New construction & HVAC choices/opinions, zone 5/6

NuMexJoe

New here, and pleased to find a sharing, knowledgeable community. Forgive me if this is not the place for my question, please. The wife and I are building our retirement house and need to make some decisions on HVAC. It’ll be an 1,800 sq ft residence and we’ll rarely use the guest bed & bath upstairs. Mostly open floor plan on the main floor except for the master bed/bath. It’s not uncommon to see single-digit lows this time of year, but the norm is more like 20*F for a low and 45-50*F for a high in winter. There are ~3 weeks in the summer when you’d want A/C. Depending upon which map I consult, it looks like we're either zone 5b or 6, with mostly clear, sunny days.

We’re going to have a 42k btu gas log fireplace (I’m done with wood and pellets), but since it’s only 63% efficient, we need something else for our primary heat, and we’re also done with radiant baseboards. I was looking hard at a multi-zone ductless mini-split heat pump, what with the new refrigerants that make them useful in much lower temperatures, but it’s hard to find anyone with good things to say about the reliability and longevity, and you’re blowing air that doesn’t feel especially warm. Geothermal is theoretically possible, but we’d like to avoid ductwork, so it’d just be a different heat source for the ductless mini-split heat pump with the same reliability questions. Our builder and his plumber both advocate for radiant in-floor hot water that would be stapled up and insulated underneath, fed by an efficient gas-fired on-demand “boiler”. We’re not ones to keep futzing with the t-stat, so that might be a good fit, and it’s quiet. If we go radiant in-floor, we'd do a couple ductless minisplit heads for A/C.

It'll be a tight, well-insulated house, so I don’t need to have the absolute most efficient system. I just want one that's quiet and reliable. It’s a small town with no Trane or Carrier presence; everything has to come from the big city 2+ hours away. It seems there's a wealth of experience here, so if you were starting from scratch, what would you choose and why? And thanks!

Jamie Hall

If you ask ten of us, you'll get at least twelve different answers...

First thing I'd do would be to work with the design (architecture) and siting of the hosue. You want to have as much insulation as is reasonable, but you also want to be able to have some air exchange, for indoor air quality control. Then arrange your glazing so as to get as much benefit from winter sun as possible -- in your zone, if you used a high mass (concrete slab) first floor, you could get almost 100% solar heat that way without any funny tricks or collectors or what have you.

Depending on how well you manage the solar gain part, your remaining heat load will be quite small and could be managed quite easily with a mini-split heat pump. This would give you air conditioning when wanted, and heat in the winter -- with the gas fireplace being used to give you a real feeling of warmth.

Otherwise, if a high mass floor is not an option -- and it may not be -- I like the idea of a radiant floor such as you have mentioned. Your heat load should be well within the capability of such a floor. In fact, the biggest problem will be a boiler to power it. I do NOT like the idea of using an on-demand type water heater for such applications. They are not built for it, and not intended for it. A much better option would be a "combi" (you'll probably need the smallest you can find!) or a separate boiler of the modern mod/con variety, with outdoor reset. You could have a separate on-demand gas water heater for your domestic hot water.

WMno57

You mentioned three things that jump out to me as items your decision should be based on.

• Retirement
  
• Clear sunny days (this usually means cold nights, New Mexico?)
  
• Small town
  

Is this location at altitude? Only three weeks of AC in summer?

WMno57

also, Slab, Crawl Space, or Basement?

Hot_water_fan

I'd recommend you keep it simple: ducted with a heat pump, with an optional furnace for emergencies. Ducted is the route most Americans take, so you'll have people to service it. You can then determine the level of comfort you want - I have a variable speed unit that's silent and comfortable, but a single speed blower is another option. With a low heat loss, your ducts will be small.

KC_Jones

You really need to have a Manual J heatloss calculation done for that house to get an idea of what you need, I'll explain why with some shoot from the hip information.

"1,800 sq ft"
"It'll be a tight, well insulated house,..."
"We’re going to have a 42k btu gas log fireplace"

Shooting from the hip with those three pieces of information I'd say your heat loss will less than 30k btu's. That heat source most likely has enough heat output to heat that home by itself. So, if you put in a system that will actually heat the home, any system, then that gas log is going to cook you when you turn it on because it will effectively double the heat you need, and that's on the coldest day of the year, on an average day it will be massively oversized. If you like the romance of the fireplace, then by all means put it in, but you will want to turn the primary heat source down or off, in advance before you have your romance and be prepared to walk around in summer outfits when you do turn it on. I'm really not kidding here, you will be shocked by what it will do, especially with a properly built tight house as you describe.

