Saturday, November 29, 2008

Its January ! - Time to Change Your Air Filter

On home consultation or service visits we sometimes ask the homeowner when they last change their air filter. You would be surprised how often the answer came back as "what air filter?" or "I dunno, last year??"

So I am making a point to anyone who comes across this blog to go and change their HVAC system filter this weekend. If you are in the San Jose South Bay Area you have probably been running your furnace for 3 months by now and this is a good mid-season filter change. The standard 1" pleated air filter costs $5 from the big box home improvement stores and it is the cheapest maintainence you can do to protect your system.

So whats happens when you don't change your filter?

- Your fan blower motor energy consumption goes up because it has to overcome a higher resistance.
- Your AC and furnace heat exchangers get dirty which in turn reduce their efficiencies AND capacities. So the 80% 56kBtuh output furnace that was installed 3 years ago is no longer putting out the same output at the efficiency when it was brand new. Or the 3 ton AC you spent a few thousand dollars on 4 years ago just turned into a 2.5 ton.
- Your ducts get dirtier which in turns blows back out to your house. Like dusting more often??

If they are not good enough reasons, you should not be reading this anymore. :)

Next time we will talk about the various filtration options available to the home owner. Stay tuned....

Do you know your Duct Leakage Rate?

It has been cold and rainy in the Bay Area lately and that means your furnace has probably been running overtime. So whatever inefficiencies in your heating system are amplified from the extended run time. Though the furnace efficiency or AFUE ratings gives you an indication of the unit performance, most homeowners don’t realize that the average duct system is an even bigger source of loss for heating and air conditioning system.

California Energy Commission (CEC) – a California State Government agency commissioned a study a few years ago and found that the average duct leakage rate on existing homes in California is at a staggering 30% (copy of the letter can be found on our website This leakage takes the warm air generated by the furnace and dumps it directly into your crawl space or attic. As a result of the study and a need to conserve energy, the State of California makes it a requirement for all inland regions of California that ducts be sealed as part of any furnace or AC replacement work. It is not a requirement in the San Francisco Bay Area yet and that’s why most contractors don’t do it or mention it to the customer. But if you are concerned about your utility costs and the environment, it is definitely an area to look.

To find out the duct leakage rate, a contractor equipped with duct testing equipment can perform a pressure test at your house. The set up and test take about 1-2 hours. Sandium is currently running a web coupon special for the test at $149. Based on the result of the test we can then determine whether or what action should be taken on the ducts. For residential customers PG&E has rebate of $350 to $600 for duct sealing if the leakage rate is brought below 15% but they require ducts to be tested by a certified contractor before and after.
We have done many tests in the south bay area and what we have found is that houses in Los Altos, Los Gatos and Saratoga area sometimes have a higher leakage rates than others. That is mainly because those houses were generally built 50+ years ago and have underfloor metal ducts that in many situations are rusted out. In those types of cases we recommend replacing the ducts. And for new ducts installation we can usually keep the leakage rate below 6%.

Options to Tackle High Heating Bill

Most of the homeowners in the Bay Area have probably had their furnace running for a few weeks now. This is about the time when the first heating bill arrives for the season. Obviously the amount will correlate to the size of the home and usage pattern. But it is worth spending some time reviewing if you feel it is excessive for the size of your home. In general if the bill is over $200 there may be opportunity to save that will have a quick payback.

There are a couple places to trim your heating bill. Firstly, if you are not using a programmable thermostat you should strongly consider it. Sometimes a furnace is left on when the house is not occupied or when it is not required to be heated. Those can be avoided if a digital programmable thermostat is set up properly. It is relatively inexpensive as a basic thermostat can be had for less than $50 from Home Depot.

Secondly, if your ducts were installed over 20 years ago you should have it checked for leakage. California Energy Commission have done a study indicating that the average leakage rate for older homes is around 30%. That means $0.3 of each dollar is spent heating or cooling your crawlspace/attic. That can be reduced greatly if the system is properly sealed. A duct leakage test can be done to analyze your current status. PG&E also has rebates from $350-$600 to encouraged homeowners to seal their ducts. In certain situations the rebate may be enough to cover the cost of sealing.

Thirdly, if your furnace is over 15-20 years old it may also be a source of inefficiency. There are modern furnaces that are rated at over 95% AFUE. A 20-30 year old furnace is probably running at 60-75% so a significant saving will be seen if it is replaced.

Next time we will discuss more about duct leakage and duct sealing.

