Current Furnace BTU rating method changed from earlier method!!!!!

[mm]

I wish I could tell everyone with an oil, or gas?, furnace, but this is a start.

It seems that the current furnace BTU rating method has changed from earlier method, the one used when my furnace was new, 31 years ago!!!!!** Maybe that accounts for many of the people who have installed the wrong size furnace in their house.

**They don't actually *rate* mine as 85,000, but the brochure and the owner's manual refer to Model 58V and specifically 58HV085.

The 4th character V was based on the physical arrangement and could be V, E, H, L or C, for highboy, lowboy, horizontal, upflow, and downflow.

The 5th to 7th characters, 085, 100, 125 are the bonnet capacity, the output K-BTUs. For the horizontal model, this was true for these numbers and also for 150, 200, 250, and 335. The number-suffix of the model and the output are always the same.

So that's why I say my furnace was rated on its output. Is that fair?

Someone here pointed out that if it says 85,000 BTU, that refers to the amount of fuel used, the heat input of the furnace.

And that if the furnace is 90% or 80% efficient, the output is only 90 or 80% of the input.

Since I have now an 85,000 BTU furnace and it's definitely sufficient, and since the blueprints themselves say 85,000 on them, I was looking for an 85,000 btu furnace, but since now that woould be the input, I'd end up with one that was too small. Alas and alack, that would be bad.

Now I'm ignorant, and maybe stupid, and not in the business, but I'll bet even some young pros could make the same mistake. "You have

150,000 now, we'll put in the same thing."

Later another installer says that there should have been a load calculation, because that is his first step, and the homeowner thinks that's the core of the problem, but I wonder how many were first befuddled by this change in rating method.

When did the current method begin?

BTW, I'm glad I learned all this before I saw this ad on ebay today: "This is a used Thermopride upflow 85,000 BTU oil fired furnace. It was installed in November of 2009 and used only four months. The house was 75% heated with a wood burning stove and the furnace was only on during sleeping hours. This unit is excellent condition. We changed over to gas. The return is on the bottom of the unit and as was told that it also can be from the side. The dimensions 24x33x56, model # oh5-85. Webside for the unit is

"

The requested starting bid is $500. The furnace is shiny clean inside. picture 1:

's in driving distance for me, but it's too small for me, but there are occasionally others with such good stories. Do you believe their story?

[trader4]

I don't know about your specific furnace and it may be different for oil than gas. But I'm sitting here looking at the documentation for my previous NG furnace, a 27 year old Ruud. The first page has the secret decoder for the model number and the middle 3 digits are the INPUT BTUs, eg 075=3D 75K input BTUs.

That is exactly how the new gas furnaces are labeled and marketed.

Correct, at least for gas

When I was getting estimates, every installer knew about input vs output BTUs. None of them recommended replacing the old 150K with another

150K. Not sure if that's even possible, as the largest I've seen today is 120K. Three recommended that, two recommended 100K, both 95% efficient. I believe either of those would have been OK.

Yes, that's supposed to be the correct starting point according to most of what I've heard too. None of the 5 companies I had did one though. Only two of them measured the sq ft of the house. I can understand why they didn't. The manual J takes a significant amount of time and since they are only giving an estimate, they would be wasting a lot of their time.

Here's my thinking. You already have an excellent reference point. That is the performance of your current furnace, ie measuring how long it runs during cold periods. Knowing that and it's efficieny, IMO, is probably more accurate than doing the manual J, which is a lot of work.

Now we get to another issue, which is how long the furnace should run if it's correctly sized. You will find most "experts" saying it should run close to all the time on the coldest days. That in turn brings up more issues:

What defines "coldest days"?

Lets say we take it to mean the coldest day in the last 20 years. If we size the furnace to run all the time on such a day, what will it do on days when it's 10 or 15 deg warmer than that? There will be a lot more of those days in the years ahead than that single coldest day. It will be running less. But, what about it's ability to recover from a lower set temp? If you set it back at night, as most people do, what happens? Or if you come home at a different time some days and set the heat back up. How long will it take to recover? IMO, if you size it to run 100% on the coldest day, then you're still going to have a very long recovery time on many other days when the temps are 10 or 15 warmer. I don't know about you, but if I come home unexpectedly, I don't want to wait 5 hours for the temp to recover. For example, I go away on trips and set it back to 50. My system recovers at about 5.25 deg an hour. And with that recovery rate, it's only running about 35% of the time during some of the very coldest days. Hence, while a smaller furnace would keep it warm during the coldest days, for recovery issues, I would not want a smaller furnace. If you get a furnace that runs 100% on the coldest day, then you're going to have many days where you effectively can't even set it back overnight to save fuel.

