Forced Air Furnace Systems

John Owens Services has been active in the installation and servicing of all types of furnaces in Marin County since 1994. Our most popular brand of furnace is Trane. We have been a Trane authorized dealer since 1994. We also represent Day and Night, Rinnai, Payne, Bryant, and Bosch furnaces.

How long should my furnace last? and when is it time to replace it?

Of course, we all know that things are not made to last as long as they were fifty years ago. The problem being a fifty-year-old furnace is very inefficient. It could be wasting a lot of the  gas going straight up the flue pipe and not using that energy to heat your home. Very old furnaces are usually forty of fifty percent efficient. They waste up to sixty percent of the energy used. Now we install ninety seven percent furnaces that only waste three percent of the energy used.

All furnaces eventually corrode and crack. Why is this a problem? Well, a furnace is really a Tin Can with a flame inside and we blow air over the can to warm the air and warm the house. The Tin Can or core of the furnace is actually called a heat exchanger and when it cracks the products of burning gases (combustion biproducts) pass into the air that we breathe in the house. This could lead to health problems, headaches or even death through carbon monoxide poisoning. Since 2010 carbon monoxide detectors have been required on each floor level of a house. Most people are unaware of this. PG&E recommends using carbon monoxide detectors on any gas furnace over fifteen years old. Fifteen Years is about the point that the metal in the heat exchanger has been stressed thousands of times and could be prone to cracking and cause leakage into the home.

Many furnaces in Marin County are twenty-five to thirty-five years old (the serial number can indicate the date). When these furnaces were new they were only seventy five percent efficient. Over time through wear and tear and mineral build up and corrosion they are probably only fifty to sixty percent efficient. When we go to repair one of these older furnaces we always make the homeowner aware that the $600 repair may be only the first of many on a furnace that could fail or crack at any moment, and it may be a better option to replace the furnace. I am sure you would get the same advice from a car mechanic working on a 1980’s car.

The good money after bad syndrome.

There is an analogy in the heating industry that your furnace runs 75,000 miles every winter. The ignition system, gas valve, blowers, and circuit boards start and stop hundreds of times perhaps thousands every winter. We can surmise that a thirty-year-old furnace has over 2 million miles on it (2,250,000 miles). No one would drive a car with 2 million miles on it. They would replace it. People don’t go looking at their furnace or water heater very often. They are never particularly attractive to look at anyway. When we eventually pull the old furnace out into the driveway people always comment “ I cannot believe we kept that rusty piece of junk for all these years”. Yes all good things including ourselves wear out.

How many types of modern furnaces are there?


Up-flow gas furnaces blow air upward usually into the attic ductwork

Down-flow furnaces blow air downward usually into the crawl space ductwork

Horizontal furnaces are usually located in the crawl space or in the attic


Older furnace were one stage of heat and one blower speed. That’s because they were designed for the coldest day of the year when it is 30F outside. This is a mild California climate and most of the time we only need half of that size furnace.

Single stage heat and blower –  made in low and high efficiency. They are used in commercial applications, apartment buildings. In these situations, lower energy efficiency, lack of comfort, or louder noise don’t usually play into the selection.

Two stage heat and two stage blower – made in high and low efficiency. The furnace always starts at low heat and low fan. When required it jumps up to high heat and high fan. This type of furnace will stay on longer without short cycling. It will increase comfort and lower energy bills. It has a standard inefficient blower motor.

Two stage heat and two stage blower – made in high and low efficiency. The furnace always starts in low heat and low fan. When required it jumps up to high heat and high fan. This type of furnace will stay on longer without short cycling. It will increase comfort and lower energy bills. It has a standard inefficient blower motor.

Modulating. Furnaces that are multistage heating and multi stage blower. Modulating furnaces ramp up or down according to the amount of work to be done. They are exceptionally good in zoned systems where the load varies greatly.

Blowers and Fans

We still have single stage conventional blower and fan motors that use large amounts of electricity and are loud at start up.

For more than 20 years we have had ECM variable speed motors and blower motors that use about one fifth the electricity of a conventional motor. A controller can ramp the speed up and down on starting and stopping to make the sound almost unnoticeable.


The lowest level of efficiency is 80%. This type of furnace goes into a conventional metal flue pipe and it does not produce any condensation.

Condensing or high efficiency furnaces are in the 95 to 97% efficiency range.

These furnaces vent into PVC piping and they produce condensation (above 84% efficiency the flue gases are much cooler and the byproducts have a lot of water vapor. Conventional metal flue would rust away that is why we have to use PVC, and the dripping condensation goes out through a small PVC pipe)

So what are my choices?

80% single stage heat and blower – Very basic

80% two stage heat two stage blower

80% two stage heat two stage variable speed blower – Popular 2 stage and quiet

95% single stage heat and blower –  Basic high efficiency

95% two stage heat two stage blower

97% two stage heat two stage variable speed blower – most popular high efficiency, 2 stage, quiet variable speed blower

97% modulating heat modulating blower – Top of the line very popular with zone systems and multistage cooling.

Hydronic furnaces are another option. This is a furnace which is heated by hot water from a water heater or a boiler. There are advantages to not having a flue, gas line, condensate drain, in an attic or crawl space. These are items that may require maintenance in the future.  Some multi-level homes may have multiple hydronic furnaces running from one heat source which leads to greater efficiency and lower maintenance costs.

Direct Vent Wall Furnaces are another option. We use these to heat small apartments, art studios, work spaces, room additions. They are very efficient with built in programmable thermostats and require no duct work.

Energy Efficiency Verification

The State of California maintains energy standards for heating and cooling equipment. Installations are now required to have independent third party testers who verify that our installations meet mandatory standards (a Hers Rater or tester – is a person who is a Home Energy System Verifier). Hers testing is required by all Cities in Marin County.

When a furnace is replaced it is now mandatory that a third-party tester pressure tests your duct work to ensure it is within acceptable standards.

There is good merit to this system. PG&E research shows that the average duct leakage into unheated space is 34 percent. That is average. What would be the point of installing a 97% efficient furnace only to through 40% of the energy away under the house or into the attic.

We pre-pressure test our furnace and air conditioning systems before the third-party inspector arrives. We evaluate any duct leakage (which is often minor) and do the repairs – saving a second fee for the Hers tester if he has to make a second visit.



We offer a five years parts and labor in house warranty on all heating and cooling equipment we install. This is in parallel with the Manufacturer’s warranty which often does not cover labor.


We have been selected to offer Government Supported financing for energy upgrades through the PACE program. Property Assessed Clean Energy (PACE) is a means of financing energy efficiency upgrades or renewable energy installations for residential, commercial and industrial property owners. This includes water heaters, solar, furnaces, ductwork, air conditioning, insulation, windows, and many other options. This up to 20 years long term financing paid through your property tax bill requires only 3% equity in your home to qualify, it gives a tax break, low monthly payments, and energy savings ( not based on credit scores ).

We also offer conventional with a 12 month same as cash with no fees, or 84 month conventional term financing.

Learn more about Renew California First and GreenSky Financing!


Give us a call 415-450-6707 or email a request for an estimate

Call us today for an estimate for a new furnace system installation or call to schedule an annual preventive maintenance checkup of your existing furnace.



Fields marked with an * are required
Read Our Online Reviews

Located in Marin County, John Owens Services, Inc. has 30 years experience in licensed repair and replacement of boilers, radiant heating, HVAC, electrical, furnaces, plumbing, and is an authorized service provider of Rinnai products.