Furnace Features - Variable Speed Motor

Third and last on our series of furnace feature discussion, we are going to cover the variable speed motor/fan.

As the name implies, the variable speed motor is capable of adjusting the air flow to fit various duct configurations, heating/cooling applications, and ramps up in ways to provide the quietest operation possible for your duct system. This is in contrast to the older furnaces that has constant speed or multi-speed motors. If special type of filters like electronic air cleaner or high efficiency media filter are desired the variable speed fan is capable of running in a very low speed to recirculate air.

Certain manufacturers also take advantage of the variable speed fan in zoning systems to make air flow seemless for its operation. This is a big plus for zoning retrofit applications.

Furnace Features - Multi-Stage Furnaces

We are now officially in the holiday season with Thankgiving last week. This is the time of the year when we get all the furnace service calls. And if your furnace is older than 15-20 years and is starting to give you problems, you should consider replacing the furnace with one that has features that were not available when the original one was installed.

Speaking of which, we shall continue on the series of articles on residential furnaces. The feature we will cover today is multi-staging.

The older style furnaces are all single staged, which means they operate on their full capacity (eg. 70kBtu/h) whenever they are on. The most common multi-stage models for residential furnaces are 2 stage. They can operate at their full capacity (i.e. high stage) or at a low stage which is roughly half the full capacity.

There are two main benefits to a multi-stage furnace compared with a single stage model. First, the furnace operates at a quieter level. This is the result of the recirculating fan running at a lower speed and roughly half the burners are in operation. Second, the system stays on at longer intervals which keeps the house at a more even and comfortable level. Both benefits are very desirable and in my opinion a very good value from a cost-benefit standpoint.

Thursday, November 27, 2008

Furnace Features - Efficiencies

As you shop for a new central furnace, there are primarily three main product feature consideration you need to make. They are efficiencies, stages of heating, and motor types. Today we are going to cover the efficiency option.
All major furnace manufacturers offer standard efficiency and high efficiency models of their furnace lines. Standard means 80% AFUE which is the minimum requirement mandated by the federal government. High efficiency models can be anywhere in the 91%-96% AFUE range depending on brand, capacities, and model. For comparison, the 30 year old furnace in your closet is probably a 60-70% AFUE model so you will see a drop in gas consumption even by replacing it with the standard model. If you want to save even more the high efficiency models are good bets. However, high efficiency models are not always possible in certain situations because they require a separate flue pipe for the combusted air and an extra condensate line. A licencsed contractor need to survey your existing installation to determine if the upgrade is possible. PG&E and federal government have rebates and tax credit to encourage homeowners to upgrade to the high efficiency models.

Heating Season is Almost Here

Depending of your tolerance for house temperature level you may have turned on your furnace for the season already. Most of you probably haven't used it since early spring. So it is a good time to talk about furnace maintenance. Modern furnaces use electronic ignitors so there is no need for liting pilots. However, the minimum you should do is to change your filter which extends the life of your HVAC equipment and ducts by keeping dusts away. Typically in this area you should change your filter 2 times a year for furnace only and 3 times if you have AC. You may also consider having a licensed HVAC technician do a profession cleaning and check up once a year. They should check all gas/electric connections, operations, and clean the interior compartments of the furnace including the induction motor. For condensing furnaces they should also check the drain line to make sure water drains properly.

If your furnace is older than 20 years we recommend you call PG&E to do a carbon monoxide test on an annual basis. This is a free service from them. Carbon monoxide is an odorless gas that is deadly if inhaled in an excessive amount. For central furnace it comes from gas leaked from the combustion chamber into the air stream. This occurs when the furnace develops cracks in the heat exchanger as it gets old. If an unacceptable level of carbon monoxide is detected you should have the furnace replaced or repaired. Based on our experience the high cost of a replacement heat exchanger part (assuming you can even locate one) for older furnaces makes the repair option unjustifiable.

I hope that helps you get ready for the winter. Next time we will talk about the different features you can find on modern furnaces. Feel free to drop us a line if you have any question or comments.

Home Owner Heating and AC Blog for South Bay

We have decided to start this blog to address a lot of the common questions from homeowners regarding their heating, cooling, and ductwork systems. I am a mechanical engineer by training and have been in the HVAC industry for over 20 years. We are a licensed mechanical contractor based in Sunnyvale CA serving the whole south bay area. We welcome questions and comments on the topic of residential HVAC. You can email them to us at or post them from this blog site. We will be adding answers and short articles covering relevant topics from time to time.

See you around...