You don't want it so large that it short cycles and only runs for a brief period on moderate days either. It should have enough run time to evenly circulate the air around at least a reasonable amount.

I would investigate further as to how the ratings are done with an oil furnace. My guess is that they haven't changed and this furnace has exactly the same input BTU rating as your current furnace.

As to buying stuff on Ebay, the usual rules apply. Have they sold a lot of similar stuff and have excellent feedback? What was the negative feedback for? Is it nearby so you can go pick it up, inspect before paying? You have to be careful and know what you're doing. But if you do, there are excellent deals on Ebay and I would consider buying a furnace there.

[jamesgangnc]

I did buy a new furnace off ebay from a company that was selling unclaimed freight. I also see there are some ebay sellers that routinely sell new hvac equipment. Mostly goodman(janitrol). I have some of the goodman stuff that I got locally and it's ok these days. You're usually better off if you can find someone locally that has a license and can buy the equipment from a local supplier like johnstons. I have not seen any bargains on ebay for new stuff and you usually have to add $100 or more to ship it freight.

Having two houses and a condo totalling 6 hvac systems I'm in the mode of diy when ever possible. I can tell everyone that at least with r22 systems there is nothing wrong with using solver solder instead of brazing the copper lines. You can get small silver solder kits with flux for around $10. If you solder you don't really have to have a nitrogen setup because you won't create a lot of oxidation. It's just like soldering copper water pipe. A vaccuum pump is still a good idea though. Especially with used equipment as you have no idea it's history. Vacuum all day and install a filter/dryer as well.

I have bought used stuff off craigs list because that gives you the oppportunity to look at it first. I'd only consider used equipment that is a few years old. Installation is a big piece of work and it's silly to install a piece of hvac equipment that is already half way through it's life expectancy.

[DT]

The data from your old furnace company is not necessarily universal. I have the receipt from the Chysler Air-Temp that was installed in my house in 1973, before I purchased the house. It is for a 100,000 btu furnace.

I removed that furnace many years ago, but the rating plate read,

100,000 input, 60,000 btu maximum bonnet capacity.

I replaced it with an 80%, 75,000 btu furnace (same 60,000 btu output) and it easily matches the old unit.

So that is a 1970s furnace with the standard rating system.

[mm]

It's either that gas IS different from oil or that some change occurred beween 32** years ago and 27 years ago. Somehow I think you're right, but I don't know why I think that.

** Mine is really closer to 32 now.

Of course since gas furnaces are so much more efficient now, your input BTU requirement would go down, even as your output btu requirement remained the same. If you went from 70 to 95 efficient that's more than 33% more efficient, so you could go down 33% in input. If you had 80 and went to 95, that is an amost 20% increase in efficiency, so I'm not sure it would make up for a 33% decrease in input.

None of the 4 guys who came out here measured the load either. (The first guy never got back to me with a price, afaik?)

I don't think mine ever does that. What is their reason to go so small, to save money on the furnace, or something better, like the reason one shouldn't have too big an AC unit, because it makes one feel clammy?

Good point.

I'm not sure how long mine takes, but it's never seemed like too much. (I tend to leave my coat on when I come in from the cold, even when it's warm inside.)

I don't think I've ever waited more than an hour, probalby not more than 30 minutes, but then again, I have 85,000 BTUS for a 1400 ft2 house (plus basement). I don't know how much they would recommend for me now, but the architect said 85K.

I think you're right.

1:> It's in driving distance for me, but it's too small for me, but there

Well, until your reply, I thought it was too small for me, but maybe it's not. I was mostly dubious about this kind of story. Of course it must happen once in a while, but once one has read it somewhere, he might want to use it whenever he has a clean-looking furnace. Or maybe dirty ones can be cleaned.

This is the first item. And while the ad never quite says he's homeowner, it comes close, yet his ebay id is abcabchomeimprovements. I wonder if he put in the new one and took out the old one, which would be okay, except it wouldn't be possible to talk to the guy who actually knows how old it is. Maybe it was used more than 4 months.

I don't want to take mine out until spring, and I really don't have the space to store a second one at my house until then. I have a storage locker that would hold it, but that doubles the loading and unloading work involved. So in a way I shouldn't even read the auctions before spring, but I want to know what is out there.

[mm]

So do you forego the warranty? Even if there was a 5 year warranty and it's only a couple years old?

I thought by having a licensed installer do the final parts of the installation, , measure with the proper gauges, adjust all the adjustments, and also verify everything I had done, I'd be okay on the guarantee. But one company says that no furnace of theirs bought over the internet and sold directly to the consumer is warranted.

