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Learning, Sharing, and Teaching => Ask a Mustachian => Topic started by: mizzourah2006 on June 04, 2020, 07:40:53 PM

Title: Getting the AC and HVAC replaced
Post by: mizzourah2006 on June 04, 2020, 07:40:53 PM
Our AC and HVAC blower fan are acting up. We had the repairmen out a few years ago and he said the builder unit was on it's last legs. Suggested replacing the entire HVAC system when we replace the AC as he said that a new AC puts more pressure on older HVAC systems and could potentially shorten the life of a new AC unit.  Not sure if this is true or not.

Our current system is 16-17 years old. We keep our home relatively warm. 78ish during the day and 75-76 in the evenings during summers where it's almost always in the high 80s to low 90s during the days. Our home is just shy of 2.2k sq ft.

So I have a few questions.

1. Should we replace the entire HVAC system or just the AC assuming the rest of the HVAC checks out.
2. It looks like we're in the 3 to 3.5 ton range given our house size. Does the fact that we tend to use the air less than most people mean we can defer to a smaller unit or should we just go with the larger unit?

Appreciate any thoughts.
Title: Re: Getting the AC and HVAC replaced
Post by: Abe on June 04, 2020, 11:21:29 PM
My parents have gone through several ACs in their house and have never had to replace anything other than the AC unit and the heater unit (switched to a heat pump for the latter). Are they talking about replacing the ductwork? If so thatís nonsense. You may need the ducts inspected for leaks to improve efficiency but otherwise if you get an AC with the same tonnage as your old one (or less), itíll be fine.

You may be able to opt for a lower tonnage unit, but it will take longer to change the air temperature in the house. Depending on the amount of insulation in the house and incoming heat energy via windows and roof, an AC that is too small may be on more than necessary and ultimately wear out faster than a properly sized unit. If your current unit was working fine, get a similar size unit with a much higher SEER and youíll come out ahead.
Title: Re: Getting the AC and HVAC replaced
Post by: foghorn on June 05, 2020, 06:35:33 AM
Here is my recent experience.  My home is about 18 years old.  I live in the Upper Midwest where winters can be brutal.   brrrr.

In the Fall of 2019 the AC died on one of the last cooling days of the year.  I got through the winter with the furnace and then had the entire unit (AC and Furnace) replaced in March of this year.  I also had a whole house humidifer added during the installation along with a new thermostat (web enabled, etc.).

I did the whole thing at once as I fully expected the furnace to die soon and did not want to have a second install process in a year or two.  Also, living where I do, the furnace going out when in it -20 degrees quickly becomes an emergency.

I am not sure of the philospophy of replacing both the furnace and AC at the same time.  I am sure others here have a better perspective on that.  I simply wanted to do the whole thing at once and hopefully not think about it for 15-20 years.

Total cost when all done = $10,000.
Title: Re: Getting the AC and HVAC replaced
Post by: ctuser1 on June 05, 2020, 06:51:50 AM
Do you have a single heat pump or something that does both heating and cooling?

Replacing "everything" together sounds like a very alien concept to me. I have a new gas boiler and a 14-year-old Central AC. The two systems are completely independent - the gas boiler heats via water pipes (much better than the dry heat that forced air gives you) and the A/C cools via forced air. The only place where the two intersect is the smart thermostat which controls both.

Title: Re: Getting the AC and HVAC replaced
Post by: 405programmer on June 05, 2020, 08:58:42 AM
I'm not an AC tech but I sometimes play one on the internet....

Agreed that you probably shouldn't replace air duct just on a hunch. Now, it is common that houses are not designed with proper airflow and duct sizing in mind. If you're hoping to eliminate hot or cold spots in your house the duct size, location and total volume all are very important factors to consider. I personally think this decision should be made completely independent of your choice to replace the unit itself. The only reason I'd consider doing this is if the contractor gave you a giant discount on labor. Re-fitting ducts is more work than replacing an AC system unless you magically have all the ducts in the conditioned space of your house ala an industrial loft. A good smell test, if a contractor is just trying to replace, and not re-design the ducts sizing and layout then I'd be suspicious. Ask to see evidence of damage to the ductwork or crawl around in your attic yourself. An 8 inch duct from 1980 is going to move the same amount of air as an 8 inch duct from 2020. Insulation is better on newer ducts but you can wrap the old ones in more insulation anyway...

Just to get a new AC you might need to replace your air handler depending on if they still make the A-coil / condenser coil in that size. A smaller coil will fit but you will lose efficiency because it's going to be hard to get a perfect air seal so 100% of the air in the air handler will get treated. If you need to size up you might make the tradeoff now where you're getting a good seal for the AC coil but your furnace coil / burners are now mis-sized.

