Is the Lochinvar Noble any good?.

[Arlen Angell]

I’m building a 30x48 cottage on my farm for my mother to live out her golden years in. It will be a Morton building so slab on grade. I’m in Southeastern Minnesota. I’m starting to put together the HVAC plan, and it will have in floor heat, but I will probably have a water coil too for a little forced air heat. She won’t need allot of domestic hot water, and I would guess the building heat requirements would be around 50k BTU max.
There are allot of tankless boiler/water heater combos out there.
I’m in the HVAC controls business and Lochinvar is definitely a brand that I’m familiar working with.
Would the Noble be a good choice?

 

[Dana]

Low mass combi boilers are usually a good fit for houses with high heat loads and moderate domestic hot water needs.

With a properly aggressive Manual-J the real heat load of a ~1500' IRC 2018 code minimum house that isn't over-ventilated would have a design heat load of about 25,000 BTU/hr @ -10F outside, +70F inside (not 50K), and even during Polar Vortex disturbance event lows in a high wind it might reach 35K.

The smallest of the line NKC110N would have a reasonable minimum modulation range of about 10K out for a 25K design load, the domestic hot water output would be painfully limited for filling a bathtub in winter. Even the mid-sized NKC150N would have a minimum fire rate of half the design heat load or more. The largest of the line NKC199N would have reasonable hot water performance, but it's min-fire output isn't much lower than the heat load at -10F. While the thermal mass of slab heat would limit the short-cycling potential it's less than ideal.

So could you make it work? Sure. But a condensing tank type water heater with a ~75K burner would easily cover both loads, and would fill bathtubs twice as fast in winter as the biggest Noble.

If the slab can't emit the full load hydro-air coils can make up the difference. Thin-profile floor mounted hydro coil units can even micro-zone it, and usually a better way to go than ducted solutions in an otherwise slab heated slab on grade house.

 

[Sponsor]

 

[Arlen Angell]

Low mass combi boilers are usually a good fit for houses with high heat loads and moderate domestic hot water needs.

With a properly aggressive Manual-J the real heat load of a ~1500' IRC 2018 code minimum house that isn't over-ventilated would have a design heat load of about 25,000 BTU/hr @ -10F outside, +70F inside (not 50K), and even during Polar Vortex disturbance event lows in a high wind it might reach 35K.

The smallest of the line NKC110N would have a reasonable minimum modulation range of about 10K out for a 25K design load, the domestic hot water output would be painfully limited for filling a bathtub in winter. Even the mid-sized NKC150N would have a minimum fire rate of half the design heat load or more. The largest of the line NKC199N would have reasonable hot water performance, but it's min-fire output isn't much lower than the heat load at -10F. While the thermal mass of slab heat would limit the short-cycling potential it's less than ideal.

So could you make it work? Sure. But a condensing tank type water heater with a ~75K burner would easily cover both loads, and would fill bathtubs twice as fast in winter as the biggest Noble.

If the slab can't emit the full load hydro-air coils can make up the difference. Thin-profile floor mounted hydro coil units can even micro-zone it, and usually a better way to go than ducted solutions in an otherwise slab heated slab on grade house.

The only reason I was thinking of an air coil was I need the duct for cooling anyway.

 

[Dana]

Have you considered cold climate mini-split heat pumps? Both Mitsubishi & Fujitsu have units fully characterized for output at -13F, and can be sized to support the entire heat load if need be. Sized for the cooling load they would likely still need the hydronic floor at design temp. You're probably looking at 1- 1.25 tons of cooling load (unless designed badly.) A 1.25 ton Fujitsu 15RLS3H will deliver about 14-15,000 BTU/hr @ -15F, as will the 1.5 ton Mitsubishi FH18NA.

Fujitsu makes a nice 1.5 ton ducted mini-split that's only fully specified for heating down to -5F (where it delivers over 18,000 BTU/hr) but uses the same vapor injection scroll compressor technology that gives their fully cold climate mini-splits the higher efficiency and extended cold temperature capacity. The primary difference between it's outdoor unit and the cold climate wall-coil types is the absence of a pan heater to keep defrost ice from building up when used extensively during the winter. Despite the absence of a pan heater there are folks in Minnesota in using them as primary heat in very high performance PassiveHouse US certified houses. Keeping the drain from plugging with ice is the most important aspect, and it's possible to rig up your own ~100-150watt pan heater and just plug it in to run continuously for the weeks when the daily highs won't be hitting the freezing mark. Another nice aspect of that series ducted mini-spit is that (unlike their competition) it can be mounted vertically in a micro-closet for easy access for maintenance and filter swaps, taking up less than 10 square feet of floor space. It's a lot smaller than a 1.5-2 ton FirstCo or similar hydro-air handler. The air handler is rated for up to 0.4" w.c. (half that of a full sized air handler), but that's not a hard design constraint to manage with for a 1500' house.

Ducts in an attic above the insulation will create cold drafts cascading out of the cool registers when it's cold out unless they are actively heating, and adds to the raw heat load (and the cooling load). With a ducted solution putting the ducts & air handler in soffit below the ceiling level, fully inside the pressure & insulation boundary of the house fixes those issues.

 

[Arlen Angell]

I will give that some thought. I didn't realize that those mini splits are able to heat down in those temperatures.
I should be able to keep the duct work below the insulation. The sidwalls of the building will be 10 feet, and I plan to drop down the bedroom and bathroom to 8 feet. I'm hoping to conceal the ductwork in that space.
Is the 10-1 turndown on the Noble about as good as it gets, or are there others that have a higher turndown? I know 10-1 is pretty darn good, just curious if there a better ones.

 

[Dana]

Yes, 10:1 is about as good as it gets with combi boilers or even simpler mod-con boilers at the smaller sizes. The fire-tube heat exchanger versions such as the Noble NKC199N or HTP's EFTC-199W are more forgiving on the heating system design side than water tube heat exchanger types such as Navien's NCB series, but the NCB-180E or -210E might be a better fit for your actual load, not that any of them are a great fit.

 

[WorthFlorida]

Please consider a separate zone, unless it is already in the plans, for the bathroom from the main heating plant to warm the floor in warmer weather where the whole home will not need heating. If not, an imbedded electric heating grid under the bathroom floor tile will do. It will allow to warm the bathroom, or at least the floor for the times where its too warm for the central heat to be running but cool enough where mom may feel chilly.

As moms and dads age things sure change. My father lasted to 90 but his health changed and in the last few years he was cold all the time, even when the room was 85 degrees and had a flannel shirt on. He kept an oil filled electric heater under the kitchen table and it was on most of the time, all year. My mom in the last 2-3 years of her life needed 24/7 care and the full time care takers would occasionally have to strip her down and wash her while she stood up. A chill to an aged person can be deadly.

 

[Dana]

As if on cue, an article in today's Midwest Energy News touches on the use-case for cold climate heat pumps for air conditioning & auxiliary heating.

If used for primary heating it's better to go with Fujitsu than Mitsubishi, since the latter will turn themselves off at some point when it's in the -20sF outside (it could happen as warm as -18F according to the spec), and will automatically re-start when it warms up to -13F. The Fujitsu units don't do that, and continue to operate and put out heat at -30F, albeit at an unspecified capacity & efficiency. (I've heard have second-hand of a house being heated comfortably at -32F outdoors from a guy in Quebec who heats his place with four 3/4 ton Fujistus.)

There are a few ductless and ductless mini-splits fully specified at -22F, but the local distribution & support for them in North America is pretty limited. The Chinese vendor Gree (the largest manufacturer of air conditioning equipment in that country) is distributed by some of the box stores with a few models rated at -22F, but the support chain isn't as good as Mitsubishi/Fujitsu/LG. The 1.5 ton Gree Crown 18HP230V1A is good for about 15KBTU/hr @ -22F, and probably covers the cooling load.

Midea/Toshiba has a few rated that low as well. A decade ago Midea began partnering with Carrier (I believe all Carrier mini splits are really relabeled Midea units) , but Carrier isn't selling any of the -22F versions in the US yet. Midea is a large Chinese multi-national doing all sorts of home appliances, that has been developing product with Toshiba for their Midea-branded AC refrigeration & heat pump technology for a couple of decades now. They effectively own most of Toshiba's refrigeration compressor manufacturing capacity, which is top-shelf stuff built in China. If there were more of a support network I'd be inclined to dig in further, but in my area Mitsubishi & Fujitsu together own something like 80% of the market for cold climate heat pumps. I've yet to find a local Midea installer, and my local Carrier installers seem pretty clueless about cold climate heat pumps. Like the other cold climate heat pump vendors, in heating mode their "Premier Hyper" units are good for at least 100% of their rated cooling output BTUs in heating mode at +5F or colder, but also specify a capacity & efficiency at -22F in their capacity charts (not available online). They look good on paper and are very cost-competitive but without a support network I'd be reluctant. YMMV.

 

[Arlen Angell]

I might just go with a small air handler, water coil to trim the slab heat and a small condensing unit for cooling.
I still like the idea of a medium (or small 100k BTUish ) sized tankless combi. 2.5-3 gpm would do her I hoping for domestic hot water.
She doesn’t want a bathtub, so could a person get away with 2-3 gpm?

 

[Dana]

A 100K-ish combi isn't going to cut it at MN type incoming water temperatures. The NCK110 is good for 102,000 BTU/hr. A 40F incoming water temps and 105F at the shower head is a 65F delta-T, so even the theoretical max flow would be 102,000/65F= 1569 lbs/hr or 26lbs/minute, which is (/8.34=) 3.1 gpm. With line losses etc the reality is likely to be just shy of 3gpm.

That's ONE shower with no other simultaneous draws. (Even a low-flow shower is 2-2.5gpm.) She would have to schedule her bathing to not conflict with laundry / dishwasher use, or visitors washing their hands, etc.

The NKC150 would be good for about 4 gpm, which might be OK, but really the NKC199 at about 5.4 gpm (at a 65F rise) would have enough margin to be able to shower without concern for what the appliances or visitors might be drawing.

Condensing tank type water heaters work just fine with radiant floors & hydro air without any flow constraints. Isolating the heating loop from the potable side with a plate type heat exchanger is highly recommended to limit the legionella potential and other stagnation concerns, but it's not rocket science to design. HTP's all stainless Phoenix Light Duty with the 76K modulating condensing burner with a ~3:1 turn down ratio is pretty commonly used this way as a combi. (It only "Light Duty" in terms of commercial water heater burner sizing.) An endless shower while the heating zones were operating could deplete the tank down to less than showering temps, but it can keep up with a 2 gpm shower forever when the heating system isn't running. The 50 gallon version runs a bit more than 2 grand through distributors, often less direct from HTP. Westinghouse re-labels it and sells it through box stores for a few hundred less. The HTP model number is PH076-50, the Westinghouse number is WGR050NG076. It is EXACTLY the same unit- when you call Westinghouse tech support the phone rings at HTP headquarters. The warranty and sales support chain is different.

As long as you don't oversize the hydro-air coil relative to the heating load a 76K burner is plenty. A 1.5 tonner like the FirstCo 18HBXBX-HW or similar is probably about right- run a real Manual-J on the cooling load. In heating mode running it a low cfm (= low wind chill) and low gpm can throttle back the output to where it's just supplementing rather than taking over the floor heat.

The basic system schematic for that approach looks like this: