Gas and Oil Home Heating Furnaces - When to replace a working gas furnace?

Hi,

I have a gas furnace that's rapidly approaching 50 years of service and I'm curious whether or not I should be seriously considering replacing it before it breaks for imminent safety dangers or economic reasons.

In the 15 years that I've been in the house, the gas valve and fan/limit control failed and have been replaced.

I have the gas company come out each year to check for possible problems but none have ever been found with regards to CO or gas leaks. The inspector this year said she saw "stress marks" in the metal of the heat exchanger but no evidence of holes or cracks yet.

While it's been a few years since I last had a HVAC technician out to work on the unit, I have a tech scheduled to come out in a week to clean out the unit and check the heat exchanger more carefully just in case.

Now for responses to the standard questions:

1. In which area you live and ambient temperatures you usually experience.
Southern California; daytime highs in the summer exceed 100 F; lows in the winter are typically in the 40s with very occasional days dipping into the low to mid 30s.

2. House style and construction details.
1961 tri-level home w/ 2850 sq. ft. and a southern exposure. Exterior is stucco and interior walls are plaster with fiberglass insulation of R-10 or less along exterior walls. Attic has a few inches of blown in fiberglass, however, the living room has an 18 ft. vaulted ceiling with no insulation above. Crawl space is uninsulated. Windows are single-pane with aluminum frames. House also has three single-pane sliding glass doors on the north side with aluminum frames. Roof is shake shingles.

3. Make, model and age of equipment related to the problem.
Furnace is the original 1961 beast.
Make: Holly Forced Air
Model: 140 VF
Serial: 332
Input: 140,000 BTU/hr
Bonnet Capacity: 112,000 BTU/hr
http://i829.photobucket.com/albums/zz220/Jason986/P1020565-1.jpg

The house does not have air conditioning.

4. Fuel type.
Natural Gas

5. Thermostat type.
Hunter Model 44550 Programmable

6. Anything else that would be useful. No detail is too small.
The heating system has nine vents and three returns. The majority of the ductwork is in unconditioned spaces (attic, crawlspace). Total runtime of the furnace over the last 12 months was ~320 hours according to the thermostat.

Below is the wiring diagram for the entire furnace:
http://i829.photobucket.com/albums/zz220/Jason986/P1020568.jpg

Each floor of the house has hardwired CO and smoke detectors. The room with the furnace and water heater also has a hardwired heat detector. All alarms are tied into a home alarm system w/ central station monitoring.

Long winded post aside, should I start getting estimates to replace this furnace? In your professional opinions, why or why not? And regardless of whether or not this thing should be replaced, is there anything in particular I should ask the technician I have coming out to do / look at / test while he's here?

Thanks in advance for your advice and sorry for the long post.

First of all it has lived WAY past it's normal life expectancy & with it showing "stress marks" I would be pre-emptive & get it before it gets me.

Secondly, it is probably grossly oversized for the house. Presuming the furnace has a standing pilot, it's annual fuel efficiency is likely around 60% where modern equipment is at least 80%. Unless your gas is dirt cheap, a smaller & more efficient furnace should pay for itself in just a few years in gas savings.

Sounds to me that they sized it based on how inefficient that large house is (based on your list of things about the house). My first thought was they needed something big, with a big blower in it, to move the a/c. I thought it was always swimming trunks weather in southern Cal. ?????

rapidly approaching 50 years of service and I'm curious whether or not I should be seriously considering replacing it before it breaks for imminent safety dangers or economic reasons.

Its without a doubt time to replace it. As "Grady" stated its more then likely oversized. Make sure the contractors giving quotes to a manual J to properly size new equipment.

On another note, a heat pump may be a good alternative for you, less expensive to run and you will have cooling. Nows the time with all the tax credits out there.