So I've already lined up an installer and I thought, well he could buy it for me, but that has its own problems and further down on the warranty page, it seemed to say that just being sold on the internet means no warranty (no matter who bought it, I guess.)

I had never even heard of Comfort-Aire and could find little about it on the web, but then I saw that half of the models the local large heating and airconditioning supply house sells are Comfort-Aire. The other half are Dayton. Surely they couldnt' be selling crap, but I don't konw if Dayton is grade A and Comfort-Aire is their C+ model.

Another problem for me that won't be easy is

[mm]

I'm glad you remember.

Well this is very enlightening (and confusing at the same time). I should have mentioned that mine is a Carrier, who I didnt' think was some beatnik hippie namby-pamby non-conformist outfit.

I guess the next logical step is to go look at Carrier now and see how they label their furnaces. Or maybe to email Carrier or ask on alt.hvac.

[trader4]

I'd say in most cases, you wouldn't get warranty coverage on used HVAC, at least not through the manufacturer. At least some of them require that for the full warranty the unit must be registered within a few months of it being installed. I'd bet they further restrict the warranty to the original owner only, etc.

I've seen that too. It probably varies from company to company. Some of the HVAC stores selling eqpt online say they will handle and process warrranties for parts. So, assuming they do, you would have warranty coverage through them for parts. But..... that assumes you can wait for the time it takes to probably send them the part, have them send a new one, etc. Not the same as having the local HVAC guy come over and fix it in a day or two. And I think if you buy it online, you're always going to be out the labor, if any. But, given that you can buy a whole new furnace for $1800, if you save $3000 over a local guy the warranty issues may not seem that big anymore.

Probably another grey area.

[trader4]

LOL. I had one guy calling me every day to follow up. He was almost

2x higher than the lowest guy. The lowest guy was there to answer any questions, but never followed up beyond that. And then there was the guy recommended by a good friend. A neighbor of his. Took him a week to come buy and look. Then said he'd work up a quote and never heard from him again. I think the best ones were the guys that sat down at my kitchen table and wrote out the quote on the spot. Geez, it aint' rocket science. One would think they could have a binder with pricing info and all just do it on the spot. It's basically just a few line items.

If it's oversized in a major way, I think the issue is it won't have enough run time to even out the heat in the house. It could kick the thermostat off and you'd have wider variation, room to room. Also, possibly notice hot spots when it's running compared to correctly sized one. Still, the furnaces themselves are generally the same efficiency, within the same product line. So, if you have one that is 20% oversized, I don't see any efficiency issues, or increased cost to run it. You get less heat out, it runs longer and winds up burning the same amount of gas. If anything, oversizing might mean it costs less, because you could have less blower run time, assuming the blower sizes are the same.

It depends on how far it's set back. Mine comes up at about 5.25deg an hour when it's in the teens outside.

[mm]

Yes, that's the case with alpinehomeair.com . They say they warranty the stuff themselves.

I thought you would say I send the part to them, they send it to the manufacture, and back again in two legs. If it's only one back and forth, that's not so bad.

So far their service has been great. Ordered the little humidifier I needed Saturday night. It came Tuesday at noon. Answered the phone quickly, and were competent on the phone. And they sell, and describe online (very good webpage), all the extra parts needed for installation, plenum kit, filter holder, corners to set the furnace on, high-temp evaporator tray (needed for oil furnaces that burn hotter than gas) etc. (Everything but the elusive flexible duct connector, which someone here showed me where to get. )

I don't know if I would save 3000, maybe 2000, but yes, exactly.

BTW, I had the chimney cleaned Monday, 170 dollars. And that whiff of oil smell at the start of most cycles, I haven't had since then.

I've thought before that it was gone, but never for 3 whole days.

He was slow and thorough and took almost 3 hours, including up on the roof. He didn't say it was "too dirty to clean" like the previous guy, 170

[mm]

Yeah. They have the same set of numbers to add up for everyone and for most they probably push 2 or 3 oil furnace and 2 or 3 gas furnaces.

Okay, good reasons not to get too big.

Okay.

I've never checked on that. It sounds like a good number to know, so maybe I will.

[mm]

Maybe I shoudln't have but I called Carrier, and the very nice girl on the other end was so sweet and helpful and I thought I explained the question well, and after a minute or two she came back and was going to send me the manual for the furnace I have now.

I asked her if that was still the system they used for picking model numbers and she said yes, off the top of her head, without further research, and I don't trust her anymore. I sort of knew the question was too hard for someone who doesn't actually deal with real models and real outputs.

Rather than my 3 ideas above, I'll have to hunt for some Carrier oil furnaces online and compare model numbers, ratings, input and output. I should have thought f

[Mark]

I agree 100%

.. if you know the BTU OUTPUT of your current furnace and you know how long the on/off cycles are and how well your home is heated under various conditions, you will get a much more accurate result compared to starting from a scratch estimation based on square footage etc..

