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inspectorwill

Energy Loss Puzzle

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Have a client and friend with a 2600-2800 sq ft. home with vaulted ceilings near a California snow ski resort. The home sits vacant most of the year. His propane use has been through the roof so I thought I would check it out. Took the infrared camera to looking for cold air infiltration and insulation coverage. Outside temperature was 18-20 degrees F. Turned on the forced air heater at 6 am trying to get a good temperature differential between outside and inside air for the IR scan. Interestingly, no matter how long I ran the heater, I could never get the home interior more than 20-25 degrees above the exterior ambient. The home appeared well insulated and didn't find any outrageous points of energy loss. I found the usual cold air infiltration around some doors, windows and chimney / sidewall intersections. The heater is a 20 year old 100,000 BTU unit with insulated ductwork to all interior rooms. The unit is rated for a 45-75 degree heat rise and actual heat rise from return to register was 40-50 degrees. The home owner keeps the thermostat set at 45 degrees during the winter and I presume on days colder than 20 degrees (which are many), the furnace runs continuously depleting his propane. Could this be a furnace issue or am I missing something with heat loss? It seems to me that after 5 hours of the heater running, I should have obtained a temperature that was more than 20 degrees above outside ambient temperature without some considerable source of heat loss.

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That's a LOT of cold sink to overcome. All those COLD materials are going to take a good long time to heat back up, though I'd think the air temperature might have raised more than that.

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I would get your hands on a blower door, run a test, then leave it running and do another thorough infrared scan. Heat leaving the building is not nearly as easy to find as cold air being sucked in. You can find some truly scary stuff this way. It is certainly true that a blower door creates pressures that may never be duplicated exactly under normal conditions, but it gets you looking in the right places.

I'm assuming, of course, that you've verified that the heating system is actually putting most of those BTUs into the building...

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Am I the only one thinking that furnace is undersized? My house is 1200SF and has a 100K BTU boiler, and if he's actually dealing with 20 degree ambient temps in July, he has far greater heating needs than I.

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What was the actual temp of the hot air coming from the supply vents after running it?

Air temp at the registers was 40-50 degrees higher than return air. Return air when I started the furnace was about 30 degrees. However, I could never get the home more than 20-25 degrees above exterior ambient temp.

I've been contemplating purchasing a blower door. Any recommendations on manufacturer / models, training and certification courses?

I was feeling the furnace was undersized also. However, it seems to me that even with the undersized furnace, the home should have reached a higher interior temperature even with moderate heat loss after 5-6 hours of furnace operation.

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So you are saying the gas (propane) fired furnace after running for several hours was producing 80-90 degree air? Sounds like to me the unit is not only undersized, but not working correctly to begin with. Small or not.

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So you are saying the gas (propane) fired furnace after running for several hours was producing 80-90 degree air? Sounds like to me the unit is not only undersized, but not working correctly to begin with. Small or not.

Yup, the unit is rated for 45-75 degree rise and I was getting 45-50 degree rise.

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His propane use has been through the roof

Sounds like we need some more info here. The unit is 20 years old so presumably at some point in history it was working satisfactorily... otherwise someone would have lost patience and had it serviced or replaced. Did your contact just buy the house? Does he have any info on historical propane usage? Seems to me you should be able to get the house up around 70 on a 20-degree day, but it might take a day or more. Anyway, what else is known about this situation? And, what is the ceiling material on those vaulted ceilings... T&G wood?

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It seems to me that there is not enough information to solve the puzzle. Information you should get / tests you should perform:

blower door testing

duct leakage testing

historical fuel usage and general history of the home and homeowner

Good luck

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I agree that further testing needs to be conducted and am considering going back with the blower door. We don't have history on past propane usage but will attempt to get it through the local provider. The vaulted ceilings are T&G wood. I will have a blower door and training prior to winter and will return for another round of evaluation. Thanks for all the input.

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The T&G ceilings are highly suspect. Run the blower door for 20 or 30 minutes and then take a look at them with your IR.

If you're going to buy a blower door, my rec is to just order a new unit from Energy Conservatory. You can sometimes buy them slightly used on eBay, but the price won't be much less than new, and you won't get a new manometer that way. As far as training goes, I took BPI training but was fortunate to get it through Washington State U, rather than one of the many diploma mills out there. You could also look into the Saturn Online curriculum, and their books. What you need and can benefit from depends a lot on your experience level with construction, building science, and inspecting.

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