There is no reason to replace this boiler as its working OK.
However, there is every reason to improve the insulation of your home.
With better insulation there will be many morning and evenings when the heating will not be required.
Start by checking for air leaks through holes in the ceilings walls and floors.
Most heat is lost through holes, with the heat sucked out by the passing wind.
Buy an infrared temperature gauge and scan the ceilings walls and floors on a cold night looking for places where there is little or no insulation, this will be indicated by by a lower figure.
Consider fitting sheets of polystyrene (cut to size) between the rafters and joists.
You will be amazed how much cooler the home will be in summer.
And how much money you will save on heating during the winter.

There is no reason to replace this boiler as its working OK.


Its 50yr old, while what you say about insulation is true. Replacing that thing with a properly sized 95% eff variable speed furnace would cut the gas bill dramatically.

A crack in the heat exchanger = Carbon monoxide = death, no amount of insulation will cure that.

A crack in the heat exchanger = Carbon monoxide = death, no amount of insulation will cure that.

AMEN

The insulation is a good point & a heat pump is certainly worth looking into.

Thanks everyone for your thoughts. I don't know how this furnace has lasted as long as it has, and I imagine that anything new likely won't live half as long as this one.

Anyone know who absorbed Holly / Siegler so I can call their engineering department and offer this thing to them as a museum piece :rolleyes: ?

Yes the current furnace has a standing pilot, so a new unit with electronic ignition would cut gas usage considerably. For modern furnaces, where is the proverbial "sweet spot" in price vs. performance and economic gains with regards to efficiency and single vs. multi-stage? Does it even make sense to consider a multi-stage unit in a climate like Southern California?

The house leaks air like a sieve, so I would be curious whether a Manual J would actually show a smaller unit being able to keep up. That said, adding insulation and/or replacing some of the single-pane windows would probably reduce the heat losses considerably.... I'll be sure to look for the supporting Manual J calculations when soliciting bids.

As for the weather, yes it's quite warm inside and out from May - September around here. Air conditioning would be great but it wasn't standard around here in 1961 homes, so none of the ducting in this house is designed for it. That being said, I'm not sure I want to spend a fortune on electricity by adding A/C to this house.

With regards to possibly replacing the furnace with a heat pump, would a heat pump in this area still require emergency heat from electric coils or a gas furnace?

Also, my electric rates are astronomical while gas is ~ $1/therm. Based on the following rates and the fact that the family typically consumes 300% of "baseline" electricity (making my average cost per kilowatt hour ~ $0.24 or worse), is a heat pump still economically viable? Also, does any manufacturer make a natural gas heat pump or are they solely electric?

http://i829.photobucket.com/albums/zz220/Jason986/elec_rates.jpg


To make a potential decision regarding when to replace the furnace more murky, there is a home warranty policy on the house that covers the existing furnace. While I have no intention of using the home warranty's HVAC company of choice to replace it, I can get a cash-out value from the insurer to apply towards a new furnace from the competent installer of my choice if the current furnace is declared unrepairable.

Given that the only component in the current furnace that's not replaceable is the heat exchanger (or the cabinet of the furnace itself), are there any tests I can request the tech I have coming out (who is not affiliated with the home warranty people) perform on the exchanger besides a careful visual inspection and looking at changes in the flames on the burners when the blower kicks on to detect minute cracks in the exchanger?

While I don't want a safety hazard in my home, I'd be able to purchase a much better replacement unit if I could collect on the home warranty on the current one before tearing it out.

A good tech will use an electronic combustion analyzer to test the flue gases in each of the cells before they are diluted with ambient air via the draft hood. He/she should take readings from each cell prior to and after the fan comes on. A change in readings after the fan comes on is a strong indication of a defect in the heat exchanger.

A heat pump is sized for the cooling load which in your case is probably higher than the heating load. If that is true, the only electric heat you would need would be that which is required to prevent "cold blow" when the heat pump goes into defrost mode. Heat pumps can be set-up with a fossil fuel kit & gas furnace for when the temps drop below where the heat pump alone can handle the heat loss.

For your location, it probably would not be worth the extra investment to upgrade to a more efficient furnace beyond the basic 80% models.

