another estimate, more confusion

[troyport]

It's hard to tell who to believe and who not to believe. I've had 5 HVAC guys out so far. Actual BTU's for heating are all over the place. I know no one can give me sizing over cyberspace, but I'll ask for thoughts.. 2100 sqft dime a dozen colonial built in 1990. Currently I have a 90k input LP 90% forced air system. Let me ask this question... On a cloudy calm day in NE Ohio where the night temps drop to 25 and the day temps reach 35, how many hours of run time would I expect for a properly sized system? I am asking this way because this is a number that I can actually grasp and even keep notes.. For instance, if the dang furnace is running 12 hours a day, then it isn't going to keep up on a day when it drops to zero. If it runs only 3 hours, maybe it is too big. There's got to be a rule of thumb that a homeowner can use to weed out the bad advice. Thanks in advance, Mike

[JonesHVAC-R]

It's hard to tell who to believe and who not to believe. I've had 5 HVAC guys out so far. Actual BTU's for heating are all over the place. I know no one can give me sizing over cyberspace, but I'll ask for thoughts.. 2100 sqft dime a dozen colonial built in 1990. Currently I have a 90k input LP 90% forced air system. Let me ask this question... On a cloudy calm day in NE Ohio where the night temps drop to 25 and the day temps reach 35, how many hours of run time would I expect for a properly sized system? I am asking this way because this is a number that I can actually grasp and even keep notes.. For instance, if the dang furnace is running 12 hours a day, then it isn't going to keep up on a day when it drops to zero. If it runs only 3 hours, maybe it is too big. There's got to be a rule of thumb that a homeowner can use to weed out the bad advice. Thanks in advance, Mike

Based on location and home you call for around 81,900BTU output (based this on a similar install in Erie, PA). You state you have a 90% 90,000BTU input so it is outputting 81,000BTU. On a colder day, as we know we definately get in this region, you will not be able to keep up.

[BaldLoonie]

Here in Indy, typical 2100 sq ft like that built in 1990 we'd go a 75K-80K input 95%. 60-70K would be cutting a bit close in the rare -10° morning. Prefer 2 staqe or modulating for long run times (with appropriate control).

For $50ish you can download and register the HO version of HVAC-Calc (on the menu bar above) and crunch your own numbers.

[troyport]

I've never had an issue with my current furnace, but I've got 2 guys saying I need a 70K btu input 95%, and one guy saying I need 100K BTU input. Sounds like, in general, the 70 would be too small and the 100 would be too big. I think I'll figure the 2 guys who say I am sized correctly now as best I can, are probably more correct... I'll replace with another 90K. Does this sound reasonable? Mike

[BaldLoonie]

The RIGHT way is do a load calc. If 2 people who have seen the house think 70K, they are probably right. Lots oversize, but dealers don't undersize, they don't want you pissed if you are cold.

[NCHeat]

Get an actual load calc done and find out exactly what you need for our design temps 0 to 5 degrees is a good way to go. 70K to 80K at 95% would be my sight unseen guess. Dont guess, have a load calc done. I also like the 2 stage furnace. They are really paying off this m ild winter so far. Good luck

[troyport]

Currently, I have a 81K output furnace. The bigger new furnace would be a 85K output, the smaller would be a 65K output. If I went with the smaller furnace and it was too small, would I struggle on only the coldest of days, like the 1 day in 5 years... or could I often struggle on cold days? I guess what I am asking is could this be disastrous? FWIW, yesterday was drizzly and cold.. 37 degrees... the t-stat called for heat 3hrs and 38 minutes total for the 24 hour period, if that is any indication of whether my current furnace is appropriate. Thanks, Mike.

[beenthere]

It would only struggle on the coldest days. And often, just adding a little insulation, or doing a little sealing will reduce your heat loss so that a smaller furnace is able to handle the heat loss on those days too.

[skippedover]

Things you cannot control: Codes issues, system sizing requirements, specific features and benefits included on any piece of equipment.

Things you can control; features and benefits you select, overall total cost of the system, environmental issues for outdoor and/or indoor equipment, approximately how much you pay for the system, who does the work for you.

