Seeing how I have no real knowledge of HVAC systems and furnaces, I come to the great world of Breaktime to pose a question.
My brother has a house, been in it 8 months, and has LP heat. He has never used LP before, but is concerned that he is using too much fuel per month. His monthly fuel usage is 300 gal. Location is central Indiana. His house is a single story with a finished room above the garage, 2500 sq.ft., 9 ft. ceilings, 20×27 great room with cathedral ceiling, 14×17 master bedroom with cathedral ceiling. The system that was installed by the HVAC contractor was a 100,000 BTU, 90% multi-poise gas furnace. All ductwork is routed in the crawl space(except to the room above garage). He is also concerned(annoyed in my opinion) that the furnace cycles too often.
Seeing how I(nor he) have never used LP heat before, is 300 gal. per month reasonable? And how often should the furnace cycle? Any help you can give me would be great, thanks in advance.
Mitch
Replies
no....300 gal is not reasonable.. sounds like he lives in a sieve....
you skipped the most important part ( and it sounds like the builder did too ).... how is it insulated ?
Mike Smith Rhode Island : Design / Build / Repair / Restore
Mitch,
I live in rural northern IL use LP to heat air and water. Over the past 5 years, I have contracted for 1000 gallons in the summer at low prices (this year I paid $0.85/gallon) and usually have some left over by the end of the contract the following June. My house is over 5000 sf and has approximetly 3000 sf of windows/doors. I have to fill the 500 gallon tank once for a normal winter. 300 gallons a month in this climate (and especially this winter which has been very mild until last week) is not reasonable. For a 2500 sf house in this area, I would expect usage on the order of 100 gallons a month.
How often the furnace cycles depends on how it is sized to meet the load, how well the distribution is set up, and where the thermostat is located. When it is -10, my furnace runs maybe 45 minutes out of an hour. When it is 10 it runs maybe 15 minutes in an hour. I run the fan constantly and have a two stage furnace, that fires on low most of the time. When I moved in to this house, the distribution was poor and most of the heat went into one room that had the thermostat. Every 10 minutes it would fire for about 5 - 10 minutes and shut off. It wore out and was replaced, after I installed a decent system of ducts.
How much fuel he is consuming is related only to the tightness and thermal insulation of the home and how warm the space is kept. A programmable thermostat helps and well suited for forced air heat, but there is a problem with this house.
Is the ductwork in the crawlspace insulated and sealed well? Seems unreasonable, but I've seen uninsulated, leaky ducts in newer houses before. Even in an uninsulated crawlspace w/ open foundation vents.
Is the floor under the house insulated?
My last house,1200 sq. ft.. Had all the easily visible ducting insulated in the crawlspace. If you actually went down there, the ducts to the bedrooms were metal w/ taped seams, some of which leaked quite a bit. The floor was insulated, but you needed to close the 4 foundation vents during the winter.
Edited 1/15/2003 4:44:04 PM ET by BILLYG83440
My other brother Mike already said what was on my mind. Insulation package question was so obvious but also do they sleep with half the windows open?.
Excellence is its own reward!
The house is 2x4 construction with unfaced fiberglass in the walls, the windows are sealed well(I made sure of that), and the garage is also fully insulated, blown celllulose in the attic(~8 in.). The crawl block is insulated, but the floors are not. The ductwork is comprised as follows: main trunkline is rigid insulated duct, with the feeders to each register flexible insulated pipe. One thing I realized after reading the replies is that he probably hasn't sealed off his vents in the crawl(there are 19 I think). I'll probably take care of that tomorrow and check out the ductwork under the house. Seeing how I built the house, I want to prevent this from happening on any future homes I build. Thanks for the help.
He has a house with some large spaces and hot air furnace. That hot air will tend to collect at the ceilings. He has two large rooms with cathedral ceilings and other rooms at nine feet high. If you check the temp of the air near the top, I'll bet it is uncomfortably warm. Heating that top foot or so to 85-90° probably costs as much as heating the lower seven feet of volumn. Circulating the air will increase his comfort at less cost. That is one of the benefits of dome homes. They tend to create a natural convective flow of air even though the central ceiling is high and still use less energy to heat.
You also don't mention - unless I missed it - the insulation package for the cathedral ceilings. That is a location thaat often gets neglected while it really needs more attention than most areas of a house.
You name unfaced fibreglass. Why is it not faced? Have you no vapour bar? If that is the case, you could be in for worse problems. Moisture from the house could be migrating to the interior of the walls and wetting the insulation, rendering it ineffective.
What is the humidity in the house? This can also affect user comfort. Too much or too little is uncomfortable. Fourty percent is good for people, less than twenty is better for houses. An uncomfortable person will turn up the thermostat faster than a comfortable person, even though his problem is not always the temperature..
Excellence is its own reward!
ooops.... sorry 'bout dat.... no offense meant....
sure do sound like heap big heat loss someplaceMike Smith Rhode Island : Design / Build / Repair / Restore
I keep re-reading this, looking for clues.
No insulation in floor and possible open crawl vents could be a major source of the problem, especially if any leaks in the ducting.
Is the system installed with a cold air return and is it functioning well?
Also, since this is a new house, is it possible that the furnace was running while construction work was being finished, allowing dusty construction air to be pulled into the plenum and filters? If so, were the filters ever changed? Dirty filters cvan be a cause of the frequent cycling and the reduced airflow could account for some inefficiency..
Excellence is its own reward!
Piffin,
The exterior walls do have a vapor barrier(forgot to mention that), and the cathedral ceilings are all faced fiberglass(r-19). The filter has been changed since construction was completed, but it's something I might do again. I didn't think about the cold-air return(something else to check). I do know that the attic stays cold, I was up there the end of December and was certain that I didn't want to stay in there very long. Thanks for all the pointers/suggestions, I may talk to the HVAC contractor and see what his take is on the situation. Thabks again.
Mitch
when you say the garage is fully insulated ( but not heated , right ? )... let's say the outside temp is 20 F. what is the garage temp ?
and how is the floor over the garage , under that finished room , insulated ? what R-value ?
and the r-19 cathedral ceilings?... no.. not up to code ...
and the uninsulated floor over the crawl... that might be ok if you converted the crawl into an insulated space.. but it's not....
and 9" of cells in the attic... nope...
there are too many weak points in the envelope... when the alberta clipper comes blowin across the indiana winter scape.. it is just not enough...
the house is insulated , but needs more..
good idea, checking out the HVAC system... was the system sized for the insulation spec'd ? Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike,
Right that the R-19 isn't the newest requirement ( What is it now? 30 or 38? I don't do too many new things thathave the option. Most of these old houses don't have the space for more than 19 unless they can afford the bill for sprayed foam) But it has to be more than just that - of course with a high ceiling combined with the low R you are almost pushing heat through. Add to that an uninsulated floor to draw cold in and there's a good explanation. A few leaks in the ducting and some other fine tuning on the furnace...
Does this house have fireplaces?
I've known more than one customer who didn't understand that they can make pretty good airconditioners if they leave the damper open.
I'm still of the opinion that a third of wasted energy in home heating is due to lifestyle stuff. But the fact that this HO is paying attention to the gas bill tells me that he might be conscious.
Here's another thought - is there a gas leak? That could cause a larger gas bill!
.
Excellence is its own reward!
Well, I think I found a problem, thanks in part to BILLYG. I went under the house this afternoon to shut off all the vents(asked my bro if he had done this, his reply: "They shut automatically"). Anyway, I knew there was a problem when I opened the access and felt warm air. After taking care of the vents I looked over the main trunk line and lo and behold, where the ducting was attached to the insulated trunk there was nothing sealing the connections. Another potential problem I found was where the flexible ducting was attached to the connections, some goof used duct tape to seal them. I plan on getting some good tape and go back under there tomorrow to seal all the leaks. I should have known to check these things, but hey, we all have the occasional brain-fart.
Mitch
Hey, glad you found the problem. Trying to heat the great outdoors. Good luck getting it under control.
I've had some pros recommend to use mastic rather then tapes to seal ducts. I've never used it, but I understand it's a joint compound for heating ducts. They said it seals better and holds up better over time. They swore by it. I have only used tapes. With pretty good luck so far.
Enjoy
Bill