Author Topic: HVAC maintenance and replacement questions  (Read 553 times)

Beach_Bound

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HVAC maintenance and replacement questions
« on: November 27, 2018, 08:44:47 PM »
I had my gas furnace "tuned up" today, and have some questions where input from the hivemind would be very helpful. Some background info: both the furnace and air conditioner are 18 years old, original to the house. The AC hasn't had any issues in the past 7 years, since I've owned the house. The furnace has needed repair twice in that time: the first time the sensor was too dirty to see the flame (learned my lesson there - won't pay for that again), and the second time the electric starter failed and needed to be replaced. No problems other than that. On to the questions from today:

1. The technician used a camera scope and blacklight to look for bacteria in the system. This was in the coil area, above the burners. There was definitely some growth in there. The company sells a UV light system that will keep the area clear of bacteria for around $1000. That area is warm and dark - of course bacteria want to grow there. The technician didn't recommend buying the UV light for an old system if I haven't been having any health problems (and I haven't). Points to him for honesty. I'm not buying a UV light for this system, but I'm curious if others have heard of them in HVAC systems? Useful new technology, or gimmicky sales opportunity? I've tried googling it, but everything I read seems to come from people selling the technology.

2. There's a very very small gas leak in the gas valve. It was only detectable by the technician's sensor when it was <1cm away from that specific corner of the valve. From what he said, it sounds like internal gaskets in the valve slowly fail over time, and it could have been like that for years. I used a different (worse) company for a tune up 2 years ago, and I'm pretty sure they didn't use a sensor to check for gas leaks. The quoted cost for replacement was around $800, which sounds insanely high for a component that appears to cost around $200 online. The technician suggested buying a combustible gas sensor for the basement where the furnace is located rather than spending $800 on an 18 year old system. The combustible gas sensor sounds like a good idea regardless of whether I get that component replaced. Should I live with the small leak or replace it? Is it possible to patch it without replacing the component (technician said no, but maybe there's a DIY coping solution)? If I do replace it, I'd definitely shop around for a better price.

3. Both the furnace and AC are 18 years old. Google suggests AC typically lasts 15 years and furnaces 20 years. Looking around the houses in the neighborhood, it looks like most people have replaced their AC. On the other hand, the furnace looks to be burning well (blue flame), the heat exchanger has no cracks, and the measured efficiency is 80%, which matches its rating. I live in the mid-Atlantic. It gets hot but not unbearable in the summer, and I'd be ok if the AC broke. It gets cold enough in winter though that I can't delay heater repairs without worrying about freezing pipes. With all that in mind, does it make sense to proactively replace the HVAC system? Or just do repairs on the furnace as required, and replace the whole thing when the AC eventually goes? I'm getting some quotes now, just to have the info.

4. I'll probably need a new HVAC system within the next 5 years. What kinds of questions should I be asking when I get quotes? What features are worth paying for, and what are just headaches to maintain? I'm thinking I want something mid-range, single stage, single blower speed. I use little enough energy (450 therms for heating total over last winter) that the extra expense of a fancier system probably doesn't make sense for me... right? I'm struggling to find good resources online that aren't trying to sell me something.

tyler2016

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Re: HVAC maintenance and replacement questions
« Reply #1 on: November 28, 2018, 04:58:36 AM »
If you are planning on staying in the house, I'd replace the system. I bet your A/C cost is higher than your gas cost. More than likely you are on a 10 seer system. A new 16 seer system would remove 60% more heat per watt.

Get several bids. When I replaced my system this summer, the bids ranged from 5500 to 13000. You get what you pay for, but the what isn't always what you wanr. Sometimes the what is TV ads, fancy offices, fancy vans, etc. I went with the lowest bid because the company kept costs low. The owner showed up to bid on the job in a Yaris, and emailed a PDF, while the other companies showed up in big vans and gave me fancy folders with printed brochures that told me less than the cheap guys PDF.

Make sure your system is sized correctly. A lot aren't.


Acastus

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Re: HVAC maintenance and replacement questions
« Reply #2 on: November 28, 2018, 10:50:19 AM »
The money question is how long will you stay in your house? If is it only a couple years, then replacement will not pay off. Otherwise, it is worth replacing your furnace. New gas furnaces have up to 95% efficiency, so you will get almost 20% more heat for free.

The A/C is less obvious. If summers are long, then it may be worth it. If you live up north, it probably won't save enough quickly, so it is better to wait until it fails. An 18 year old system uses old, ozone depleting refrigerant. It would be best to change the lines when you change the system, because new refrigerant is not compatible with old R11 or the compressor oil the floats around the system.

Full disclosure - I retired from Carrier, an HVAC manufacturer.

Jon Bon

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Re: HVAC maintenance and replacement questions
« Reply #3 on: November 29, 2018, 07:33:26 AM »
Ok first off 18 years is old for a AC, and relatively old for a furnace. You do probably have contractor grade stuff, but if they have been maintained decently they might have life left.  However it sure sounds like that furnace tech was trying to up sell you. I have never heard of a UV  light to prevent bacteria in a furnace. I think I have like 7 furnaces now and have never heard of such a thing.

The gas 'leak' too, sounds like them trying to up sell. Gas stinks, if you have a leak you will know it. If you want to get very sure use a spray bottle of water and dish soap on all the joints. If you see bubbles that is a leak. Sounds like he was detecting a pretty much undetectable leak. My worry level on this one would be about a 1/10.  Sounds like he was looking for a leak and found one, reminds me of the roofers who offer free inspections, then pull a few shingles off your house so that they can repair them!

