Workshop with dwelling above: Heating advice?
Hello,
I’m a 26 year old carpenter living in Zone 7A with 5040 degree-days and planning on building a workshop with dwelling above in the spring of 2018. The structure is 24’x36′, 2 stories, bottom floor 4″ slab and 2nd floor 1.5″ concrete topping. Walls are either 8″ SIPs or 2×6 with 2″ XPS on exterior, yet to decide. Also there is an attached 12’x36′ deck covering a carport on the west side. My hope is to have a +/- 7kW PV grid tie system on the property, and Natural Gas is available as well at the property line. My research has led me to down a few paths for heating this building, but first here is what is driving this decision:
– Price
– Ease of Installation
– Efficiency
Option A: NG Combi Boiler from Navien for hydronic heating in both slabs. I’ve almost written this off because of cost to install NG, tubing, manifolds, etc. As well as have another utility bill to pay.
Option B: Electric heating cable reel from Ouellet for each room. Install cost is about $4k and allows for individual room adjustment. And I can install myself. Doesn’t seem to be an overly popular option out there though.
Option C: Wall-mounted Mini-Split Heat Pump from Fujitsu. Cons include sub -25c temps in winter and install and initial unit costs. Pros include cooling for the few days a year it’d be nice to have and better efficiency.
Would love to hear peoples experiences and thoughts. Thanks in advance!
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Replies
User-6964558,
First of all, can you tell us your name?
Second: If you want to install continuous rigid foam on the exterior side of a 2x6 wall in Climate Zone 7, the minimum R-value of the foam layer is R-15, so 2 inches of XPS won't work. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.
Third, most green builders avoid the use of XPS, because XPS is manufactured with a blowing agent that has a high global warming potential. For more on this issue, see Choosing Rigid Foam.
Finally, I advise you to install a cold-climate ductless minisplit from Fujitsu. At an outdoor temperature of -25°C (-13°F), the Fujitsu minisplit will work just fine.
From personal experience in Maine, the Fujitsu minisplit will work well.
As for the workshop, will it be heated all the time or just occasionally? Might you want to treat the two levels separately, with robust insulation and air sealing in between?
If not doing radiant, why concrete on second floor?
Whatever you do for heat, put at least 4" of reclaimed foam under the bottom slab.
Thanks Stephen and Martin,
I'll have to take a closer look at cod reqs for minimum R-value, but I think you may be right, and have to stick with 3" min. Also, XPS is readily available here, semi flame retardent and gets better with colder temps (all important factors).
The workshop would be heated semi regularly, a few full days a week is my best guess at this point. I will try to keep the two floors as seperate as possible, as the bottom will be a woodwork shop I'd like to reduce dust and sound transfer. The 2nd floor concrete would be because of sound transfer but also polished concrete will be my finished floor preference.
If ductless minisplits for both floors end up cost 2x or 3x the amount, still worth the investment and a good ROI?
Thanks,
Nathan
XPS loses performance over a few decades as it's HFC blowing agents dissipate. The manufacturers won't warranty anything more than 90% of labeled performance, and even that is a stretch (figuring few if anybody is going to test it and try to collect after 40 years of service.) From a design perspective it's prudent to derate it to ~R4.2/inch (the fully depleted performance level, the same as EPS performance on day 1, and day 20,001.) It's not clear that it would test at better than R4.5/inch (the warranty performance) after a mere 15 years of service.
From a design point of view in zone 7 for your stackup it's legit to use the 40F ASTM C518 tested value for EPS, which for 1.5lbs density "Type-II" EPS would be ~R4.5/inch, but not the 25F value (~R4.7/inch) so you'd be good to go with 3.5" of EPS or XPS (fully-depleted). If cheaping out with Type-I (1 lb nominal density) EPS, even at 40F you're looking at 4". Here is a typical vendors' ratings chart at different temperatures & densities:
https://www.insulfoam.com/wp-content/uploads/2014/04/Insulfoam-EPS-Physical-Properties.pdf
For the code minimum exterior R for dew point control at the sheathing, see Table RR702.7.1:
https://up.codes/viewer/utah/irc-2015/chapter/7/wall-covering#R702.7.1
Tankless combi boiler solutions are usually a serious mis-match for buildings with low heat loads, particularly for insulated houses. The domestic hot water performance requires up-sizing the thing to the point where the min-fire output is more than half the design heat load. They're a better match for heat leaky houses with huge heat loads and moderate domestic hot water loads. If going for a combi, a tank type combi makes more sense.
Getting to the optimal solution starts with calculating the heat load at the 99th percentile temperature bin for your location. If you don't even know your wall stackup and U-factor it's too early to spec the heating solution. Window performance is also going to be critical to making those calculations too.
Getting to Net Zero with PV array that comes anywhere close to fitting on the house will require leveraging it with a heat pump, and Fujitsu has a decent track record in climates like yours.
Simulating the house with a tool such as BeOpt for both peak load and annual energy use would be useful too.
Would minisplits really cost 3 times?
IF you can self install, I would think not.
I know you didn't ask, but you have 100 sq ft of hallways, and I hate hallways
If you slid the bathroom to the right and made the hallway shared space with the kitchen, it makes the kitchen larger at no cost, and then moved the bathroom door to the kitchen or living room side eliminates the bedroom hallway almost entirely, and make room for the closets that you left out.......
Keith, I need to do some more calculations and speak with the local rep's but I had calculated that each floor with electric mats would cost about $2000 installed, whereas a Fujitsu Mini Split would be about $3500-4000 per unit.
Thanks for the floor plan advice, thats a really great idea. The designer I work with had told me she lined things up for easier stacking for the plumbing, but moving the whole bathroom 3.5' in line with the floor joists shouldn't make much of a difference, So I'll suggest the change. Also, not planning on installing closets at this point, would like to use furniture to keep things open.
And Dana, thanks for all that info I'll take a look into that more when Im deciding on my wall system. Just waiting to get exact pricing on SIPs and conventional stick framed with exterior rigid.
Thanks,
Nathan
If you are building a thousand ranch houses on spec, the plumbing install costs matter. While it is good not to be stupid with plumbing layout, it should never drive the floor plan. They must teach architects that in the beginning of some mandatory class before they fall asleep[just teasing guys, relax]
I cut over 8 feet of hallway out of my last house because the designer put the family bathroom at the end of the hall to combine plumbing with the master bath. That space became closet and master bedroom space. The bathroom was moved more central where guests would want it.Actual costs? Unknown,but it amounted to about 14 feet of hot water pipe, since the cold ran past the bath, and the drain also ran past it. I see similar costs to you, from nothing to a few feet of drain and water line.
Even with PV your savings on the mat will disappear quickly in operating costs.
Just cause I had nothing better to think about....
sliding the bath over allows you to get rid of most of the hallway and you get the same size bedrooms with the adjoining wall becoming a pair of closets. You need closets, if only to throw your junk when your parents/SO/potential SO/parole officer/loan officer comes to visit.
And since the bathroom is now over by the stairs, you can steal some space above the steps for a bathroom window, which is nice, and the additional ceiling space will make it feel bigger
Stack on the left side of the bath means there should not be any venting issues for the island sink. You don't have your laundry shown, and since I assume your floor joists run the 24 foot length, no drain issues, maybe you need a vent for the laundry, maybe.
And you are not really going to walk outside to go inside your shop right?
OK I'm done messing with you........
Hey Keith,
Thanks for the advice. I really want to utilize the area under the stairs, so I'll use that for my mechanical and laundry. Rough idea attached.
Also, I just threw in the older plans, have a look and think. Curious to hear your changes.
Remember, for me this is what drives the project: Budget, Efficiency, Aesthetic. The order may change from decision to decision :P
see att for space for bath window cubby
the only complexity to your plumbing is distance to vent stack. If the vent stack is in the wall between the bath and the kitchen, I think everything is within vent distance, where if the stack was over at the stairway, the kitchen sink might be too far away. Don't listen to me, check with a plumber, but don't let the plumber mess up your floor plan because he wants to save you 5 feet of pipe.
Nathan,
Can you live with virtually no windows in the workshop? Seems kind of extreme.
Keith, alright I'll look into the stacking a little bit closer. Also, still not convinced I need closets, bachelor living at it's finest!
Steve, there are windows in the O/H garage door. But no other windows. Because grade will be 4' above slab height on 3 sides, and with the amount of snow we get, I did think I could get windows in the shop that were above the snow level as well as within reaching distance to open and close in the summer when I need to get air flowing. My thought was to take the money that I wont spend in lower windows and spend it in the suite windows. And in the summertime open the OH door as much as possible.
Here is an updated revision on the plans. Note: the bathroom hasn't been moved over yet.
-Nathan
Nathan,
I had a similar garage door in my last house. Even though it had a southerly exposure, it did not let in a huge amount of light.
Another option for the garage might be a couple of light tubes. You could locate them over your work areas for maximum benefit. Velux (http://www.veluxusa.com/landing/light-tubes-tubular-skylights) has been making light tubes for a long time, but there may be other options that work just as well.
Nice looking building
Windows not right under the drip line can be pretty close to the ground with little negative impact. I would add one or two. Imagine being in the bathroom when the power goes out and trying to feel your way to the exit. Not being in a cave can help keep you working[I know, I work in a cave]
I can see from you new details that the plan is to have the stack probably lined up with the downstairs toilet, do yourself a favor and spend the hundreds of dollar it takes to make the plumbing slightly more complex.
my very crude explanation of what I am talking about:
Oh, and to get back on topic, you could put a ducted minisplit above the now tiny hallway between the bedrooms and dump a small duct to each and a larger longer duct above the bathroom to the living room
https://www.acwholesalers.com/Mitsubishi-Air-Conditioners/SZ-KD09NA-9000-BTU-15-SEER-Ducted-Heat-Pump/19626.ac?catId=cat1031&mainCat=&subCat=&trail=5188:Yes
It does not appear the ducted units come standard with the hyper heat allowing super low temp operation they are 'only' rated to -4F but I don't know the reason, perhaps one can buy the head and compressor in other combinations
Keith, I think Im pretty set on the original idea of a NG boiler and then also adding a wood fireplace to the suite above. I spoke with my local heat pump dealer and after explaining the project and costs I think Im set on the boiler hydronic route.
As far as the floor plan goes, I took your idea and modified it slightly so that I have a linen closet for storage and for a suite dedicated 100amp panel. I'm still not convinced on the shop windows, but if I can squeeze some wiggle room in there for it. Then that's what I'll do. Here it is below