BRRRRRRRR Momma, why ain't the heat on yet!?
January 11, 2012 10:49 PM   Subscribe

What are the advantages to a newer modern gas furnace heating system vs. a 35~ year oldish pilot-light gas system?

Admittedly the last time I looked this up I found the costs to be high to the point of ignoring the need, but recently the pilot-light parts to our current heater went bad and had to be replaced by the local utility (nice guys!).

Our current home heating system is some 35 years old, gas furnace with a millivolt thermostat... The utility guy mentioned we actually had the wrong type of thermostat? (huh?) We are currently not getting adequate voltage to the heater to active the system (something with the wiring). This is expected to cost some $100~ to replace. We also were asked to make an adjustment in the furnace closet to meet newer earthquake standards.

This time I've been looking at what is available and I read a few HVAC questions here, but I also want to shoot out to the general question to the hive mind. I live in Southern CA though, and in our climate and our old house (3 bed 2 living 2 bath) we have no AC (ocean breeze) and only really the heater is set for use at most in some weeks of 3~4 months of the year. Only in the last few years has this area been regularly cold enough for modest weekly usage during the fall and winter.

Is it economical to consider a modern furnace?
posted by Bodrik to Home & Garden (9 answers total)
New furnace will be more economical in its use of gas - maybe as much as 25% more eficient. Also, should need fewer parts than you existing system over the next ten years, after which I kind of expect your existing system would be totally shot.

You don't say if your system is radiators or hot air, but a new hydronic (radiators) system could run around $7000 installed, I would guess a hot air would be about the same.

So there's some math to do about costs.

Ask your utility about underwriting the new furnace, maybe the state has tax breaks for installing efficient heating.
posted by From Bklyn at 11:29 PM on January 11, 2012

Electricity usage! I live in Canada. Our old furnace was a high efficiency gas furnace, even though it was about 15 years old. I was shocked when a heating technician measured the FAN power as being about 1000 watts (yep, one thousand).

We recently replaced the furnace and got air conditioning, also. The new furnace has about the same gas efficiency as the old one, but the new one uses far less electricity to run the fan. Up here, I've seen advertisements that state your electricity savings will be about $250 per year. That's electricity savings on a GAS furnace. So the new furnaces have way more efficient fan motors than the old ones.

Having said all of that, it seems that you use your furnace (heating only) very rarely, and alas, I must leave you in the same lurch: will you use it enough to make up for the savings versus the higher cost of a very efficient furnace? You'll have to decide. My point is to look into the electricity usage (fan) as well as the fuel (gas) usage.
posted by mbarryf at 5:05 AM on January 12, 2012

For that low usage, I would say that it is not economical. You'd have to do the math: how much does your gas bill go up during the heating season, make an educated guess as to the increased efficiency (say 25%) and see how long it would take for a 25% cheaper gas bill to pay for the new furnace. Which might be longer than you will own the new furnace.

I personally wouldn't replace that furnace until it was irreparably broken.

The efficiencies of the newer furnaces are basically this:

Burner technology is better, extracting a greater percentage of the heat from the burning gas and letting less heat go up the chimney.

Multi-speed blower motors and adjustable duty burners. If it is just "chilly", the furnace can run at half-speed and provide better comfort. Because a single speed unit might run at full blast for two minutes out of every 30, and then sit idle the rest of the time. This means you are getting blasted with heat and then chilled out alternately.

They probably run more quietly.

On the other hand, a new furnace might give you some flexibility that you don't currently have. If the current one is particularly inefficient, you might be hesitating to turn it on and suffering through cold spells because you don't want to waste money. A more efficient one might give you the freedom to run it in a more comfortable manner.
posted by gjc at 5:55 AM on January 12, 2012

Your old furnace is probably in the range of 70 to 80% efficiency. Some research as to the specific model might provide more information. A new furnace would be closer to 95%. You can estimate your heat use from your energy bills. If you have gas for stove and hot water just look at the increase during the heating season. You could save 15 to 25% of that expense with a new furnace. How many years would it take to payback the new furnace at that savings? If it is longer than 3 to 5 years it might not pay to upgrade, and in your area I doubt you use it enough to pay it back in ten years.
posted by caddis at 7:14 AM on January 12, 2012

Thanks for the various responses! Keep them coming!

Mbarryf pointed out one thing I forgot about. We noticed the last time we considered replacement that the fan apparatus used a lot of juice as well. For that reason we also were wondering if there was an alternative.

This house has been ours for 20 some years and I expect to eventually inherit as well. I think we would have a heavy net loss initially, but yes we do not the flexibility that we would like... Silently grunting out the cold!

Late yesterday we decided to at least get an estimate from some local folk to get an idea of what is available and better analyze costs.
posted by Bodrik at 9:19 AM on January 12, 2012

If your furnace is 35-years old, it is probably more in the 60% efficiency range. You can get a new furnace that will be about 95% efficient, so expect to save roughly 35% on heating costs, plus the not insignificant, especially in California, electricity savings with an ECM fan motor.

A new furnace should not run you $7K either. Half of that would be reasonable for total cost, especially as you'll be able to use a quite small unit.
posted by ssg at 9:25 AM on January 12, 2012

A problem I ruefully found is that the self-ignition lighter on a new furnace (no pilot, it sparks itself up when needed, new pilot light furnaces are banned here and maybe everywhere?) goes bad every three years or so. ~$200 parts and service call each time. Not far past being out of warranty, of course. And when it goes bad, it is scary bad. Out of sight in the basement, it goes BOOM when it finally sparks up, and that BOOM is a fireball of gas that is let out as it kept sparking and not lighting until it finally lit. It's a common problem and I've had two replacements$ so far. It might have started a fire if there was flammable stuff near it. Standing near it to see what was wrong when it tried to fire up, I saw and heard click-click-click-click-click-click-click-BOOM with a fireball. A light, translucent, gaseous bluish fireball reaching about 2 feet out of the starter area, instantly gone, but scary all the same.

But mine probably gets much more use than yours. Still, if yours is working as a furnace, I think you should keep it as long as you can. Gas is cheap now and for a while longer.
posted by caclwmr4 at 8:37 PM on January 12, 2012

I found out this evening that it is a Holly Forced Air Heater (Model 75UF) from Holly Manufacturing... Now I remember why I didn't decide on much last time. There is essentially zero info on this heater.

I wonder how efficient it really is... but I guess I'll examine a few gas/electric bills. We are trying to get an estimate done to get a touch of local pricing.
posted by Bodrik at 8:49 PM on January 12, 2012

We are going to wait till the summer. Space heaters for now!
posted by Bodrik at 9:03 PM on February 13, 2012

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