Mark

[The Daring Dufas]

Comfort-Aire is another generic HVAC unit that may come off the same assembly line as other contractor/builder grade equipment. I've installed and repaired a lot of HVAC equipment and the builder grade units all look very much alike on the inside.

TDD

[mm]

So contractor grade means it won't last 32 years like the Carrier, only about 20??

And it will break 1 or 2 more times or more seriously than a grade A brand during that time??

Or what is likely? :)

[mm]

I had to hunt quite a bit. A lot of the pdf documents said nothing about btus, but I finally found one.

They have changed afaict. Carrier now rates oil furnaces on "Input (BTUH)".

And they call the output Heating Capacity.

The first 5 characters of the full model number are the model. The next 3 numbers are input capacity, and with a multi-nozzle, multi-usage model (many, most or all of them are like that now, not just carrier) the 3 numbers are the highest input used.

So the Carrier girl was sweet, but I think she was wrong.

[mm]

1:> It's in driving distance for me, but it's too small for me, but there

Okay, that might be it.

I had a couple questions and I called the ebay seller and he said he was looking at the manual and the 85,000 was output, but I can find out by checking out the model online. It's too cold and snowy to go buy a furnace today anyhow. And I've been up since 4:30.

Thanks.

[hallerb]

The time to install a furnce is mid spring.NOT MIDDLE OF WINTER:(

They make multi input furnaces which increase efficency.

They run at say 65% of rated output, and if its not too cold thats fine and the furnace turns off.

But if its super cold the furnace continues to run and the unit inceases it btu output.

this for zero weather. Its a more expensive and complicated furnace but gains a few % efficency.

You have to remember most furnace installers put in LOTS of furnaces. If your home is a tract home they go with what worked the last 100 furnace installs:)

Why waste time doing a heat loss calculation if you already know the answer?

[The Daring Dufas]

If you own a cheap car and service it regularly, it will last longer than an expensive car that receives no service. One thing I see with cheap HVAC systems is more corrosion than pricey systems. I worked on a Carrier unit for an old fellow who had purchased it back in the 70's and it was the most expensive unit Carrier produced at the time. It had stainless steel screws and there was no rust on the metal covers and brackets. A more expensive system may have more safety controls than a cheap builder grade system. Safeties that are often missing from the cheaper units are anti short cycle timers, high and low pressure cut out switches and condenser fan cycling controls. I ordered a three phase unit with all the extras including a 3 phase power and voltage monitor and have never had to do anything to it except clean it and change the optional 2 inch thick pleated air filters. One of the things I will install on any HVAC system in a rural area are hard wired surge arresters. This is something I'd like to see as a standard feature because it prevents a lot of damage to circuit boards, fans and compressors.

TDD

[clare]

What you WANT is a 2 stage furnace. It runs on low most of the time, but if it gets cold enough that the furnace runs more than, IIRC, 20 minutes, it kicks onto high. I just dug out the manual and checked the operation - with single stage thermostat (which is what I have)

1)Thermostat calls for heat 2)Inducer motor starts on high High fire solenoid energizes 3)After 3 seconds of pre-purge the pilot valve opens and the ignitor starts to warm up 4)After the pilot lights, the main burners energize on high and light 5)Timed from the opening of the gas valve,the control will delay the Heat Fan On Delay Time before switching the inducer to low speed, de-energizing the high fire solenoid and the fan switches to low speed. 6) Timed from the initial thermostat call for heat, if the call for heat still exists after the low fire delay time(12 minutes) expires, the inducer switches to high speed, the high fire solenoid energizes, and the fan switches to high heat speed.

My furnace is a NTP6050fb, rated at input of 50,000 and 35,000 btu, and output of 40,000 and 28000 btu. It is the smallest "residential" furnace I could buy here in Ontario and the dealer said it is still oversized for my Aprox 20X30 foot 2 story home with finished basement in central Ontario. Last week when we had -26 degree temperatures the furnace ran about 8 hours a day - so I think I'd believe him that the furnace is oversized. Last year's total gas bill was about $700.

A few times in our recent cold-snap I noticed the inducer fan kicking on to high, which virtually never happens during our "normal" winter weather.

We had 2 windows replaced during that cold snap - so had the furnace shut off for about 4 hours (no use heating the great outdoors) and after turning the furnace back on, we were back up to temperature in well under an hour.

We set back the temperature every night - and it is a very rare occurrence to have the furnace run more than 20 minutes in the morning to bring it back up to temperature.

1:> It's in driving distance for me, but it's too small for me, but there