All companies providing you with a proposal should comply with the things you or they cannot control. In our state, a full ACCA Manual 'J' load calculation is required, though many companies do not do one. That's a red flag immediately, as they're already cutting corners to try and get the job, even though they're displaying their lack of ability at the outset. The proposing company should know the features and benefits of all models of the equipment they are proposing to you. The actual size of the equipment should not be a topic of discussion as any company doing a comparable load analysis should come up with the same answer. Whether you select and 80% AFUE or a 90+% AFUE furnace is your choice, provided other influences are not in play (common venting with another condo unit, chimney below standards, etc.). Whether you select multi-staging or modulating or single stage. Whether you include electronic or media air filtering/cleaning, ultra-violet lighting or humidification are all options for you. And finding the right company that you trust to do the work will ultimately be your greatest comfort.

If you've got one or two companies with whom you're impressed but who are offering different size furnaces, then sit them down individually and dig out the answers to the differences. Who actually measured the house room-by-room? Who used one design temperature over a different one. Which one is plausible? Who estimated the insulation factors in your home more accurately? These are all things that can change the sizing result on a furnace. Nobody is saying it's necessarily easy but I'd recommend the work be done now and you can then rest easy for many years.

[troyport]

I found a fill-in-the-blanks chart load calculator on line, where I input details on wall size and r value, ceiling, windows, design temp, etc.. Took a few hours to fill out. funny thing, the initial answer was 68K, then I adjusted the design temp a few degrees either way and got 63K and 85K, then I played with the R value of my attic, jumped the load again back and forth. Makes it sound like if there is a wall someplace in this house that the builder got lazy on and missed a few bats of insulation, I'm screwed... Or if my daughter leaves the bathroom fan on I'm screwed... My Dad says I am WAY overthinking it, and I am starting to agree with him... If I undersize, one day out of every year I can plug in the electric heater and call it a day...

[tipsrfine]

I found a fill-in-the-blanks chart load calculator on line, where I input details on wall size and r value, ceiling, windows, design temp, etc.. Took a few hours to fill out. funny thing, the initial answer was 68K, then I adjusted the design temp a few degrees either way and got 63K and 85K, then I played with the R value of my attic, jumped the load again back and forth. Makes it sound like if there is a wall someplace in this house that the builder got lazy on and missed a few bats of insulation, I'm screwed... Or if my daughter leaves the bathroom fan on I'm screwed... My Dad says I am WAY overthinking it, and I am starting to agree with him... If I undersize, one day out of every year I can plug in the electric heater and call it a day...

I think it's a good thing you played with the numbers and saw how they can affect the results. The best thing to do is to have a full scale energy audit performed on your home by someone certified by either BPI or RESNET. They will do a blower door test to determine how much air leakage your home has. That number can vary significantly from home to home, and anyone doing a manual J calc w/o this test is just guessing at what could account for 30% of the load. They will also use infrared imaging to better determine where those leaks are, and to better determine if you have any hidden insulation issues. Having insulation in your walls that is marked R-15, but is improperly installed and/or is in a wall with air leaks is more like R-5 or worse. Making sure your duct system is sized properly and air sealed (especially if it is in an unconditioned area) is very important also.

[tinner73]

spend the $50 and do the load calc at the top. that will give you an idea of what you need. that will be sized for the coldest day...and it should run most of the day. get a staged furnace for longer run times...a Rheem Mod would be perfect for a guy like you.

[troyport]

When we bought this house, I did a lot to it. it had real lousy single pane basement windows, now they are glass block. I added insulation where the foundation meets the walls, adjusted doors and added seals, better bathroom exhaust fans that closed when not running, replaced seals on the windows and now I put plastic on the windows for the winter. I love that stuff, can't even tell it is there. Added insulation to the attic. Installed seals on all outside-walled switches and outlets, sealed my air ducts in the basement. This was after the first winter, dropped my propane consumption by 20%.

[tipsrfine]

When we bought this house, I did a lot to it. it had real lousy single pane basement windows, now they are glass block. I added insulation where the foundation meets the walls, adjusted doors and added seals, better bathroom exhaust fans that closed when not running, replaced seals on the windows and now I put plastic on the windows for the winter. I love that stuff, can't even tell it is there. Added insulation to the attic. Installed seals on all outside-walled switches and outlets, sealed my air ducts in the basement. This was after the first winter, dropped my propane consumption by 20%.

What kind of insulation did you use "where the foundation meets the walls"? Stuffing fiberglass in there doesn't do the job. The air leakage at that area will just blow through it. If you didn't air seal attic penetrations before insulating it, you should check to make sure you're not getting moisture damage up there, especially if you live in an area with long & cold winters.

[troyport]

All this sizing talk on this thread, had another guy here today, said I'm borderline with the smaller furnace... but probably okay.. But I will be using propane, if the GMVC furnace I thinking about is a 70Kbtu input... should I be concerned since the output of 65K will actually be less because of the propane?