I also think the 'savings' on new HVAC is highly overblown. Yes you will  use less gas and electric but the savings are not going to be 20%.  Most Utilities charge a substantial fixed rate every month just to be hooked up to their services and then usage fees on top of that. So A typical gas bill for me might be $100, but only $70 is for usage. So the savings would only be $14 a month.

That is a VERY long payback for a $3000 furnace!

OK I did the math with discounting, saving $168 a year (14*6) it will NEVER pay itself off. Even keeping it for 30 years it only saves you $2800. Granted you need a new furnace at some point but simply upgrading just for efficiency the numbers dont work. You might have a higher gas bill or a different fee structure so the numbers might be slightly different. But my point remains valid, the 'savings' by upgrading are just not there.

Full disclosure: I have a great HVAC guy who puts me on top of the list every time. So I am never in danger of a no heat emergency 4x the price bill. That is also something to consider.





tyler2016

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Re: HVAC maintenance and replacement questions
« Reply #4 on: November 29, 2018, 08:11:28 AM »
Ok first off 18 years is old for a AC, and relatively old for a furnace. You do probably have contractor grade stuff, but if they have been maintained decently they might have life left.  However it sure sounds like that furnace tech was trying to up sell you. I have never heard of a UV  light to prevent bacteria in a furnace. I think I have like 7 furnaces now and have never heard of such a thing.

The gas 'leak' too, sounds like them trying to up sell. Gas stinks, if you have a leak you will know it. If you want to get very sure use a spray bottle of water and dish soap on all the joints. If you see bubbles that is a leak. Sounds like he was detecting a pretty much undetectable leak. My worry level on this one would be about a 1/10.  Sounds like he was looking for a leak and found one, reminds me of the roofers who offer free inspections, then pull a few shingles off your house so that they can repair them!

I also think the 'savings' on new HVAC is highly overblown. Yes you will  use less gas and electric but the savings are not going to be 20%.  Most Utilities charge a substantial fixed rate every month just to be hooked up to their services and then usage fees on top of that. So A typical gas bill for me might be $100, but only $70 is for usage. So the savings would only be $14 a month.

That is a VERY long payback for a $3000 furnace!

OK I did the math with discounting, saving $168 a year (14*6) it will NEVER pay itself off. Even keeping it for 30 years it only saves you $2800. Granted you need a new furnace at some point but simply upgrading just for efficiency the numbers dont work. You might have a higher gas bill or a different fee structure so the numbers might be slightly different. But my point remains valid, the 'savings' by upgrading are just not there.

Full disclosure: I have a great HVAC guy who puts me on top of the list every time. So I am never in danger of a no heat emergency 4x the price bill. That is also something to consider.

I agree on the selling. As far as savings go, it might not be worth it to replace an entire system, but if the system is being replace anyway, an upgrade from a 14 to 16 seer system or an 80% AFUE to a 95% may be worth it. When I replaced my system, I bet on climate change. I bought a basic 80% furnace, but spent about $1000 more an 16 seer A/C system vs a 14 seer system. When I ran the numbers, 14% more efficiency on cooling a slightly growing temperature disparity is about a 5-7 year break even point on my house. The stock market isn't liekly to beat that kind of return.

Beach_Bound

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Re: HVAC maintenance and replacement questions
« Reply #5 on: December 01, 2018, 06:57:15 PM »
Thanks all for the input! Jon Bon, I hear you on the upselling - I got the sense that the company's check list for furnace tune ups included a lot of sales opportunities, but the tech himself wasn't completely sold on them. He showed me bacteria growth above the coils, then advised me not to worry about it unless I had been getting sick frequently. He sure did try hard to find a leak though.

Regarding costs, I spend about $500 per year conditioning my house. This number comes from comparing my annual utilities cost to the cost during months that use no heating or cooling, so it's just looking at the marginal cost of conditioning the air, and doesn't include hook up fees (which are significant). Of that $500, roughly $450 is heating, and $50 is AC. (I really don't use a lot of AC). Doing a NPV calculation comparing a new 80% and 95% efficient furnace, I should be willing to spend up to $850 more for the 95% efficiency, assuming a savings of $70 annually, a rate of return of 7%, and a furnace lifespan of 20 years. That's just comparing 2 new systems when the time comes to replace the old one. The math on replacing a functioning HVAC system doesn't work out at all from an energy savings point of view. It might still make sense to avoid the weekend and/or emergency upcharge if my heat goes out in the winter. Sadly, I am not at the top of any HVAC guy's list.

I also found some state-specific rebates on new energy efficient systems. Unfortunately, the process to claim them is pretty tedious. First I'd need an energy audit, then a HVAC contractor has to submit an application for an energy rebate, then the state has to process the application and grant a confirmation number, and only after a confirmation number has been issued can the system be installed. After installation, the contractor has to submit documentation verifying the installation, and that has to be done within 90 days from when the confirmation number was issued.

The incentive is good - $400 for a 94 AFUE furnace or $650 for a 96 AFUE one, and $400 for a 16 SEER AC or $650 for a 17 SEER one. This is tipping the balance in favor of replacing the systems before they fail. I don't think I'll have the luxury of waiting for applications and confirmations if I wait to run the systems to failure. I anticipate some excellent spreadsheets in my future!