Given your description I'd either go with radiant, well because it's the king of comfort IMHO. Or I would do a full ducted system. I can't advocate for mini splits for AC as you describe because honestly it makes zero sense to me on new construction. A proper ducted system is going to be much more comfortable when compared to mini splits. I mean you are building ground up, you should absolutely have a properly designed, fully ducted system installed at least for the AC side, but honestly just do a heat pump and be done with it. Considering the temperature range you say is common the heat pump seems like a good fit, most likely don't even need the heat strips which kill the efficiency, as long as the components are properly sized.

In addition, with a properly tight house you will need the duct work for an ERV system to make sure you are getting proper fresh air into the home. So, for me, you will need some duct work no matter what, so why not have a fully integrated duct system?

"but we’d like to avoid ductwork" What about a ducted system do you have an aversion to?

I will emphasize that any system will need to be designed properly, and that starts with a Manual J heat loss, any contractor that tells you different should be immediately dismissed an not considered.

This statement is a bit concerning: "fed by an efficient gas-fired on-demand “boiler”." On demand is a water heater not a boiler, a boiler is just that a boiler for space heating, using both in on sentence is someone's misunderstanding, hopefully yours and not the contractors. Perhaps some clarity is in order there. You absolutely do not want to use an on demand water heater for space heating, it's a misapplication of the product.

With what I've said and the other responses one message you should get is you need a lot less heat than I think you realize. This is a common misunderstanding with most people. Do this small home correctly and you could heat it with some candles, or as Jamie said, possibly all passive solar. You'd be amazed how well that can work.

WMno57

Hot_water_fan said:

ducted with a heat pump, with an optional furnace for emergencies.

Why not ditch the heat pump and just go gas forced air furnace for winter, and central AC for summer? @Hot_water_fan, is your recommendation based on your environmental leanings, or the customer's best interests?

Hot_water_fan

Why not ditch the heat pump and just go gas forced air furnace for winter, and central AC for summer? @Hot_water_fan, is your recommendation based on your environmental leanings, or the customer's best interests?

First, as @KC_Jones pointed out, the heat loss could turn out to be pretty low - likely well under the capacity of a furnace. Heat pumps come in smaller sizes, and will provide increased comfort than an oversized furnace can - yes, even those than can modulate some. 

Second, the cost delta between an AC and a heat pump is extremely low, so why not provide additional heating fuel options? You could have a gas furnace, plus the ability to use electricity for heat, which lets you pick between gas, coal, nuclear, wind, solar, hydro, etc. Provides the customer with more options, the American way. We get questions everyday about propane vs. heating oil, people like options. 

Sal Santamaura

NuMexJoe said:

...There are ~3 weeks in the summer when you’d want A/C...

That will increase going forward. How much longer it gets depends on how long your retirement lasts. Another factor to think about while considering the HVAC options experts offer in this thread.

NuMexJoe

WMno57 said:

also, Slab, Crawl Space, or Basement?

Yep, 7300' altitude, and the design thus far is crawl space rather than slab.

psb75

If house is tight and energy efficient, you'd best ALSO consider HRV or ERV equipment. Air change devices.

NuMexJoe

Well, this is why I asked. Some great info to digest - thanks! KC_Jones, the misunderstanding regarding the on-demand is mine. The boiler we looked at as an example installation was so much smaller than our current one that I incorrectly assumed it had no tank.
I'd not considered needing ducting for fresh air exchange, but that would argue for just going with a properly-sized heat pump. I was not a fan of the (only) one I had 30 years ago in Phoenix (noise and barely-warm air blowing on you in the winter), but I realize much has changed.
While passive solar wasn't a bid design consideration, we do have a bank of windows that face S-SW.
Yes, the fireplace is for ambiance (and it's nice to have a backup heat source up here in the mountains), and that was going to be a drawback of the infloor radiant, and you can't simply turn it off while the fireplace is in use.

WMno57

NuMexJoe said:

I don’t need to have the absolute most efficient system. I just want one that's quiet and reliable. It’s a small town

• Full basement
  
• Ductwork
  
• Gas forced air furnace in basement
  
• Central air
  

If the gas fireplace wasn't a requirement I might consider an all electric home (no gas bill).
If Radiant floors are a requirement I would recommend pex in slab, with the most reliable boiler (small town) you can get.
I don't like the crawl space. Too easy for pipes to freeze. You may be away in winter for an extended period (visiting family, hospital, short term rehabilitation, etc).
Your home should also be built with Ageing in Place features.

hot_rod

Radiant will be quiet, clean and comfortable, and the most expensive option. Radiant walls or ceilings are another option. A combi boiler would be a good match for your application.

For cooling and heat redundancy a ducted system allows heat, cooling, air filtration and ability to add humidity.

I visited the Homebuilders show this year. A heavy emphasis on products for the aging population, from elevators to grab rails, senior specific fixtures, low or no maintenance siding, decking, etc.

Outdoor kitchen equipment was popular also.

A couple favorites, a Jetsons like elevator instead of stair climbers. Multiple grab rails for a shower or tub.

EBEBRATT-Ed

Depends on your heat loss but I am leaning (surprise, surprise, because I am not a big heat pump fan) to #1 geothermal heat pump, but if cost is a factor #2mini splits. The gas fire place will give you a emergency back up to the geo or Mini splits if nothing else.

Check out WaterFurnace geo units I installed some years ago and was impressed by their quality..

If you only using the second floor intermittently a mini split up there (so you can keep it shut down or on a low setting) and geo downstairs (which would reduce your ductwork) would do the trick and would provide 3 sources of heat in an emergency which is important if your service tecs are hard to get slow to respond or 2 hrs away.

I would not go radiant hot water unless your are convinced you can get someone knowledgeable in your area to service it.

In fact getting some one who can install/ service whatever you decide to install is probably the 2d most important thing you need to help you decide. #1 is an accurate heat loss.

If the building is really tight I would include a HRV

Hot_water_fan

Geothermal is just in a tough spot right now: interest rates are up, heat losses are decreasing for new homes, and air source heat pumps are advancing. Saving money upfront usually overcomes slightly higher operating costs (which are not guaranteed - some geothermal heat pumps underperform air source).

NuMexJoe

Jamie Hall was right about 12 different answers! But I appreciate all the input. An all electric house is out of the question given the reliability of the US grid and our winter weather. And as EBEBRATT mentioned, making sure you've got someone to service the system is important. That's part of the reason for considering infloor radiant, as that's what our builder and his plumbing contractor install more than anything else. I checked into WaterFurnace, and the closest dealer is >100 miles away.
Are ductless, multi-head minisplit systems more reliable than I've been lead to believe? That would satisfy the need for A/C and a redundant, efficient heat source which could be supplemented by the gas fireplace.

WMno57

NuMexJoe said:

as EBEBRATT mentioned, making sure you've got someone to service the system is important. That's part of the reason for considering infloor radiant, as that's what our builder and his plumbing contractor install more than anything else.

Right. Who will service this in 2028? New Mexico is the land of forced air. I'm surprised to hear that any new homes in NM are being built with radiant. I would also guess that most buyers in NM are only familiar with forced air and you or your estate will have a hard time selling a radiant home.
Heating systems should be installed by heating contractors, not plumbers. Your builder is taking a shortcut by using the same guy for domestic hot water and heating. You will pay the price for this down the road. There must be a HVAC company that services your town. Talk to them.
I'll bet trades people who know and service hydronics are few and far between in NM.

hot_rod

What town are you near, there are some knowledgable radiant contractors in most of the larger towns, certainly the ones with $$ or near the mountains. Many of them travel for work.

You find them by asking at the wholesalers many small shops are underground, no need to advertise.

All mechanical devices can and will breakdown, just give them time.

Sal Santamaura

NuMexJoe said:

WMno57 said:

also, Slab, Crawl Space, or Basement?

Yep, 7300' altitude, and the design thus far is crawl space rather than slab.

What is the topography of your lot? There was a '70s/'80s article (Popular Science? Fine Homebuilding? Or?) that detailed a passive solar house in your area. It was sited on a flat spot atop a south facing slope. There was an area of glazing around 20 feet wide going down the slope something like 25 feet -- these are rough guesses from long-term memory of the illustrations. Beneath that glass were concrete channels feeding into a hypocaust heating system beneath the attached single-story house. Ever since I've wondered how that system performed over the long term. If you can find out, it's done well and your land is compatible, there would probably be no need for concern about who will maintain it. Other than perhaps cleaning the glass occasionally, of course.

EdTheHeaterMan

I like the radiant floor idea because my feet are always cold. Old folks sometimes get that with poor circulation.

The problem is getting someone local to install and ultimately do the repairs and maintenance on that stuff. You don't want to be stuck with no heat and no one local that knows how to fix it.

hot_rod

You have a circulator instead of a blower, not much difference for parts and troubleshooting for any motivated service person or mechanic