Does anyone have input on how to minimize the heat loss impact of adding a wood-burning fireplace to the main level?
I assume that I need to look for a fully-sealed EPA-certified wood fireplace that draws its combustion air from the outside. But do these really work or will I have backdrafting issues anyway because the fireplace doors never seal properly? I'd welcome any recommendations for specific products.
As far as installation goes, it would likely be advantageous to connect it with the slab somehow for thermal transfer, correct? FYI, the slab will be covered with tiles.

I know that between the fireplace and skylight I'm compromising the energy goals, but these will be nice features in our very simple design.

“I don't have a 'battle' with Sailor I just enjoy messing with him…” Well TLP...just know that you have been messing with a woman...and I am indeed immensely happy that I don't have to eat crow... BTW, I sincerely like the passion that you exhibit with these technical discussions even when we disagree. You may recall that I told you to hang around when others gave you a hard time.

Eljay, have you looked at masonry heaters? They are significantly more efficient and cleaner burning than any EPA-certified wood stove of fireplace that you can buy (i.e., they completely burn the wood at 1700F). More importantly, you can cleanly burn the typical small amount of wood that is required in an energy efficient house in one or two firings per day. Wood buring stoves and fireplaces typically can't be throttled back to generate these lower heat BTU levels without causing a lot of air pollution.  Masonry heaters slowly radiate heat over the course of the day and also add a significant amount of interior thermal mass which can be beneficial in a passive solar design. You can also get masonry heaters that have baking ovens (either white or black) for several hours of free oven time each day. The downside is that masonry heaters can be very expensive if you hire someone to build one. However, there are great DIY masonry heater kits these days and you can perhaps just hire someone to accomplish the external masonry work. We have more info about masonry heaters along with performance software on our website.

For fenestration sun visualization tools, this is likely the best website:

http://www.susdesign.com/tools.php

I haven't considered masonry heaters. We are familiar with them from back home (we are both from Europe), but I haven't given that a thought since they are quite massive and I think quite a heavy build. I know they would probably provide more heating efficiency, but we're after a simple and clean insert-type look that doesn't take up too much space.
But now I'm worried about breaking an air-tight envelope with a fireplace.

YES, you should be worried as fireplaces are the most inefficient way of heating a home ever invented. The reason masonry heaters were invented was because the use of fireplaces and ship building deforested the European continent and a more efficient method of heating homes became necessary. However, if you are only after the aesthetics of burning wood and you don’t use your fireplace too much, then you accept the downside of fireplaces. This is a green building website, so I feel compelled to recommend the more green wood burning solution…masonry heaters. However, not burning wood at all and using a heat pump would be even greener. Only you can determine what is the right green tradeoff and solution.

Fair points. Thank you.
Yes, we're after a fireplace for ambient fire, some supplementary heat, and a backup source in case of a power outage. On the last point, I did also consider getting a generator instead, but making that investment only to get one of the benefits above didn't make sense.
I've considered a gas direct-vent fireplace, but around here that requires an on-site propane tank with a rental fee whether it's used or not. So, it didn't sound like a good choice from an operating cost side.

Posted By sailawayrb on 28 May 2014 06:05 PM


“I don't have a 'battle' with Sailor I just enjoy messing with him…” Well TLP...just know that you have been messing with a woman...and I am indeed immensely happy that I don't have to eat crow... BTW, I sincerely like the passion that you exhibit with these technical discussions even when we disagree. You may recall that I told you to hang around when others gave you a hard time.





Eljay, have you looked at masonry heaters? They are significantly more efficient and cleaner burning than any EPA-certified wood stove of fireplace that you can buy (i.e., they completely burn the wood at 1700F). More importantly, you can cleanly burn the typical small amount of wood that is required in an energy efficient house in one or two firings per day. Masonry heaters slowly radiate heat over the course of the day and also add a significant amount of interior thermal mass which can be beneficial in a passive solar design. You can also get masonry heaters that have baking ovens (either white or black) for several hours of free oven time each day. The downside is that masonry heaters can be very expensive if you hire someone to build one. However, there are great DIY masonry heater kits these days and you can perhaps just hire someone to accomplish the external masonry work. We have more info about masonry heaters along with performance software on our website.





For fenestration sun visualization tools, this is likely the best website:





http://www.susdesign.com/tools.php

Quit yanking my chain you’re not a Sailorette, you’re a Sailor? Well good to see that my mistake, it is rare I see a woman that can handle your level of expertise. Kudo’s to you, your new abbreviated name is Sailorete, I seen someone use Sailor so I figured male.

“WE” don’t disagree, “YOU” disagree, from what I gather with lab and prototype field testing conducted across the world to validate and make sense of certain “Applied Engineering Principles” or formula’s you refer to. This line of reasoning reminds me of a college grad that passed all the calculus and physics exams and has no real life experience. Yep, many ‘licensed’ Engineers apply. Building Science is not Rocket Science, although some of can get complex like the subject of mass effect, and convective loops.

The members that gave me a hard time, it was on this subject, one accused me of being a sales guy imagine that. They, as most, did not understand the BSC “Thermal Metric Report” and how it by “hot box” testing and resulting modeling proved the impact of convective air loops and models accurate for the most part. Second to fire test modeling, convective loops are next in complexity.

We just failed a stainless steel new design @ 2000F that the FEA/CFD model and analysis showed good, so now we are back calibrating the models with test results to establish a burn rate. So no, the BSC test did not conclude what was “already known that air degrades r-value” it quantified it, just as the ORNL did mass effect by DBMS. I hope both make it to code and labeling on the manufacturing material data sheets. I’ve seen some out here that pull r-value knock down factors and assembly perm ratings out of left field that have no idea what they are talking about and their followers buy it, and their polished writing skills does not make the lack of data credible. I always know when I have exhausted a person technical argument since that is when the personal attacks or grammar attacks come.

I have not got to researching wood heaters yet but, first off I’d look at some of the net zero designs I already mentioned before that prooves them unnecessary for grid power outages. There are other renewable sources out there, along with the design of the building that is better to mitigate the need.

I think the esthetics is what draws people to open wood flames, they don’t look at the potential for CO poisoning nor care about IAQ, or like the maintenance to avoid chimney fires. Some of these DIY’ers that design and build rocket-mass heaters have no idea what they are doing. Again, it would difficult to quantify this design in a calculator, have anyone that does sign a contract with you to take responsibility for CO poisoning and fires. Gas is a cleaner safer interior burn vs mass heater smoke back.

I see a lot of round smaller contemporized ones look nice and can be placed anywhere. I don’t think an envelope penetration is a good idea for a tight home and the smaller the better. An internal wall makes more sense if you can design to code straight up and out the roof. The exhaust flue could be put in a low burn rate mass wall for mass effect just like a rock mass heater, perhaps double wall piping, outer perforated. The butterfly valve needs a good seal, like PTFE Teflon with a glass-carbon fiber filler for endurance, there are rubber polymers that take 300F. I have not got to the details and code requirements yet.

Eljay, depending on how much propane you need to use, you may be able to avoid having to rent a tank. For example, if propane is just being used for your stove/oven and as a backup fuel for your heating system, you may be able to purchase two 100 pound propane tanks (or perhaps even four 30 pound tanks). These tanks are small enough that you can take them into town and have them filled when required.

The reason you need two "banks of propane storage” is that you will want to use a switching propane regulator that will automatically toggle to the full propane bank when the propane bank that is currently being used gets low so there will never be a disruption in propane flow to the devices using the propane. These switching regulators usually have an indicator that tells you when it has toggled the propane banks so you know that you need to fill the depleted propane bank. Again, a propane bank could be one 100 pound tank or couple/several smaller tanks ganged together.

You also need to consider and properly address propane vaporization requirements. So if you elect to use smaller tank sizes, you may need to gang them together such that they will provide adequate propane vaporization to feed your propane devices. Propane vaporization is a function of the outdoor temp and surface area that the tank(s) provide.  These links contain info about propane vaporization that you may find useful: 

http://www.amerigas.com/pdfs/Propane-Fast-Facts.pdf

http://www.nbmc.com/heaters/lpchart.html

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d4500147t012.pdf

Well, ladies and gentlemen, it's showtime! We will be selecting a builder/contractor this week, so I am turning to this excellent community of professionals for final guidance to help us choose a builder.
With the final design locked down, we sent it out for quotes. Here are the packages the builders offer:

R-values: Walls/Ceiling/Slab/Windows/Doors
Builder1: R19/R50/R10/R3.6/R5 - R24 batts
Builder2: R19/R40/R15/R3.6/R5 - R20 batts + 1" exterior foam (R5)
Builder3: R19/R50/R12/R4.2/R5 - R24 batts
Builder4: R25/R60/R20/R3.6/R5 - R28 2x8 double wall (offset 2x4 wall) with 1/2lb open cell foam

To compare the insulation packages from energy efficiency, I calculated heat loss and annual supplemental heat energy numbers coming from the great calculators on Borst Engineering site:
 Walls    Ceiling    Slab    Windows    Doors    ACH    BTU/F/hr    MBTUs    kWh   Cost     BTU/hr    BTU/hr/sqft    KW
CodeMin    19    40    10    3.6    5    0.5      323    52.8     15,459     $2,203     21,945     13.3    6.4
BetterACH 19    40    10    3.6    5    0.25    263    43.0     12,587     $1,794     17,891     10.8    5.2
                                                            
Builder1    19    50    10    3.6    5    0.25    259    42.3     12,396     $1,767      17,589     10.6    5.2
Builder2    19    40    15    3.6    5    0.25    252    41.2     12,061     $1,719      17,109     10.3    5.0
Builder3    19    50    12    4.2    5    0.25    244    39.9     11,678     $1,664      16,599     10.0    4.9
Builder4    25    60    20    3.6    5    0.25    220    36.0     10,529     $1,500      14,972     9.0      4.4

Extra foam (R12)                                                    
Builder3    26    50    12    4.2    5    0.25    224    36.6     10,721     $1,528      15,254     9.2    4.5
Builder2    26    40    15    3.6    5    0.25    223    36.4     10,673     $1,521      15,148     9.2    4.4

Note: I did not include any solar heat gain. The cost is simply annual kWh multiplied by the rate $0.14251. The last 3 numbers are the design heat loss numbers. Also, I assumed that all would deliver a house with ACH of 0.25. Builder 2 & 3 both claim, they can easily get a house under 1.5 ACH50 and builder 2 has built the most airtight house in the area a few years back under 1 ACH50.

Price-wise, all are very very close except Builder4, who is $20k higher than others. While his package sounds attractive, looking at the numbers above, I'm just not sure I like the ROI on that extra cost. So, I added two more lines trying to come up with an energy difference if I were to add exterior rigid foam for an additional R12 on the walls based on Dana's recommendation from the first page of this thread. Again, I'm not sure it's worth the additional cost ($3.5k in materials alone).

When it comes to the heating system, it will be electric and between the builders and other heating contractors, the choices are as follows:
Main level + Upstairs / Energy source:
Heating1: Infloor + electric BB / Electric boiler         ~$11,000
Heating2: Infloor + Stelrad radiators / Electric boiler  ~$13,000
Heating3: Infloor + Low-temp baseboard / Daikin Altherma  ~$19500

So, at this point, I'm leaning towards the package offered by Builder3 with Heating1, which doesn't sound like a very energy-conscious choice, but I just don't see the ROI on the rest of it. :(  Am I missing something?
I'm sure that heating water with an boiler will be a killer. I wonder what the monthly bill will be. I know that Altherma can offer me some COP over a simple boiler, but at $8.5k more and assuming average COP of 2, it will likely be a 10+ years payback.

Regarding changing the roofline for future solar potential, I got quoted around $4k to change from gable to hip. So, I'm debating that too now as we actually need to cut down on the overall price of the project a bit (don't worry, we didn't spec granite countertops in the house). If solar does become cheap, rather than spending money on the roof now, can't I spend it later on a ground-based pole and mount an array on it giving me an ability to orient the panels perfectly?

There. Decisions, decisions.
Again, I appreciate all the input here and I hope you can offer some guidance on this big decision.

Curious what time period you are using for your ROI?

Well, I should have called it a 'payback period' rather than ROI to be fair.
Essentially, my comment above is comparing Builder3 and Builder4. Seems to me that the Builder4 package is "worth" about $164 in annual savings. The additional cost is $20K, so using a very simple (I know, I know) payback method, that's 122 years (20000/164).
For the extra rigid foam on the outside, if I assume it's an additional $5k and it saves an additional 957 kWh/year, in today's dollars that's $136/year. So, again a simple method would show a 37-year payback.

Is this the wrong way to make the assessment? Or are the calculated energy values suspect?

I have a hard time making sense of all the numbers. What are your expected energy costs, per year, with each method?

The problem with picking a builder based on those numbers is any one of them could simply make a product substitution and suddenly be on top. Not to mention numbers mean nothing unless the builds are exactly the same in quality.

I would be more concerned with construction details and the "how" do you plan to do this and who is doing the work, sloppy work will show itself down the road, usually after a warranty period. Good Communication between the contractor and client is the most important aspect of a build in my opinion for a successful project.

It is called a specification and one of the reasons design/build is a more reliable way to get what you pay for.

Thank you for the input. I agree with the above points and we are not selecting builder purely on the table above. Communication is a big thing and we are already leaning towards 2 of the above for that reason.
So, my question is whether, all else being equal, do those energy calculations makes sense and am I right to discount what is on paper a much better build (Builder4) because the ROI is way beyond my lifetime?

And at those heat loss levels, should I be looking at a different distribution/heating source given that we want to stick with radiant heat in an all electric house?

You might consider limiting the radiant heating to the areas where you will actually notice it and then supplement it with mini-splits (better COP) in large open areas.

Posted By jonr on 12 Jul 2014 12:13 PM
You might consider limiting the radiant heating to the areas where you will actually notice it and then supplement it with mini-splits (better COP) in large open areas.

Thank you jonr. Unfortunately, the only area where we are considering infloor radiant is the only large open area. It's on the main level (the floorplan is on page 2 of this thread).

I am trying to model the various assemblies in HOT2000 and I'm not sure how to enter a double staggered 2x4 wall with 1/2 lb open cell foam (2x8). The nominal value is R28. What would be the true whole wall value of such an assembly? ~R25?

A 2x6 wall with R20 batt and R5 rigid foam on the exterior should be around ~R19 whole wall value. However, when I entered the following wall assembly into HOT2000, it produces an R-value of R22.1. Does that sound right? Or should I just overwrite it and use R19?

Yeah, that can be problem with using software that has convenient dropdown menus for entering the building envelope layers…you may not know what it is using as R-value for the layers or if it is calculating the whole wall R-value or only adding up the R-values of the insulation cavity. In any event and with this software, at least you have the option of properly hand calculating the whole wall R-value and entering that if necessary.

Thank you.
Actually, working with HOT2000 has made me realize some mistakes I've made using your calculators. I should've read those instructions more carefully!
My previous manual calculations, results from BorstEngineering calculators, and HOT2000 results are all within ~1500 BTUs/hour, so pretty close! And the actual heat load/loss for the house is around 22,000 BTU/hr using the standard code build. When I get a moment, I will update previous posts in this thread, so future readers can follow with correct info.

Since it's time to nail down the final design, I needed to make a decision on the main roof line and decide between hip and gable roof. I have used PVWatts application (http://pvwatts.nrel.gov/) to calculate the difference in PV power production between the two roof designs. To recap:
The main gable roof orients the major portion of the roof facing 120 deg. (~SE). With the hip roof, I would be gaining roof area facing 210 deg (~SSW). That roof area could hold only three 250W (6'x4') panels. So, I have compared the power production of 750W facing either 210 deg or 120 deg. and mounted flush to the roof. The roof pitch is 5/12, so 23 deg. I've kept the default PVWatts 0.77 DC-AC derate factor.
Here are the results for annual production
750W panels oriented 120 deg, tilted at 23 deg: 715 kWh
750W panels oriented 210 deg. tilted at 23 deg: 770 kWh

The difference in potential PV production is 55 kWh or 8% better with the 750W worth of panels on the hip roof vs gable. At my current rate of $0.14/kWh, that's approximately $8 worth of electricity per year.
Now, it will cost me ~$2000 to change the roof. So, my conclusion is that it is not worth to change the roof design.

Any flaws in my analysis?

By the way, according to PVWatts, I'd need the install costs to hit $1.50/WattDC before my lifecycle cost equals my current rate of 14 cents/kWh.