This is probably a dumb question, but... As R-value doubles, the amount of heat loss is halved? So, for example, all else equal*, the impact of upgrading from single pane windows to dual pane would approx equal the effect from taking walls from R11 up to R22? * e.g., if the btus needed to heat the home were the same from the walls as from the windows (meaning a lot of glass). I ask because I've been poo-pooing the huge expense of upgrading our beautiful stained wood windows and french doors, thinking it's only a rise of R-1 to R-2. But as I look at our heating load numbers, windows/doors are more than for the walls and ceiling.

Yes, everything should be compared on a BTU (or ROI) basis. Also consider things like solar gain, IR loss, comfort and air leakage.

Doubling the R value will halv the heat transfer RATE. IF you have single pane windows now, upgrading the windows could possibly be more like a factor of 4 or 5 increase over your current window R value. Single pane glass has a U factor around 1.2 ish? R is the resistance to heat transfer, U is the actual transfer rate in BTU, per SQ/FT, per degreeF of temp difference, per hour. You can convert back and forth between U to R by inverting the number(dividing it into 1) 1 divided by U1.2 = R0.83. A double pane U0.3 window would be R 3.3 or nearly 4X the resistance to heat transfer as the single window.

Air infiltration can quickly dominate the heat loss equation in a house. With older leakier windows, you could be loosing as much heat in the form of air infiltration as from the insulation properties of single pane glass. Newer tighter windows would probably cut the air infiltration down and yield added savings beyond the R value increase...

It's pretty common for windows & door losses to be higher than wall losses even in new code min houses. For houses with single pane windows it's nearly always the case, even when there is no insulation in the walls or attic.

Single pane windows suffer from both high operating cost AND low comfort levels, in any US climate. Bumpting an R1 window to R2 is HUGE improvement on both operating cost and comfort, compared to taking an R10-ish whole-wall-R like a 2x4/R13 type wall up to R20-ish (2x6/R20 + R5 insulating sheathing.) It's like anything else- if you aren't addressing the biggest part of the problem, the rest doesn't matter very much. Take air-sealing- an R50 wind tunnel leaking 30 ACH/50 isn't going to be very comfortable or cheap to condition despite the R50 envelope.

Looking at R-value merely on a net-present-value of future energy cost savings basis isn't always the best framework and can be short-sighted. There's comfort value in the higher wall temperatures, and when looking at an exterior insulating sheathing type stackup there is enhanced moisture resilience of keeping the structural sheathing a few degrees warmer (=drier.) But like anything else, there is diminishing returns there too.

In 2010/'11 folks at Building Science Corp did a rough outline of what it would take to hit Net Zero Energy fairly reasonably in any US climate zone, which is in some ways an upper bound on what makes lifecycle economic sense. As PV gets cheaper and heat pump technology more efficient, the additional lifecylec cost of the marginal increase in whole-wall R crosses over the lifecycle cost of the PV + heat pump needed to supply those loads. There's a good case to be made that PassiveHouse levels of insulation are quite a bit beyond that point. See Table 2, p10 of the BSC's BA-1005 document, downloadable from this page:

http://buildingscience.com/documents/bareports/ba-1005-building-america-high-r-value-high-performance-residential-buildings-all-climate-zones/view

In locations with very cheap energy and high building costs hitting those whole-assembly R values (all thermal bridging factored in) may not prove to be cost effective on an NPV basis, but in high energy cost low construction cost areas going a bit higher is still "reasonable" on a lifecycle cost basis, even under projections of future energy price deflation based on cheaper PV & higher efficiency heat pumps.

Thanks for the detailed and excellent responses. I have quite a bit more math to do. Excellent point, Dana1, about the relative costs/benefits based on construction and energy costs. We're in the unhappy situation where BOTH construction AND energy costs are high (highest electricity in the country). To change the glass, we'd have to rebuild with new sashes and doors and stain them ($100k+) OR spend about $50k on solar + maybe $25k on ASHPs to "BTU my way out of the problem." We're very poorly insulated, but I can only improve about half of it (the rest is impossible, due to vaulted ceilings with tongue/grove and tile roof right over it). Still a relative no-brainer to address that regardless.

One point about the windows. They are TIGHT. Mostly because they're from '05-'07 (don't ask me how they get them past Title 24), custom hand-built stained wood. The previous owners spent a ton on them. The six sets of french doors are of the same design, but nowhere near as tight, as single point double doors often aren't.

Your electric rates are not the highest in the country, not even as high as Connecticut or New York, and nowhere near those of Hawaii (at 34 cents/kwh AVERAGE), even if your highest tier marginal rates are comparable to or higher than the HI avearge. (I'd bet their construction costs are higher too.)

http://www.eia.gov/electricity/state/

Limiting the number of windows that you open for ventilation and adding interior storms can make a big difference without much difference in appearance. Interior storms can be removed on windows when you need to open them, or installed only seasonally if you like. They don't have to suck from an aesthetic point of view- there are some pretty good ones out there that practically disappear, and it'll be less than $200 per window even in high-cost areas.