(Caution: Very long post. Move along if you like, otherwise please bear with me...:coffee:)

After speaking with a number of local contractors regarding replacement of the furnace, I have narrowed the field down to bids from three companies. As the cost difference between an 80% and a 95% furnace is negated by the federal tax credit for energy efficiency, all bids are for 95% AFUE two-stage (or better) furnaces. Most ducting will be replaced to allow for proper air flow / static pressure and for the ability to add air conditioning down the road. The following is a spreadsheet outlining each proposed system:

http://i829.photobucket.com/albums/zz220/Jason986/furnacecomparison.jpg

* = no registration required in CA
** = Lifetime primary and secondary on the part, secondary heat exchanger also has 20 year labor warranty
*** = Lifetime primary and secondary on the part only
**** = Wasn't in original bid but is assumed to be ~$600 for sake of comparison


Some observations and questions:

Company A spent over two hours reviewing the attic, crawlspace, and conditioned areas of the house on the initial visit. Companies B and C spent roughly one hour on site. The other contractors spent anywhere from 15 minutes to an hour at the house.

All three contractors will do Manual J and Manual D calculations once I award them the contract, but not for the initial bid. The initial bid for each is a guaranteed maximum price, so if the load calculations show a larger furnace is required, the contractor will cover it.

Company A proposes to relocate the furnace to the crawlspace due to space limitations in the current location (when larger ducts are added) while Company B and C will use the existing utility closet. While outside temperatures very rarely hit freezing here, with the furnace in the unconditioned crawlspace, is there a potential problem if the outside temps fall below freezing?

All three companies believe the house will require a five ton air conditioner when A/C is added down the road. As a result, the furnaces are sized to allow for this cooling capacity. The two Trane contractors indicated that Trane does not make a 95% furnace smaller than 120,000 BTUs that can support five tons of cooling. Thus, the furnace will be oversized.:wall: They countered that because the furnace has multiple stages, the effect of this oversizing would be minimal. Contractor A believes that 80,000 BTUs of heating will be sufficient, but specified 100,000 BTUs for option two because the 80,000 BTU model in that series fails to qualify for the federal tax credit.

On the middle level of the home, the existing ducts are in the crawlspace and the registers are in the floor close to the windows/exterior doors. This level has the living room with the 18' ceiling; the remaining rooms (kitchen, dining room, and breakfast nook) have 8' ceilings with attic access above them. Contractors B and C will replace the ducts with larger ones, enlarge the return, and leave the supply registers as they are. Contractor A proposes to remove the existing ducts and abandon the existing floor registers. He would then install new ducts in the attic, with supplies in the ceiling for the rooms with attic above them and 8-9' up on the 18' high wall of the living room. While heat rises, Contractor A feels that with the registers adjusted properly, his proposed arrangement would be superior to the existing setup. Given that this entire floor heats more slowly than the rest of the house now, is Contractor A's design likely improve things here? Or is the less invasive approach offered by Contractors B and C more sensible?:confused:

Additional Questions:

Which is better in a heat exchanger--stainless steel or aluminized steel? Why?

Is there a preference between a gravity drain or a pump for the primary condensate line?

While I imagine pricing is very regional and job specific, do the quotes from these contractors seem reasonable? Or, are they off the charts?

As the house is a tri-level, Companies A and B have recommended creating three zones at an added cost of about $3000. The theory is that this will allow for heating of the occupied areas only and reduced operating costs, particularly when A/C is added later. Does this sound logical? Does anyone here have zoned systems in your home? If so, how do you like them? Or is zoning a troubleshooting and maintenance nightmare down the road?

Companies A and B have suggested hiring a third-party HERS or CHEERS rater to evaluate the house and its ducting system after the new system is installed to ensure everything is performing well, to provide payback period estimates for other energy saving options, and to comply with state law (http://www.energy.ca.gov/title24/changeout/2005-08-02_NEW_DUCT_REQUIREMENTS.PDF). Company A also recommends having the rater test the existing furnace system to quantify inefficiencies in the current system and to verify that the sections of duct work to be reused do not leak excessively. The estimated cost per test is about $250. Has anyone here performed one of these evaluations or know if the results of one are actually valuable? Does it make sense to test before, after, or both before and after replacement of the existing system?

