Author Topic: Time to replace the HVAC  (Read 1166 times)

geekette

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Time to replace the HVAC
« on: February 17, 2018, 07:38:05 PM »
We have a 2000sf 2 level house in the hot, humid south.  Lots of windows too (although they're good windows and face mostly NW).

The old 3 ton gas pack (gas heat and AC in one unit) is 15 years old, and needs a bit of a recharge yearly, and it's the old expensive stuff.  The ductwork is 30 (original to the house).

The heat's fine, but I'm dreading summer, when we keep the thermostat on 78, but the bedroom gets over 80 (and more humid, what with 2 people and the adjacent bath).  The AC often doesn't run at night because the downstairs is cool enough.  We do run the circulating fan overnight, which helps a bit, and the ceiling fan, which helps a lot, but really, we need to change something.

We have a couple companies coming out in the next few days to price replacing the gas pack, the ducts, and see if we can dual zone the place.

Any suggestions for what we should ask?  Ductless mini-splits sound great, but I don't think they're done here (and I'd rather not be a guinea pig).

Exflyboy

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Re: Time to replace the HVAC
« Reply #1 on: February 17, 2018, 07:59:43 PM »
Ductless mini splits are great except you already have the ductwork installed yes? Unless you intend to rip out the ducts then I'd simply replace the AC system you have (presumably an outside aircooled condensor with a evaporator coil at the discharge of the furnace?).

You could possibly dual zone the existing ductwork with a motorised damper, and then you would have a dual stage furnace (or even a variable output furnace. Your old gas furnace is likely to be about 85%AFUE (85% efficient). You want a modern condensing furnace which will be about 96% AFUE. This will required a drain to collect the condensation from the furnace and run it to a drain, or outside to the landscaping if your local codes allow this.

Another option is instead of a straight electric powered AC system you use a heat pump.. This system will provide both heat and cooling via electricity, but the heat is normally cheaper than burning gas.. The furnace can then burn less (or no) gas to provide the required heat.

Another (more expensive) option is to use a geothermal loops. This will give you "free ish" heat in the Winter without burning gas. To be honest though, gas is so cheap these days its hard to justify this system.

The local contractors will know what works best in your area because heat pumps rely on the temperature outside for effective heating and cooling.

That should give you some options to talk about.

GuitarBrian

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Re: Time to replace the HVAC
« Reply #2 on: February 17, 2018, 09:46:25 PM »
R-22 is actually getting cheaper. About $15 a pound.
See,
https://m.ebay.com/itm/USA-FREON-R22-NEW-VIRGIN-REFRIGERANT-30LB-NET-SAME-DAY-SHIPPING/112817305740

You are legally allowed to buy it, and have a tech install it. I have several units that I am keeping running. A single 30lb tank has lasted 5 years. Some springs we add 3 or 4 lbs. Obviously check the valves •very• carefully. In my experience that is where leaks tend to develope.

If you decide to replace the unit, I have had great experiences buying my own equipment. Example a Goodman 3 ton gas pack.
https://m.ebay.com/itm/3-Ton-14-Seer-40K-BTU-Gas-Elec-Package-Unit-GPG1436040M41-GasPack-888-919-9119/142621328356

For 2k... Better yet, sign up for eBay bucks, get it on a 8% off day, and earn $100 for a future purchase. Once it arrives, make sure to follow the signing and damage instructions. Hire a tech at an hourly rate, and have him install the unit. You are on your own if you need service of course, but, in paying more for a system, you are basically pre paying for service calls... So you win if the unit lasts past the standard labor warranty period.

If the unit isn't precharged, I didn't look... order a can of 410a for ~$150 on Amazon.

geekette

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Re: Time to replace the HVAC
« Reply #3 on: February 23, 2018, 04:54:08 PM »
As tempting as the price is, there's no way we're going the DIY route, so I've gotten a couple quotes.  Both guys think the ductwork is fine (surprise).  DH would really like a steam humidifier because his skin and asthma get worse in the winter, and the pad humidifier that was installed 15 years ago is falling apart and doesn't keep up anyway, so he deals with portable units on each floor which are a pain. It seems like overkill for our area (central NC), but HWMBO wants it.

The cheaper guy quoted just zoning, a couple thermostats, and adding a steam humidifier (poorly reviewed Honeywell True Steam), hoping the old gaspack lasts a while longer ($4200). 

The other guy quoted a range up to $10k, with several options for HVAC replacement including single and dual stage up to 17 SEER and 95% AFUE, zoning, thermostats, and a better reviewed steam humidifier (Aprilaire 800).   

So gaspacks have a max AFUE of 80%.  To get more efficient heat, we'd have to install a split system, with the heat in the crawl space and the A/C unit outside.  The difference in price between the gaspack and the high efficiency split system is < $500.  However, it wouldn't be a good idea to just zone now and wait for the gaspack to die if we want the split system because stuff already done would have to be redone.

Do high efficiency gas furnaces blow uncomfortably cooler air?  Is a two stage system all it's cracked up to be?  We do plan on staying here for the foreseeable future, so paying more for efficiency and comfort is okay, but not if it's really no better.

Exflyboy

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Re: Time to replace the HVAC
« Reply #4 on: February 23, 2018, 05:06:29 PM »
No a high efficiency gas furnace does not blow uncomfortably cooler air.

Two stage is nice but unless you are shutting off half the ductwork say (if you wanted to shutdown the upstairs say), and providing the fan is matched to the ductwork then a single stage furnace is just fine.

When you shut off half the ductwork then most of that extra air volume would get blown thru less ductwork which will make it noisier if you used a single stage furnace.

I am about to replace my oversized furnace and will be installing a single stage furnace. This has been the standard for decades and works great.

robartsd

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Re: Time to replace the HVAC
« Reply #5 on: February 23, 2018, 05:16:09 PM »
Do high efficiency gas furnaces blow uncomfortably cooler air?
No. The temperature of the conditioned air coming out of the furnace would be basically the same as less efficient furnaces. The efficiency gains come from extracting more heat from the exhaust air before sending it out the flue (using the heat to preheat the incoming air) and using outside air for combustion intake.