of this is a guess until you give specific information and receive an accurate load calculation, but I was very liberal regarding your windows and insulation and my uninformed calc would say that 4 tons is big overkill.

Are you planning on going Dual-Fuel and end up with a gas furnace/heat pump combo. If it were me, that would be my route. And don't be wowed by ultra high efficiency equipment. the best bang for your buck, considering the age and overall efficiency of your home, both in utility and investment would be a high quality (read, not builder grade) 13 SEER Heat pump and an 80% gas furnace as a back-up heat source. Just my $.02 And, $10K is way on the high end of a change-out.

Good luck with your project.

 

[beenthere]

Just my $.02 And, $10K is way on the high end of a change-out.

Good luck with your project.

Unless it was a 2 stage unit.
And that price included upgrade of electrical service to handle electric aux heat.

 

[Home Air Direct]

Janralix, Do you know your insulation factors (R) of your walls and ceiling? You would be surprised at what adding overhead insulation will do for your load requirements. Also, are your windows single or double pane?

 

[Yoyizit]

And I got ~1.3 therms heat loss, using 6 BTU/sq.ft./HDD.
You should go with the 0.63 therms.

 

[Home Air Direct]

And I got ~1.3 therms heat loss, using 6 BTU/sq.ft./HDD.
You should go with the 0.63 therms.

Can you dumb that down for me and elaborate on how you are coming up with the therms and who you relate that to this 2200 sq ft in E. TN?

Thanks. I am interested.

 

[Yoyizit]

Can you dumb that down for me and elaborate on how you are coming up with the therms and who you relate that to this 2200 sq ft in E. TN?

Thanks. I am interested.

Got the HDD for Knoxville from
http://www.degreedays.net/

Here's an example calc.

victoria, BC
So 750 gals of oil giving 1100 therms for 4900 HDD for 180 days for 2000 sq. ft.
6.1 therms/day
2000 sq. ft gives 6.1/2000 = 305 BTU/day/sq.ft.
4900/180 = 27 HDD in one day
305/27 = 11 BTU/sq. ft./HDD
Effic. factor 0.8
final 8.8

Here's some people who use this
http://www.focusonenergy.com/files/Document_Management_System/Evaluation/weshbillingstudy_report.pdf

my samples, from forums, ranked
1.7 least heat loss
3.8
4.0
4.4
5.7
8.0 - my 40 yr old house
8.8
11 most heat loss

Histogram
0 to <3|x
3 to <6|xxxx
6 to <9|xx
9to<12|x

An old magazine I inherited confirmed the 6 BTU/sq.ft./HDD average loss but he didn't cite references.

The Law of Large Numbers may say that the more samples I get the less accurate each has to be.

From what you posted, I should be the one asking you questions!
And here's my first question, with Carrier's answer.
"What is Block Load ?
Carrier's Block Load program is a powerful, fully featured HVAC load estimating program suitable for commercial buildings of any size."

 

[Home Air Direct]

From what you posted, I should be the one asking you questions!
And here's my first question, with Carrier's answer.
"What is Block Load ?
Carrier's Block Load program is a powerful, fully featured HVAC load estimating program suitable for commercial buildings of any size."

First off, your analysis makes my head want to explode:huh: What secret underground lab do you work in:laughing: You have some very intense math a goin on in your head.

Block Load: For me it is a starting point until additional information can be gathered. I am using Carrier's Rezcalc (block load) and am basically using the extremely small amount of information that I have, geographic area, sq ft and anything else that is given, along with assumptions that fall on the liberal side for insulation or lack thereof and construction that is usually on the loose side to average. This gives a base range for heat/cool load, until additional correct info can be add to narrow down the btu's needed.

Almost every block load I run, shows total cooling well below all the rules of thumb, and many times below local contractors recommendations. it took me a long time to trust this, but it has only failed me once (locally) and in the end was discovered that the insulations and sq ft that I was given were not as originally spec'd.

 

[Yoyizit]

What secret underground lab do you work in:laughing:

Actually it's high in the snow-covered mountains of New York's Central Park.:laughing:

One weak point with my method is the efficiency multiplier. It's 100% for elec. heat, but what about an 83%-nameplate- efficiency-rating, oversized gas furnace that is only on 1/4th of the time in winter? So my heat losses are probably overstated, in this case possibly by a factor of ~2.

When I had a Manual J from my local library I should have done the calc. on my own house, but it was just too tedious.

