Building a custom home - HVAC options - could use a bit of help please!

[milkman636]

There’s nothing wrong with using two central systems for this build. It’s a well proven approach with common systems that can be readily serviced by many different contractors. I do have a word of caution about using a single central return for each system. The area near each central return will be noisy because all the air for that unit will have to go through the one grill. Plus, air circulation will suffer in bedrooms and any other rooms that may have their door closed for extended periods of time.

Another potential benefit of a central system with dedicated returns is the ability to get isolation for quarantines. Some of the available
electrostatic air cleaners are capable of killing airborne virus particles, and having dedicated returns in bedrooms and living areas will do a better job of containing exhaled aerosol particles and taking them back through the filter before they can spill out to other areas of the home. It’s crazy that we have to think like this in these times, but I wish I had a central system for exactly these reasons. My house uses hydronic heat and mini splits for cooling. I miss the better air filtering that I had in my previous home.

Proper air sealing and insulation are really important areas to focus on for heating and cooling performance and cost. Some times you can spend a ton on technology that is supposed to be more efficient, only to have it underperform because other more important details were overlooked.

 

[bitseeker]

Heat pump ductless mini-splits.

 

[nickfank]

I did a similar installation 6 year ago, and just pulled out the calculator & did the math on energy consumption. It became obvious that the most energy-efficient units were the best deal, even if I had to borrow the money to deal with the initial cost.

It is true that the local climate is a factor, but generally speaking you're either heating more up north or cooling more down south, so the heat pump side doesn't change much. On the auxiliary heating side, I think you'll find that the high efficiency units really aren't significantly more expensive.

In NC, my guess is that the heat pump will be your most efficient heat source most of the time, since you don't get extreme cold. That being the case, it's worth noting that your location also lends itself to solar energy production, so having a heat source you can run off of electricity could get really cheap if you also install solar. (I ran the numbers and found that here in SW Ohio, solar paid for itself in about 9 years, and again, borrowing the money at current rates, I'd still come out ahead financially if I installed panels on our entire barn roof.)

Finally, I also found that the higher efficiency equipment tended to also get better reviews for longevity.

 

[nickfank]

Sorry-forgot to address the two-stage vs single stage question. two stage is indeed more efficient, and pays for itself quickly enough to justify the up-front cost.

A word of caution... An embarrassing number of installers will put in a two-stage system without wiring it to take advantage of the option. My installer did that, and I didn't notice he had cheated me until I replaced a faulty thermostat two years later and spent 30 minutes trying to figure out why there weren't enough wires going to it. When I sought the advice of a reputable HVAC tech, he told me he saw that about half the time.

 

[AnotherBueller]

I'd like to add to what Milkman 636 said. About 4 years ago we put in new HVAC systems in the house (Carrier) and when I brought up installing electro static air cleaners the dealer (Crystal City Heating) asked me why? He told me about a UV air purification option that kills viruses and sold for about half the price.
We've been very happy with that advice, it even removes cooking odors.
Per the dealer the life span of the UV bulb is about 10 yrs.

 

[3Ts]

We have a mini-split heat pump in our MIL cabin and it works quite well, except there is no real air filtering. We run a separate air filter with a carbon & hepa filter in it.

 

[Torvy]

Sorry-forgot to address the two-stage vs single stage question. two stage is indeed more efficient, and pays for itself quickly enough to justify the up-front cost.

A word of caution... An embarrassing number of installers will put in a two-stage system without wiring it to take advantage of the option. My installer did that, and I didn't notice he had cheated me until I replaced a faulty thermostat two years later and spent 30 minutes trying to figure out why there weren't enough wires going to it. When I sought the advice of a reputable HVAC tech, he told me he saw that about half the time.

No! Not two-stage. You want the variable speed. Think of it like the difference in speed control between a tractor with 2 speeds and a 4 range HST with infinite range.

Definitely need to make sure it is installed correctly, but get the best system, it pays for itself.

 

[milkman636]

No! Not two-stage. You want the variable speed. Think of it like the difference in speed control between a tractor with 2 speeds and a 4 range HST with infinite range.

Definitely need to make sure it is installed correctly, but get the best system, it pays for itself.

Two-stage is better than single stage. But, they do require two-stage thermostats to actually function as a true two-stage system. If a single stage thermostat is used the units will automatically go to the higher stage after a predetermined amount of time during an on-cycle. Two-stage thermostats will allow the units to cycle as long as they need to at the lower stage, as long as the room temperatures are not drifting farther away from the setpoint. I have had good experiences with both 2-stage heating and cooling. A good installation will require that the installer takes the time to setup the correct fan speeds for both stages to achieve appropriate temperature differentials between return and supply air. Pushing for fully modulating units will increase both the initial costs and future repair costs.

 

[tractortroof]

I have an opinion about geothermal HVAC systems that may not be popular, but it is based on owning 2 homes over the years with geothermal heating and cooling. My experiences are both with open-loop geothermal, so maybe folks with a closed loop system have had different experiences...

I don't see myself having a 3rd home with geothermal HVAC. Although it is absolutely true that geothermal is, by far, the most economical way to heat or cool a house from an operations perspective, there are downsides to geothermal that folks generally never mention.

1) The up-front cost is very high. Even with Federal and State tax incentives, geothermal is still expensive. Best case is that the tax incentives bring the installed cost into the same realm as a conventional heating/cooling system. And remember, these are TAX incentives -- typically, you still have to pony up the cash upfront and then get it back later through reduced Federal and State income taxes.

2) While this is true for all kinds of HVAC, you really REALLY need to make sure that the company you are using understands how to install geothermal properly. These are very sophisticated systems and a mistake in installation can cause you a lot of pain and suffering, and they can take a long time to identify and correct.

3) Geothermal systems require far less maintenance than traditional HVAC systems, but they do require some maintenance and occasionally repair. Not every HVAC company is well-versed in the ins-and-outs of geothermal. This reduces your options in the event that you have a falling out with the installing company, or in the event that company goes out of business, or if you need an emergency service in the middle of the winter. It does force the homeowner into being something of an expert in geothermal systems so that you can make an emergency repair on your own, or do some regular maintenance to save a few bucks.

4) Any very high efficiency equipment is going to be sophisticated. This almost always means that cost of replacement parts may shock you. As an example, I have a Florida Heat Pump split unit. The fan motor failed in the air handler. The cost of the new fan motor was $1600. I thought I was being lied to, so I called a number of other HVAC outfits. Two of them did not work on geothermal units (see my point above), but they told me that I was being robbed because a new fan motor was about $800 installed. A third outfit that did work on geothermal regularly told me that since Bosch had bought Florida Heat Pump, the prices on parts had gone up some and that the variable speed fan motor in my air handler was indeed a $1600 part. That $1800 repair ($1600 parts, $200 labor) ate up a LOT of the energy savings that the geothermal unit had brought me over the years.

5) This applies to open-loop geothermal, and likely isn't an issue for closed loop systems. The first home I owned with geothermal HVAC used a single well for supply, return and domestic water. It took the better part of a full winter to identify the proper height at which to hang the pump such that I would not suffer thermal mixing or freezing of the return water. This was a painful experience. My current home has a dedicated return well. This has eliminated that issue, but there are others. Water quality becomes a huge concern with open-loop geothermal. When my current supply well suddenly began producing large amounts of particulate matter at year 5 of geothermal use, I found myself struggling to find a proper filtration solution that wouldn't have me cleaning the filter daily. One must also have a properly sized and installed water pumping solution. I ultimately went with a constant pressure pump and a small pressure tank to limit the number of starts and stops that the pump would otherwise encounter when supplying a geothermal heat pump.

Anyway, these are just a few of the less-positive aspects of geothermal heat pump ownership. There is a lot to be said for a conventional HVAC system...

Every variable speed fan motor OEM costs $1600 to the consumer. We replace them with PSC motors for $800, seems like a bargain.

 

[tractortroof]

Please don't say that loud enough for my systems to hear you. ;-) I think they were about 3 or 4 years old when we bought the house, had it cut in 3 pieces and moved about 25 miles to a new location (paid someone with freon tools/experience to pump them down & reconnect/recharge at the new location). That was in 1997. It would be nice to upgrade to a higher SEER rating, but they just won't die; or at least won't die dead enough that I can't fix them. I've replaced the control boards in both furnace/air handlers (within the last 5 years or so), an air pressure sensor in one air handler (not sure that one wasn't the control board), and a capacitor, the fan, and the crankcase heater in one compressor. These failures were scattered across more than a decade, and I did all the troubleshooting and repairs, with a bit of help from the interwebs. If I'd been paying an HVAC contractor, I suppose I might have been more motivated to install new hardware by now, but as long as the rare and random repair costs stay well under $100, it's difficult to spring for new systems.

The coils started going south in the early 2000s, innovation donchaknow