Another reason to replace both is if your furnace is quite old, the tech might discount your labor to install both at the same time. So if you think there's a good chance of a burner failing in a year or two you might want to replace now. If you're using electric strip heat then I would absolutely look into a heat pump so you can save some money on winter bills. Or if you're hoping to be more eco-friendly. Gas heat is pretty inefficient from an energy perspective but gas is dirt cheap as a fuel right now.

Reasons to not replace, gas furnaces usually last longer than AC coils. Once, I worked on a system where the AC coil had been changed 3 times but the burner from 1970 was still going strong and only had mild signs of corrosion. The gas burner could have worked trouble free another 20 years.

If money is no object I would think about getting a multi-stage / variable AC so it can dehumidify during the summer months. I find that 78 is pretty comfy if the humidity is in check but if your house is sitting at 85% humidity then 78 is WAY too sticky for me. All AC units dehumidify but ones specifically designed for dehumidification can do so more efficiently by pulling water out of the air but not working so hard as to drop the air temperature significantly.
Title: Re: Getting the AC and HVAC replaced
Post by: Sibley on June 05, 2020, 10:10:51 AM
I also have an older furnace and AC unit. While mine are both still fine, they will likely approach end of life at some point. Given the logistics of where all this stuff is, to me it would make more sense to replace both at the same time (and clean up that corner of the utility room, it's disgusting). To replace the furnace, they'd have to mess with stuff for the AC. To replace the AC, they'd have to mess with the stuff for the furnace. Even if they don't technically interact (no clue), in my situation they do functionally interact. I did have the blower motor (? the fan that moves the air) replaced last summer when it died, otherwise all is good.

This may not necessarily be the case for you.
Title: Re: Getting the AC and HVAC replaced
Post by: Fishindude on June 05, 2020, 11:25:02 AM
If your HVAC equipment is +/- 20 years old and it's been giving you some problems, I would most certainly do complete replacement which includes; the AC condenser, the AC coil in plenum, the furnace / air handler unit, as well as update to modern thermostats.    If the original ductwork was a quality installation, there is no need to replace any of it.   Should also be able to use the existing electrical feeds to equipment.

This modern stuff just doesn't last as long as it used to.   Too many lightweight aluminum and plastic parts, wiring and circuitry, and things are often installed in a less than desirable locations such as a dirty, damp basement, an attic, etc.    Back in the day, most places had a furnace only and they were much heavier metal with a standing pilot light and not much to go wrong, of course they were inefficient too.
Title: Re: Getting the AC and HVAC replaced
Post by: mizzourah2006 on June 08, 2020, 03:36:11 PM
Thanks for the comments all. I guess I wasn't very specific when I said full replacement, I wasn't sure what was meant by that when it was mentioned by others. It sounds like replacing the duct work is very uncommon and that's good to know for future reference.

 It ended up being the blower motor. He said it was fried and was pulling 16 amps and the most he'd ever seen one pull was 5 amps. I got it replaced. He said it's on its last legs, but it sounded like my options were to replace the blower motor or wait 2 weeks for a new install and it was already 81 in the house with a heat index outside of 101, lol. I asked how everything else looked after he replaced the blower motor and he said everything looked good. I'll probably let it go for the summer given I just sunk $700 on the blower motor and install. But I'll revisit the replacement next spring.
Title: Re: Getting the AC and HVAC replaced
Post by: Sibley on June 09, 2020, 09:50:33 AM
If it's old, but generally working well, you may want to just stick with it for now. New models don't last anywhere near as long. I don't expect a new furnace/ac installed today to still be in service in 20 years for example.

Same reason why I have a 30 year old dryer.
Title: Re: Getting the AC and HVAC replaced
Post by: alsoknownasDean on June 16, 2020, 08:07:39 PM
Yeah I had my old gas heater inspected recently, and it's unsafe. I'm getting three split system reverse cycle aircon units installed soon.

A newer system is likely more energy efficient. It would have been cheaper for me to simply replace the old gas heater, but that only heated the loungeroom and the new splits are likely more efficient.

The old air-conditioner in the lounge from 1998 will be going as well.

I'd just go with the 'recommended' size for the place.
Title: Re: Getting the AC and HVAC replaced
Post by: seemsright on June 16, 2020, 08:17:12 PM
When we had to replace our furnace. Our DD was a baby and it was Feb. I called the big local place and told them I have 3K that I could write them a check and what could they put in. In less than 2 hours I had a 3K furnace being installed. It turned out that with the tax write off my costs were stupid low.

It is worth working with companies because sometimes they just want to unload something that has been in stock that could work for your space. I am never picky.