I'd trust your method. Your software is designed by experts, in HVAC and numerical methods.

 

[Home Air Direct]

"What is Block Load ?

I just realized that I did not answer your question.

The block load that I use is just a simple Manual J that only takes into account the mass structure and not the individual rooms and their loads.

 

[sweaty]

I would seal and insulate the attic and basement/garage as thoroughly as possible first. You'll then be able to get a smaller heat pump and easily heat/cool it. Get a variable speed heat pump. You'll save a LOT of money in the long run.

 

[beenthere]

HHD to determine load is inaccurate.

There are enoguh low cost DIY load calc programs, here is no reason to guess.
Or use rules of thumb.

 

[tk03]

For more info on why do a heat loss calculation see the following link.
http://www.comfort-calc.net/faq.html
My house was built in 1978 and is about 2800 sq ft of living area. I live in south central PA and my heat loss is about 40k. May heatpump is 3 ton with 10K of electric backup. I have one bank of the electric disconnected. The home still heated OK at 2º OD temps last winter.
Doing my heating degree days my HDD comes out to 1.9 btu's per sq ft. That is a far cry from 6 HDD's per sq ft.

 

[gsistore]

Hi there, a Payne 4 ton heat pump system runs about $2000-$2800 so you have an idea.
gsistore

 

[Yoyizit]

For more info on why do a heat loss calculation see the following link.
http://www.comfort-calc.net/faq.html
My house was built in 1978 and is about 2800 sq ft of living area. I live in south central PA and my heat loss is about 40k. May heatpump is 3 ton with 10K of electric backup. I have one bank of the electric disconnected. The home still heated OK at 2º OD temps last winter.
Doing my heating degree days my HDD comes out to 1.9 btu's per sq ft. That is a far cry from 6 HDD's per sq ft.

Thanks for the link.
Yes, your house is almost as tight as the Wisconsin Study's low value of 1.7. Probably 95% of the houses (in Wisconsin? In the US? In North America?) are more lossy than yours.

For my house,

838 therms of NG in 90 days = 9.3 therms/day
3100 sq. ft. including basement gives 9.3/3100 = 300 BTU/sq.ft.
2658 HDD/90 = 30 HDD in one day
300/30 = 10 BTU/day/sq.ft./HDD
Effic. factor 0.8
final 8.0

if the average efficiency of my oversized furnace is actually more like 0.4, my house would come in at ~4 BTU/sq. ft./HDD, which was about the average house value in the Wisconsin study.

There is a formula like the one I used in one of the study guides for the PE exam for Mech. Eng.. Some of the chapters deal with HVAC subjects. They used a fudge factor to make their formula come out more closely to measured values, so it's possible all my values read somewhat high.
http://ppi2pass.com/ppi/PPIShop_ct_...8ef4666b5257&gclid=CLj84uX0xJsCFSBN5QodcyvZ_w

ASHRAE probably has an approximate formula like this but their books are not easily available from non-technical libraries.

These type formulas trade accuracy for convenience. Anyone knowing therms used and HDD for their locale can approximate where his/her house falls on the histogram as far as heat loss.

 

[hvaclover]

HHD to determine load is inaccurate.

There are enoguh low cost DIY load calc programs, here is no reason to guess.
Or use rules of thumb.

I was gonna "jump" Einstein for the short form too, but you beat me to it.

 

[janralix]

Thanks for the info, but I'm really ignorant of the technical stuff. I did get out of all your replies that $10K & 4 tons is excessive. However, I can add that I do have excellent (or so I was told) ceiling insulation (@ 8" of rock wool), double-paned Andersen windows (@ half of them new...the other half @ 35 years old), my basement/garage area (not heated or cooled) consistently stays @ 55-70 degrees year-round (garage on the lower end of the range), and my brick house is @ 35 years old.

I was thinking of going all heat pump w/o a gas back-up, but do already have gas heat so I could keep gas heat or use it as back-up to the heat pump.

Also, what is a two-stage unit & what is a variable speed heat pump?

You guys are great...and thanks!

 

[Yoyizit]

xxxxxxxxxx

 

[Yoyizit]

However, I can add that I do have excellent (or so I was told) ceiling insulation (@ 8" of rock wool)

This link
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table
combined with this one
http://en.wikipedia.org/wiki/R-value_(insulation)
says you're a bit low.:confused1: