Oil to Gas (Radiant Heat System)

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Dana

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At the rate cheap air-source heat pump technology is improving, by the time the Bock craps out there may be a reasonable heat pump solution for the floor.

Does it really need 140F output to stay warm when it's cold out, or would 120F do? The difference is barely consequential with fossil burners, but makes a huge difference with heat pumps in terms of efficiency & capacity.

HTP's series of rugged HW heaters and combis systems are pretty good, but you might also consider their UFT-80, which is a wall-mounted mod-con with a favorable turn-down ratio (~7500 BTU/hr out at minimum-fire), which might be cheaper. For a mod-con design they went out of their way to make installation semi-idiotproof, but that's not to say it's quite as simple as installing a HW heater solution, and truly creative semi-idiots can screw up almost anything (I'm living proof of that- just ask my wife! :) )
 

Nathaniel Hieter

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Wow, that is some detailed documentation. UFT-80 would probably be within my abilities..... with the right friend on speed-dial.

I'm pretty sure I could dial back the temperature right now. As it is, at 140 I'm having some serious over-spike during the day. If I beef up the insulation in the attic and the bedroom over the garage I dial it back even further.

I just remember those rare days when the temp dropped below zero over night and never got past 5F during the day..... it felt like the rate of heat transfer through the floor was barely compensating for the heat loss through all the glass. Now..... to be sure, when we use the radiant floor I find that my winter coat doesn't grow in quite so fast..... I end up being a bit of a softy.

A more intelligent system would adjust the temperature of the 55gal tank appropriately. I'll experiment this winter at the next cold-snap. I'll let the fire go out and dial down the temp of the water heater and see how it fares.
 

Nathaniel Hieter

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Dana, I have a confession to make: When you posted those prices for cellulose, well...... I thought you were exaggerating! I've lived in this house 17yrs and only had to go into the attic on four separate occasions. The only thing up there is the air-handler for my A/C. For $260 I get 20 bags and a free blower rental from Lowes. At a price like that I don't care if I spread a foot of "snow" I might have to swim through some day......
 

Dana

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Before blowing cellulose it's important to air-seal the ceiling plane with the appropriate materials for what it's in contact with (no can-foam against chimneys or flues, eh?). You can wrap masonry chimneys with R15 rock wool batts held in place with steel wire to avoid direct contact with cellulose.

You also have make sure the blown fiber isn't in contact with the roof deck at the eaves. Code-demands a 1" clearance. While there are cheap foamy chutes purpose-made for the application, they're pretty crummy. The asphalted cardboard versions are far better.

Make up a set of cardboard depth gauges marking the depth range of what you're going for stapled in place in such a manner that they're not easily blown over, and rake the top of the material level with your marks as you go. Invest in a decent respirator mask- not just a crummy nuisance dust mask, and wear safety goggles. There's a lot of dust in the air when doing open-blown cellulose, most of it fire-retardent. If you can, order up some "borate only, sulfate free" cellulose- most off-the shelf goods at box stores uses sulfated fire retardents in combination with borates. Sulfates are far more chemically active with things you care about, such as nails, wires, lung linings, etc. While they're fine when dry, a slow roof leak could lead to a stinky corrosive mess over time, which is NOT a problem with borates. Most "stabilized formula" cellulose products designed for damp spraying are borate-only, primarily because it smells a bit like cat-piss when it's still damp, which isn't a great selling point. :) The stabilized formula goods have a water activated adhesive to limit or prevent the material from settling over time, but it's fine to install it dry too- there's no real benefit to renting the much more expensive damp-spray equipment for an open blown attic.
 

Nathaniel Hieter

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Hmmm. The price of rolls of unfaced R30 seems competitive with the "friendly" version of cellulose. I would still air-seal the attic, but instead of removing the old two layers of R13, I would just run the R30 perpendicularly on top of the roof deck. I suppose I should still put in the proffer vents so that I can tuck the R30 down into the eaves.

I also noticed that my two upstairs bathroom vents are just blowing into the attic. I'll be venting them out the gable end.
 

Dana

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R30 fiberglass batts are more subject to voids & compressions than blown insulation, is somewhat translucent to infra-red radiation (an important performance difference under a 130F roof deck in summer), and is nowhere near as air-retardent as blown cellulose, which means it loses some performance to convection in winter when the bottom side is warmer than the attic, unless you install a top-side air barrier.

If you're going with fiberglass you're better off with the chunky type higher density fiberglass blowing wools (eg: Owens Corning AtticCat, sold at most box stores) than with low and mid-density batts, but that's ususally more expensive per R than cellulose, and has far nastier dust (fiberglass particles) during installation.

With any new insulation (cellulose, batts or blown fiberglass) it's fine to leave the R13s in place and just bury them.

The bath venting is best done through the roof rather than the gable, unless completely sealed and buried in or under your insulation so that it stays warm, with enough slope that any condensation runs back toward the fan. When the vent pipe is cold in winter condensation, (even frost ) will form, and in a horizontal run it will corrode the vent, and drip into your insulation & ceiling somewhere along the path. With a vertical run through any condensation either goes out the top or back from whence it came, which is much more manageable. The vent should still be insulated, which won't affect the initial condensation, but as it runs longer it allows the pipe to warm up, purging the majority of the moisture to the outside.
 

Dana

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The box-stores won't special-order it for you?

Greenfiber (often carried by box stores) manufactures stabilized formula borate-only goods. If you paid up front I'd think the local box store could get some on the next truck from the distributor.

National Fiber (HQed) in Belchertown MA only uses borates. "Cel-Pak" is the product name of their standard dry-blow product, sold through many of the regional distributors catering to the trades (rather than box-store retail.)

There are others.
 

Nathaniel Hieter

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Dana, I'm not sure if you are still following this thread. On the off chance, I will post....

Sadly, this project took an.... unexpected.... detour.

Before I elaborate, let me first say "Thank you"! I implemented several of your suggestions and the benefits were immediately apparent. Unfortunately, we did not have very long to enjoy the fruits of our labor: In late January a fire destroyed our home. We are so very grateful that our suffering has been only emotional: Wife and kids and I all made our escape without even burning a hair.

When these things happen we all look for the "silver linings". The big silver lining in this case is that we got a construction "Do Over". Sure, I'd rather have my childhood pictures and family heirloom antiques, but in the meantime I'll be working hard on the lemonade.

If you will indulge me, I have two questions for you:

(1) Every friend of mine that finds out I am rebuilding seems to work in the words "spray foam" in every other sentence. It makes me lean towards double-stud-cellulose out of sheer stubbornness. However, I worry about moisture build-up on the interior of the sheathing. When my friends aren't talking about spray foam, then they are talking about Zip sheathing.... but I'm pretty sure that is OSB which makes me nervous. In concert with an HRV, can the cellulose provide a reasonable absorption "buffer" to allow cyclical drying? Will air-sealant tape stick to traditional plywood or is there something special about the Zip surface that enhances adhesion?

(2) Given that I have 10kw of solar panels and dual-axis trackers, I would love love love to have an electric-only heating solution. I've been promoting an air-delivery system to the wife..... but I have been unsuccessful so far. Sigh. I'm still holding out hope, but I figure I better plan for failure. If I go with the $$$ warm board product (or something similar?) I'll be able to use a far far far lower water temp than my old DIY system, especially when we consider that I'll have better insulation and smaller (and better) windows. Does that put the "chiller-only" within the realm of possibility or do I need a propane backup solution?
 

Dana

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I'm very sorry to hear that the house is gone! (At the same time, I'm glad to know that you're still with us!)

ZIP is an OSB product that is manufactured with a pre-applied weather resistant barrier (no housewrap or #15 felt necessary.) It's a decent product, but not necessarily the way to go. One advantage of ZIP over other OSB is the ease of air-sealing the sheathing layer using their proprietary tapes to seal the seams. While sealing the seams is necessary, it's not sufficient. The framing still needs to be sealed to both the sheathing and the foundation.

In US climate zone 6 a 2x4/R13 + R10 continuous insulation would meet IRC 2015 code-min per TABLE N1102.1.2 (scroll about half way down the page) and would have plenty of of dew point control without need of interior side vapor retarders tighter than standard latex paint per Table 702.7.1 (about a quarter of the way down this page.) With a 2x4/R10 + 10 stackup you could use either damp sprayed cellulose, dense packed cellulose/fiberglass or open cell polyurethane foam, in the cavities, which ever is cheapest (probably damp sprayed). Cellulose would offer the best moisture resilience, 1.8lb fiberglass or 0.7lb open cell foam would have a (very slight) performance edge.

Closed cell foam between thermally bridging framing is a waste of good foam, and very expensive- not worth considering as cavity fill. Spend the foam budget on continuous exterior foam where it's performance isn't being cut off at the knees by R1.2/inch framing. The "whole-wall-R" of a 2x4/Rxx + R12 wall is about R22-R23-ish, independent of cavity insulation type.

For the exterior foam in your climate 2" foil faced polyiso (labeled R12-R13) would be the easiest to build and is easy to air seal with foil tapes. An alternative would be 3" EPS (labeled R12.5-ish) which would outperform the polyiso in mid-winter but underperform it slightly in summer. Polyiso needs to be derated to about R5/inch for heating season performance in your climate in this type of application, since it underperforms it's labeled R at the cold temperature extremes. EPS outperforms it's labeled R at the cold temperature extremes. A 2x4 wall with 2" of exterior polyiso is the same wall thickness as a 2x6 wall, but has only 2/3 the heat loss of a 2x6/R20-23 wall (which meets state code for zone 6 in states still operating under IRC 2006 or 2009), and is inherently far more moisture resilient.

If you're thinking about double-stud walls or other high performance walls, take the time to ponder this document.(including the hygric simulation analysis.) A double studwall with VENTILATED siding and and 2-mil nylon (eg Certainteed MemBrain, costs less than 15 cents per square foot) as the interior vapor retarder under the interior gypsum and detailed as an air barrier it almost wouldn't matter what the cavity fill was. But cellulose would offer the most resilience, as well as a measurable thermal mass benefit once you're at 6" or thicker 3.5lb cellulose. You'd also do OK using "vapor barrier latex" as the vapor retarder, but in your climate zone there still be some risk if with only a standard latex paint & vented "rainscreened" siding alone.

If you're considering taking it to Net Zero Energy, review the whole-assembly-R values & U-factors in Table 2, page 10 of this document.

If you're going for R25+ whole wall and smaller higher performance windows, with a Roth panel or WarmBoard approach you'd very likely be within range of a 2 ton Chilltrix, but keep running the load numbers on the house as you tweak the design. Now is the time to register and download a copy of BeOpt and get familiar with how to use it (I'm not an expert on it myself- yet), which makes it much easier to play "what if?" games with design changes to figure out both energy use and peak loads, both of which are important. But you can still do a lot with an I=B=R type spreadsheet heat load calculator, if tools like BeOpt aren't your cup o' camelia sinensis.

With a high-R house that isn't quite covered by the output of a chiller-driven radiant floor, cold climate mini-splits sized for your cooling loads would more than cover the difference (or even the whole thing), not need for propane backup. As a "Hail Mary" back up for power outages an EPA rated wood stove may not be a bad idea, and for a high-R house it doesn't have to be very big at all.
 

Jadnashua

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If I were going to build a new house, I'd use either engineered panels (OSB-foam-drywall or some other outside layer) or stack it up with ICF blocks all the way to the eaves. Pump it full of concrete and you have a huge, insulated thermal mass. You can get panalized floors and ceiling, too. Once the footings are in, you can have the whole thing enclosed very quickly, already insulated, with the doors and windows openings (computer cut at the factory) perfectly sized and placed, perfectly flat and plumb. If you go with ICF, one way to make wiring and plumbing runs easier is to use horizontal strapping, creating easy runs while offering a means to attach your desired interior finish.
 

Nathaniel Hieter

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Dana, lots to read.... still digesting. I'm definitely looking at high-performance walls. I'm sure I'll have some follow-up questions and I read more...
 
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