I'm not sure what you can do about the French doors though. Reliable weather stripping is an issue with any door, but even harder to get right with double-doors.

The notion that you can simply BTU your way to comfort isn't really well founded. You have to raise the mean radiant temperature, which means either massive use of radiant floors &/or ceilings, and/or fixing those pretty R1 holes in the wall masquerading as windows.

I'd be surprised if it took anywhere near $25K of ASHP to heat & cool the place, unless you're talking low-temp hydronic heating with radiant floors (in which case it'll be more than $25K as a retrofit heating SYSTEM, not just the heat pump.) Ducted or ductless mini-split solutions would likely come in under $15K if well specified in advance, and bid competitively.

Six "sets" of french doors? Are you using all the french doors? You might also be able to "storm over" some of those as well to improve your air infiltration.

I should have said "among" the highest energy costs. We're .43/kwh after a relatively low amount of use. What's relevant is that any heating solution involving electricity will be in that .43 tier. Thus, energy is very expensive for us.

Storm windowing is viable for a few of our windows. The French doors, no. Even getting those things to loosely seal is hard -- the tolerances are tight, and no weatherstripping I have found is pliable enough to seal and still allow the doors to close. Along the bottom is even tougher, especially where they meet. Boy do I miss my multipoint Loewens from our previous house. Tight!

We definitely can BTU our way out of it. When we crank the propane FAUs and let the temp get really expensive, the house feels fine. For awhile, that is!

As for the ASHPs, the $25k might be low based on initial feedback here. The combination of 2 or 3 units, plus 6 heads that need to be recessed into walls to hide them... that stuff adds up.

what is the goal - to increase comfort, to be netzero, etc. ?

do you have A/C in the house - I'm assuming A/C is a big part of your power bill there?

Just a thought, because the ASHP are very efficient at air conditioning as well. Have you factored their cooling efficiency into the equation over what you have now?

I would think that A/C is a larger bill than heating, but i have no idea (assuming SD = San Diego?).

Before I moved here, I thought for sure it would be all about cooling. Wrong. Nearly zero need for a/c, with only a few days here and there in July-Aug where the house breaks 80F inside. Our highest electric bill was about $230 (for 4000 sq ft, 1000 sq ft guest house, pool, and lousy insulation). The goal is to be comfy for the 4 months in which we currently freeze, and at the lowest cost. We're caught in multiple catch-22s because *everything* is expensive. ASHPs sound great, way better than propane FAU, BUT with electricity at .43/kwh, it's probably no savings, and consequently we'd likely still stay cold. So we "need" solar so we have an all-you-can-eat electric bill ($0). BUT, that's $50k because of our very complex installation needs on a tile roof. OK, so then maybe approach it from the opposite direction and improve insulation and sealing ($20k), ducts ($8k) with no assurance of great improvement because of the areas we can't insulate and all our single pane. So we might have to replace all the window sashes and doors ($100k+). That could pay for a LOT of propane over the years! Sorry for the complaining. I'm just so angry with the previous owner for cutting corners (none of which could be detected reasonably in inspections).

Posted By AztecSD on 04 Jan 2016 08:51 PM
I should have said "among" the highest energy costs. We're .43/kwh after a relatively low amount of use. What's relevant is that any heating solution involving electricity will be in that .43 tier. Thus, energy is very expensive for us.

Storm windowing is viable for a few of our windows. The French doors, no. Even getting those things to loosely seal is hard -- the tolerances are tight, and no weatherstripping I have found is pliable enough to seal and still allow the doors to close. Along the bottom is even tougher, especially where they meet. Boy do I miss my multipoint Loewens from our previous house. Tight!

We definitely can BTU our way out of it. When we crank the propane FAUs and let the temp get really expensive, the house feels fine. For awhile, that is!

As for the ASHPs, the $25k might be low based on initial feedback here. The combination of 2 or 3 units, plus 6 heads that need to be recessed into walls to hide them... that stuff adds up.

First, you can't recess ductless heads into little cubbys and still have them work effectively.

Second, the head per room would be extreme overkill for your still pretty low room loads (have you done a room by room Manual-J), which adds cost, reduces efficiency, and even reduces comfort.

Since you have a crawl space, a mini-duct cassette solution is almost certainly possible for the first floor. There may be similar possiblities where there are attic spaces.

With a proper heating/cooling load calculation it's possible to estimate just how much of the power would end up in the highest tier. It's probably possible to install PV cost-effectively to cut into that high-cost power too, since the levelized cost of PV (even without subsidies) is well under 43 cents, it's less than half that. With subsidies it's more like 1/3 that amount. If you don't want to buy PV, there are at least a dozen companies that would line up to install it for $0 down, cut you a PPA (power purchase agreement) for under 20 cents for that output, maybe even under 15 cents.