What other questions should I be asking the contractors before selecting one for this job?

If this were your house, based on everything above, which company / proposal would you select and why?

Apologies for the long, convoluted post and THANK YOU for any advice you can offer!!

I suggest you do your own Manuals J & D. This keeps the honest people honest. I can't imagine a southern California house needing even 80K of heat. They are taking the easy way out by not sizing the furnace correctly & using 2 A/C units. It will cost more upfront but long term you will recover the initial investment, plus.

Here is a link to a program you can lease to do your own calculations. HVAC Software, HVAC-Calc for Heat Loss, Heat Load Calculations (http://hvaccomputer.com)

I am not a heating/cooling expert, but have bought a few homes and furnaces through the years in addition to inspecting many for pre-listing and purchases.

An old heat exchanger with signs of cracks is nothing to put out of your mind. A heat exchanger can crack quickly (usually at night when the temps go down and a little heat is needed), but the result is frequently deaths unless you have dedicated pets. CO is a hidden killer.

After living in So. CA, it is not necessary to go to the cost of a high efficiency furnace (80% is good enough) because the heating load is not that great and you can probably avoid the problems/costs of venting a 90+ efficient unit.

I live in Minnesota and have a 1500 sf 2 level townhouse (quad) with two huge sliders (one on each level) big windows and reasonable insulation. I bought a 80% efficient unit from a good dealer/installer, and opted for a variable speed fan. The good installation made everything work better.

The results were that I have never had a total monthly gas bill over $100 for hot water and heat including taxes and service charge. - The bonus is that my air conditioner operated more efficiently even though I have a very simplistic thermostat that allows the furnace/air handler to do its own job.

I know I can get a better thermostat once I decide to and program it to be customized, but I just have not gotten to that yet, since the savings probably not that great for our climate and our variable schedules. - I just have a lot of thermal inertia in the mass/soil around me, so temperature swings are not a factor.

The big thing for me was the safety with an old furnace that had signs of cracks. The choice for the 80% unit was my past heating cost was not that great and I could use the existing venting instead of getting into venting a double pvc system out the side, which would not look good and upset the interior drywall finishes.

An old heat exchanger with signs of cracks is nothing to put out of your mind. A heat exchanger can crack quickly (usually at night when the temps go down and a little heat is needed), but the result is frequently deaths unless you have dedicated pets. CO is a hidden killer.




Well, I disagree with using the word "frequently." If people with cracked heat exchangers were frequently killed by them, millions would be dead tomorrow morning.


While cracked heat exchangers CAN be lethal, they can also go on for years without causing harm.


You actually have to have two problems to be killed by carbon monoxide with a modern furnace:

1) You need to have a crack or defect

2) You need to have a furnace that's making a lot of carbon monoxide.

Most of the time, furnaces produce very little carbon monoxide, and even if there is a crack it's not an actual hazard.

However, a furnace with a crack that is blowing air onto the burners (fan interference) can cause CO to be produced from burners that otherwise would not make CO.


Finally, modern furnaces that use an inducer motor protect people from plugged chimneys that used to vent combustion gasses into houses through the draft diverter. I found quite a lot of those in my years as a furnace repairman, and if the burners were making CO that could be deadly. Modern furnaces with inducer motors pretty much eliminate that risk.

Prudence dictates shutting off a furnace with a cracked heat exchanger. But usually they still aren't going to kill people. You never know, though.

And I might add that if one person's house leaked like a seive, that actually might cost them money, but possibly save their life, over someone who lives in one of those super energy efficient houses that can barely breathe.

Some people would be will to let is slide and not replace because of the safety if they do not have their family in the house.

Common sense says that a 50 year old furnace is well beyond the time when it should have been replaced, especially if it shows signs of a cracked exchanger. I replaced my latest one that was only 28 years old, but had signs of cracking. My CO meter did not show a reading, but a better meter did show there was some leakage and you could see how it varied with the operating time, temperature and expansion. Cracks only get worse and than can happen dramatically.

My wife and I were gone all day, leaving our cats at home. At night, when the furnace is running and everyone is sleeping is when the problems can arise. - It was a "no-brainer" to replaced a 28 year old furnace, since I had to live with the possibility. With a 50 year old, you have to just be lucky.

I guess keeping the windows for fresh air at night in January when it can be -30F is an option, but not too intelligent.

Common sense says that a 50 year old furnace is well beyond the time when it should have been replaced, especially if it shows signs of a cracked exchanger. I replaced my latest one that was only 28 years old, but had signs of cracking. My CO meter did not show a reading, but a better meter did show there was some leakage and you could see how it varied with the operating time, temperature and expansion. Cracks only get worse and than can happen dramatically.

My wife and I were gone all day, leaving our cats at home. At night, when the furnace is running and everyone is sleeping is when the problems can arise. - It was a "no-brainer" to replaced a 28 year old furnace, since I had to live with the possibility. With a 50 year old, you have to just be lucky.

I guess keeping the windows for fresh air at night in January when it can be -30F is an option, but not too intelligent.


Well concrete, I disagree with your theory and methods.

If you are trying to infer that there is a crack in a heat exchanger because of CO reads, you are using a poor method.

A heat exchanger doesn't have cracks because it's 28 years old, or 50 years old or because it has "signs," it has cracks because it has CRACKS, or holes.

Unfortunately, 'way too many heating "repairman" are out condemning equipment because it's "too old," not because cracks or holes have been observed.

Too many repairman see a $100 dollar commission when they look up a heat exchanger ---- the amount they will collect if they "see" a crack.

Sorry, I'm not impressed with your post or reasoning.

I never said I was an expert, but was offering an opinion to a DIYer on what to do with an old furnace that probably has been lightly used, but may have had some fatigue. I do have a little bit of and experience background with 45 years as a registered engineer, inspected a couple thousand homes (part time over the last 10 years).

If you read my response closely, you might see what I was trying to convey since i have written many technical reports to non-technical people.

I have also torn apart a few furnaces to get a good look at the complete exchanger (without external scopes, mirrors and lights) and am aware of the recent reports pointing out the classic "problems" of some furnace models furnaces and even some of the old pulse units. A 50 year old unit is not even listed in most reports.

The term "frequently" may be a little strong, but depending where you are it can be very common in the cold winters when the furnace is stressed periodically. Cracks are a sign or weakness and a future failure point that can be recognized and should be pointed out. We have numerous deaths in our area every year due to CO and exchanger failures.

When I bought my townhouse, I inspected the furnace and did not like what I saw, but kept it in mind that the furnace was about done for. Just for education and entertainment, I called out a company to check out the system. Everything was OK until he saw the exchanger and put a red flag on it. I illegally removed the flag and called three other reputable companies and began illegally collecting red flags with the same opinions. I ultimately bought a new furnace with a first class installation (the most important item). I also had to get a notarized certificate to get the furnace for donation to a firm to use as an example for examining and instruction.

My CO meter was only a cheap $300 unit, so I called a friend that likes toys and we ran tests periodically over a few days with his high tech toys.

I offered the opinions to a DIYer based on personal opinions, recognizing the different location/weather, but suggesting you cannot gamble with human lives on a 50 year old tin box. - The is no price you can put on life or the long term problems that can occur. I would not gamble my life on a suspect unit that was only 28 years old, especially when you consider the economics and efficiency.

Dick

First of all buy and fit a carbon monoxide sensor under the boiler with a loud alarm.
Do this now.

There were roughly 308 million people in the States in October 2009.
Aproximately 170 people die each year from carbon monoxide poisoning.

Most sitting in their cars.

