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# calculation heat loss with consumption and HDD...

## calculation heat loss with consumption and HDD...

#1
01-12-11, 09:58 PM
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Join Date: Sep 2009
Location: Grand Rapids, MI
Posts: 86
calculation heat loss with consumption and HDD...

I have a 960sq/ft foundation bilevel built in 2001, exterior dimensions are 24x40, lower level is 960sqft with 8ft ceiling, 4ft underground. Upper level is 960sqft with 8ft ceiling on almost half and 12ft cathedral ceiling on other half.

Attic is R60, side walls basement and upper level appear to be R20, double pane windows around 250sq/ft... not sure on efficiency.

Using 75,000btu input / 60,000 output 80% single stage furnace heating all of both levels with a HDD of 44 (69 inside/25 outside) I consistantly heat at 15625 btu (12,500 actual heat BTU @ 80% efficiency)

How does my home fair for efficiency and heat loss? Reason I ask is i'm considering upgrading to a 4000sq/ft ranch with 2000sq/ft main level and a finished basement... built either new or just a couple years old... can I expect anywhere near similar heat loss/cost offset by the new house having a 95+% furnace and what things could I ask/look for in the new house to make it more efficient than this one?

Also shouldn't this current house have more like a 40,000 output furance?

#2
01-13-11, 05:23 AM
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Join Date: Oct 2008
Location: New England
Posts: 9,460
Your description sounds reasonable, but difficult to put a number on your performance. There are many DIY calculators out there to let you play. builditsolar.com has one.

A couple of the details missing would be your air leakage number, and the insulation in that cathedral ceiling, plus rim joist and band joist treatment, and there are others.

The more accurate number would be your actual fuel use. When I calculate someone's heat loss I like to compare it to the real world to make sure my numbers are correct. Absent any real numbers, then you are stuck with the calculated loss.

As for the anticipated performance of a new home, unless you request an energy audit or rating, the previous home owner and/or builder will tell you everything is perfect, doubtful. The basic principle is bigger will use more energy. That can be overcome, but generally requires you watching every step of construction or having it fully tested once done.

One of the indicators of a well insulated home is a tight home and if tight, it should/might have an air exchanger (HRV or ERV) installed with the appropriate numbers to tell you it was sized correctly. No numbers, and it might be decoration to make you think everything was done correctly.

Basically, a house that is really built to be energy efficient will proudly display all of the testing and details that went into its construction.

Bottom line, what you have is good. Your thinking is good. And what you buy next can be better.

Bud

#3
01-13-11, 07:24 AM
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Join Date: Oct 2004
Location: PA
Posts: 2,227
i'd pay 400 for an energy auditor to come in and do a blower and infrared test if you are serious about the house and worried about efficiency. That way you have independent figures to work with, and perhaps even negotiate with. One other thing i'd ask for is to see their heating bills for the past 2 years. They would probably look at you weird but hey, you are paying \$\$\$ for the house so why not. I've seen some MLS listings with it in so it's not really an unreasonable request. in this market i'd say they should go above and beyond to give you what you want.

#4
01-13-11, 07:34 AM
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Join Date: Sep 2009
Location: Grand Rapids, MI
Posts: 86
I'll most likely be purchasing new and most builders now tout this 2x6 framing and "r30 effective" sidewall insulation... but if it's not much / similar to the efficiency of my current home it's all for not and the bill's going to be more expensive.

Bud: there's R60 in the whole attic/ceiling

#5
01-13-11, 09:51 AM
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Join Date: Oct 2008
Location: New England
Posts: 9,460
It's terms like "effective" that concern me and the R-60 would require about 18" of insulation. Special trusses and you can get that over most of the area, but most builders don't go to that expense. I'm not saying you don't have it, but if the determination comes from an independent energy audit, then you can have more confidence.

When you mention a finished basement for the extra space, remember, most basements should never be finished (IMO) as they must be built to be dry from the start. Lots of "Building Science" info on the problems with basements.

To double your square footage and keep your energy costs the same, you would have to cut your energy loss per sq. ft. in half, on average. If you specified how the house should be build, that would be easy, at a price. But few existing homes that were built that way are for sale.

Bud

#6
01-13-11, 11:51 AM
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Join Date: Oct 2004
Location: PA
Posts: 2,227
even custom designed, i'd have to think that kind of house would require a long term commitment to staying there to break even with the extra installed savings devices

which is why, even though there are many factors to consider, seeing their electric and heating bills for the past few years is the only true way of even getting a base number to compare. maybe they kept their house at 60 in winter and 80 in summer and that will not be a very valid comparison, but some data is better than none since costs are of concern to you.

this thread reminds me of something i heard ones about electric heat, they said 100% of all the electricity is going to heat your room and there is no waste going up any chimney. I believe that is a true statement but that doesnt mean it's cheap!

#7
01-13-11, 12:44 PM
Member
Join Date: Sep 2009
Location: Grand Rapids, MI
Posts: 86
Bud: It was 9" when I moved in, I had it increased to 18"... the house is a bilevel/raisedranch so the basement floor is "legal"... there are no humidity or moisture problems in the basement. It maintains temperature very close to the main level and is 100% useable.

The main question here is with a new structure I know i'm going to get 2x6 walls and better sidewall insulation, a more efficient furnace and whatever else has "changed" since when mine was built in 2001... i'm trying to determine what could be done to make the efficiency similar if not just a little more expensive... also i'm trying to benchmark how efficient my current place is.

As it stands right now with an indoor temperature of 69 and an outdoor temperature of 25 and no solar gain it requires 15360btu per hour to maintain 69f. This goes down with sunshine and the furnace is 80% so we'd be in the 12,000 range with a 95%'er