[second opinion]

All this sizing talk on this thread, had another guy here today, said I'm borderline with the smaller furnace... but probably okay.. But I will be using propane, if the GMVC furnace I thinking about is a 70Kbtu input... should I be concerned since the output of 65K will actually be less because of the propane?

How does propane affect your output?

[JonesHVAC-R]

How does propane affect your output?

I have that same question as I saw someone else say they had it in some downloaded specs from a manufacturer... it is known to us in the HVAC field that propane delivers more btu/hr than NG. Example: at 60 °F a flow of 1 cubic foot/hr of natural gas will deliver 1030 btu/hr but 1 cubic foot/hr of propane will deliver 2488 btu/hr...about 2.5 times more heat!:.02:

[beenthere]

How does propane affect your output?

Often manufacturers derate their furnaces when converted to propane because it requires more combustion air per BTU for a clean burn.

[Kevin Weaver]

Get an actual load calc done and find out exactly what you need for our design temps 0 to 5 degrees is a good way to go. 70K to 80K at 95% would be my sight unseen guess. Dont guess, have a load calc done. I also like the 2 stage furnace. They are really paying off this m ild winter so far. Good luck

if you e-mail me your address, i have a cyber space program that will do the calculations for me/you. Any additional information like attic insulation, 2 story or ranch... as much info as you can.

[George2]

I found a fill-in-the-blanks chart load calculator on line, where I input details on wall size and r value, ceiling, windows, design temp, etc.. Took a few hours to fill out. funny thing, the initial answer was 68K, then I adjusted the design temp a few degrees either way and got 63K and 85K, then I played with the R value of my attic, jumped the load again back and forth. Makes it sound like if there is a wall someplace in this house that the builder got lazy on and missed a few bats of insulation, I'm screwed... Or if my daughter leaves the bathroom fan on I'm screwed... My Dad says I am WAY overthinking it, and I am starting to agree with him... If I undersize, one day out of every year I can plug in the electric heater and call it a day...

Good for you "for over thinking" ur HVAC purchace. If more people were like you, our business would have a better name.

Not so many disappointed customers! I used to get calls all the time to "fix" other contractor problems.

When we did homeshows, people would come to our booth and tell us, "Geothermal doesn't work, it won't keep my house warm."

[beenthere]

Homeowner314, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

You can find the rules for posting and qualifications here (http://hvac-talk.com/vbb/showthread.php?t=957002).




Further infractions may result in loss of posting privileges.

[jpsmith1cm]

CAVALIER MECHANICAL GROUP

this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

You can find the rules for posting and qualifications here (http://hvac-talk.com/vbb/showthread.php?t=957002).




Further infractions may result in loss of posting privileges.

You post in this thread and the other have been deleted.

[JonesHVAC-R]

Often manufacturers derate their furnaces when converted to propane because it requires more combustion air per BTU for a clean burn.

I buy that. I guess I haven't really paid much attention to them derating for LP. Kind of odd though considering you change out not only the orifices but also the regulator spring... The spring obviously having the biggest factor.

[beenthere]

Propane has a much high SG then nat gas. So more pressure is needed to move it through the smaller orifices.

Carrier has some furnaces out that only run 3.5" on propane.

[catmanacman]

Once you decide on a contractor and a size i would also look at adding a heat pump and going dual fuel ,depending on your electric rate there can be a big savings on utility's , here in virgina a dual fuel system can lower propane usage by 40 to 60 percent and at 3.25 a gal it can add up

[George2]

Once you decide on a contractor and a size i would also look at adding a heat pump and going dual fuel ,depending on your electric rate there can be a big savings on utility's , here in virgina a dual fuel system can lower propane usage by 40 to 60 percent and at 3.25 a gal it can add up

Cat beat me to it. Also here in the midwest, propane is expensive to operate verse a duel fuel or also known as a "hybrid" system. The payback is very fast.

Carrier/Bryant have a variable-speed HP that is amazing (and expensive).

Those dealers can give you a operational cost comparision in minutes on 4 differant system combinations.

[troyport]

So if propane actually produces more heat, if I am borderline with a 70K unit, but it gets converted to propane, am I actually getting more out of it? And if it needs more combustion air to operate, if I am lucky enough that the venting of the unit is nowhere near the maximum footage/elbows allowed, then is it safe to assume that I have ample air to feed the propane?
Kevin: I emailed you a few days ago... but I haven't heard back.. should I email you again? thanks. Mike.

[beenthere]

You don't get more heat from it.