You are lucky that your boiler is in a separate room, as fresh bread and several other things used in a kitchen are inclined to set these alarms off.
Fitting the alarm will give you peace of mind and will confirm if the boiler is leaking carbon monoxide or not.
While stainless steel heat exchangers are not perfect, they are as close as you can get these days and they last for years, where other types of heat exchanger can burn through.
Zones:
It is normal to run one's bedrooms at a lower temperature.
Therefore, having two zones makes sense.
However, the key thing about zones is that each requires one or more temperature sensors.
You need to consider the situation of the home, the size of windows the effect the sun will have on the home. The sun will make a considerable difference to the running cost.
With the temperature gauge in the wrong place, say on the cold side of the home, the heating will be on longer.
With it on the sunny side, the North side can be too cold.
Trying to get the location of a temperature gauge right, with the right outcome can be a hit and miss affair.
Buying wireless temperature gauges is the perfect solution.
You can move it around to get the right result.
My home has in effect three zones,two the living area and the bedrooms have their own wireless thermostats the bathroom and toilet are both joined to the other zones to ensure they are always warm.
While I am writing this our living area thermostat is sitting on a coffee table by my side - this ensures I am always in an area roughly 70/72f. Regardless of what's going on outside.
If you have temperature gauges fitted against walls, then the temperature of the wall will influence the temperature of the room, a cold outside wall will have the heating running longer.

It is a fact, heat rises. The best and most comfortable form of heating is low temperature under floor heating, this keeps your feet warm and creates a wonderful ambiance.
Moving the heat source up in the air, only works if the heat source is radiant, however this can lead to irritation if one's head is too hot.

The next best is baseboard heating, where the heat rises all round the perimeter of the room and as it rises warms the surface of each wall turning each wall into a medium temperature heat store.. In colder areas this can mean that the full size of each room may be used to maximum effect, whereas other forms of heating lead to cold exterior walls and in practice reduce the usable area of the room by about 18 inches.

High level heat sources mean cold feet and very hot ceilings. Unless you blow the heat back down again and this leads to uncomfortable living conditions and increased cost.

With the boiler being located in the crawl space, then radiant and convected heat is lost to the sky. This is not good practice. The heat you are paying for needs to be contained in your comfort zone. Only go down this road if the boiler is contained in an insulated space, where the insulation is at a minimum five inch thick polystyrene and all the radiant and convected heat is channeled into your living space.

One has to assume that as much of this installation as possible is located within your comfort zone. Any external parts will be correctly put together and properly insulated.
And you will need to conduct your own personal inspection to ensure that this has been done.

It is estimated that there are in excess of 18 million homes in ten States where heating/cooling has not been installed correctly and is causing a problem – usually condensation.

The purchase of an infrared temperature gauge, that you can use to check for leakage and poor assembly will be well worth while.

Keep in mind my earlier blog regarding insulation.
If as I expect your boiler is OK.
Then you should spend your time and money insulating your home.
First of all check for air leaks in the structure.
A small leak about 3/8 ths diameter can strip the heat from a home on a windy day.
Light fittings, switches, pipes through walls, all these cracks and gaps can and will make a home expensive to run and uncomfortable to live in.

Use that infrared temperature gauge to find where your heat is going.
Wood is not a good insulator and it does conduct a great deal of heat into your home in the summer and a great deal of heat from your home in the winter.

As an update to the saga, Contractor A's bid was selected and the furnace and ducts have been replaced. Room-by-room load calcs showed a total heat loss for the house of 75.2k BTUs, so a 95% AFUE 80k BTU furnace was used.

Upon removal, the old furnace was disassembled and the heat exchanger examined. Sure enough, many of the spot welds holding the sheet metal baffles of the exchanger together had given way. Two of the welds had actually ripped through the exterior metal of the exchanger when they failed, leaving a pair of holes 1/8"-3/16" in diameter in the side of the exchanger.

Needless to say, I'm glad the decision was made to replace this thing. The savings on gas by going to a smaller furnace and zoning the house probably won't hurt either :D.

Now I have to go after my home warranty company for failing to detect the holes in the exchanger and for denying my claim on the furnace even after their agent inspected the failed exchanger once it was removed from the furnace....

I certainly hope you didn't let some smooth talking salesman talk you in to zoning that new furnace. If you did, I strongly urge you to lock the zone dampers open. If the furnace is sized for the whole house & you are only supplying air to half of it, that furnace is going to overheat & destroy itself.
Zoning a single stage furnace is one of the worst things you can do to it.