my gas bill as a gauge of system efficiency

bradslees

Not sure whether to put this here or in the gas forum, but here goes.



I'm new to homeownership and have been learning a lot and tinkering a little based on "The Lost Art..." and this site. My goal is to get a quiet, stable system that is running efficiently. Quiet and stable are pretty easy to observe (and I'm still working on it) but I'm realizing that efficiency is a bit harder to quantify. Towards that end, I was hoping maybe some of you could chime in on what a reasonable amount of gas would be to heat my ~2200 sq. ft home just outside of Boston. Gas-fired boiler in the finished basement, two levels above.



This month I used 203 therms (197 CCF?). In August I used 14 therms (though I wasn't living in the house full time yet at that point).

jumper

depends on house

Modern windows? Weatherstripping? Insulation?

SWEI

The best metric to compare

Is BTUs per degree-day per square foot.  http://www.degreedays.net/ will let you download data from a personal weather station near you.  Get the daily data for several winter months, then break it up into monthly chunks to match your gas meter readings.  Add those up and do the math.



That number is indicative of the overall efficiency of your system (including the building envelope, the heating appliance, and the distribution and control systems.)

Gordy

HDD. Per square foot

Like SWEI said.



Couple different ways to do it. But you need accurate information to plug in.



You need to know how many other appliances use gas I assume there is others from your august bill. DWH, stove, cook top, dryer, BBQ grill etc.



A way to determine how long the boiler runs in a 24 hour period, my particular thermostat can show how long there was a call for heating in a 24 hour period, and a season total that can be reset.



A good web site that can give you daily HDD for your location. I use weather underground .com



An accurate square footage of the space being heated by the boiler.



The DOE boiler OUTPUT of your boiler. This will give you an accurate measure of how many btus the house needs to maintain its setpoint.



The formula is as follows



Boiler run time in 24 hours * boiler btu output / HDD for 24 hour period / square feet of heated space= HDD per SF



This will not correlate to therms on the gas bill because those numbers will be based on boiler input, and other gas appliances.



Average insulated home is around 10-15 btus a sf per HDD.

bradslees

thanks

for all the good info.

i will check it out.

Chris_L

Here is some comparative data...

This is interesting stuff.  This article gives some indication of the range of residential Btu/HDD-SF values: http://www.homeenergy.org/show/article/nav/consumerinformation/page/2/id/825 even if it is a few years old.



The numbers are based on total gas consumption rather than heat output by the boiler, which seems to make more sense to me.  That way you are accounting for the boiler efficiency.  As for including gas usage for other appliances, just look at a gas bill for a month when your heat is off.  You could subtract that from the total, or if you are like me, you'll see that in winter almost all the gas is consumed by the boiler (single pipe, atmospheric steam boiler).



Here are a couple comparative figures for my Boston area 1920's home (actually the first floor unit of a 2-family home): 14.6 Btu/HDD-SF in 2008 with no insulation in the walls; 10.9 Btu/HDD-SF in 2009 after cellulose insulation was blown in (both numbers based on total gas consumption).

Bob Gagnon plumbing and heating

Is It Steam?

Maybe about $400 for the colder months.



Thanks, Bob Gagnon

Gordy

Variables

If you track daily pay attention to weather conditions by that I mean s follows.



Solar gain the lack of, or presence of.



Big one Is wind also. Direction etc.



Ventilation. Bath fans, oven, dryer, fireplaces especially masonry.



You will find that BTU per HDD sf is a pretty constant number no matter the temp unless there is excessive wind, ventilation, and lack,of solar gain.



Interesting to see how it pans out to a heat loss calculation program if you are doing a future boiler replacement, or to see if your present boiler is grossly oversized.