Fix the holes in the building envelope first (both thermal insulation and air leakage), since that buys you more comfort than simply more BTUs paid for with more PV. In my area you can get five tons of mulit-split with six zones for about $15K in competitive bidding. It's highly unlikely that you need anywhere near that much raw BTU output, or that number of zones to keep it comfortable. Hire an energy nerd to really run the room-by-room load numbers of the "after" picture of any building upgrades. Only then can you have an intelligent conversation about what it takes to cover those loads, and what it costs to install or operate.

Hire an energy nerd to really run the room-by-room load numbers of the "after" picture of any building upgrades.

Preferably one that isn't trying to sell you any of those upgrades. Even better if he uses a freely available program (like BEopt) and shares the data.

What is the efficiency of the heating system in the home? Sounds like propane forced hot air?

Is it modulating with a variable speed blower?

I'm not saying not to address the insulating and sealing...just curious on the furnace.

If it's single stage and single speed blower, there could be some comfort to be gained there.

That's why you hire a HERS rater or an engineer whose business is the accuracy of their numbers (and not an HVAC or remodeling contractor) to to run the Manual-J.

Also, if you don't think you want PV messing up the aesthetics of your property you can buy or lease into a community solar project at WELL under 43 cents/kwh. PLEASE give up the notion that you're somehow a victim of high electricity prices due to the tiered rate structure and the high top tier marginal rate. In California you have more options than in most states due to the strong policy support for distributed renewable power, and it's more affordable than the highest tier rate. The reason the average residential retail price of electricity in CA is lower than it is in MA is because even if you're a heavy electricity user you really don't have to pay the highest tier unless you're unwilling to go out and find the cheaper alternatives.

The combination of 2 or 3 units, plus 6 heads that need to be recessed into walls to hide them... that stuff adds up.

Given that you have an existing heating system that can heat closed off areas, you are in a good position to use far fewer heads. Your mild climate also helps with heat balance. In other words, you might find that two small single head ASHPs located in open areas, open interior doors and couple of degree bump in open area temp allows you to move significant load from propane to the heat pumps.

And as mentioned, you might use one ASHP to over-heat an insulated crawl space. Little equipment, no visual impact and radiant comfort.

I'm guessing that AztecSD prefers to suffer since gives him an excuse to complain, about energy costs, aesthetics, all sorts of good stuff to keep the misery going. :-)

Seriously almost no houses in San Diego County would be well served by six multi-split heads. At his likely 99% outside design temp of ~40F most decent mini-splits would have a heating capacity of 18,000 BTU/hr per ton or more, and even a pretty leaky house would have a heat load of about 10 BTU/hr per square foot of conditioned space. (Some 3/4 tonners would put out that much.) That means 1800-2200 square feet could be heated (but not necessarily cooled) with a single head 1-ton mini-split.

A 2-ton multi-split would be able to deliver at least 12-15, 000 BTU/hr per ton @ 40F, and would be able to heat (but not necessarily cool) something like 2400-3000 square feet of conditioned space. Two tonners are about the smallest 3-zone multi-split out there, and their mini-modulation at +47F is something like 7000 BTU/hr.

Assuming it doesn't have a ridiculous amount of west facing glass the cooling loads are probably going to be ~1200-1500 square feet of conditioned space per ton pf compressor, so a 3000' house (isn't that about how big this house is?) , may need 2 or 2.5 tons for cooling but probably not 3 unless it has extremely high afternoon solar gain characteristics. (And don't tell me that it has high afternoon solar gain unti l/ unless there are load calculations to back that up.)

The smallest multisplit heads can deliver 7500-8000 BTU/hr @ 40F, which is WAY overkill for any single room load in that climate ('ceptin' maybe a Great Room), but Fujitsu recently released some 7K mini-duct cassettes that can easily split out to serve to 2-4 adjacent rooms mounted in the tops of closets or a built-out soffit. A 2-ton multi-split and three 7k-12K mini-duct cassettes can serve a LOT of rooms without having to build out duct chases or cubbys, if you can figure out where to tuck the mini-duct cassettes. (Under the floor in a crawl space is good, as is up in an attic if you keep the duct runs short and air-seal the hell out of both the ducts & cassette and the ceiling penetrations.)

But until there are some sorta-real load numbers it's hard to say for sure where it lives on both heating & cooling loads, or what might best serve those loads. But 6+ heads, each 3-4x oversized for the room/zone loads is an inane "solution" to this problem, though I'm sure there are HVAC pros who would be happy to sell you a system like that (so's they can keep current on their boat payments.)

Posted By Dana1 on 06 Jan 2016 11:19 AM
That's why you hire a HERS rater or an engineer whose business is the accuracy of their numbers (and not an HVAC or remodeling contractor) to to run the Manual-J.

Also, if you don't think you want PV messing up the aesthetics of your property you can buy or lease into a community solar project at WELL under 43 cents/kwh. PLEASE give up the notion that you're somehow a victim of high electricity prices due to the tiered rate structure and the high top tier marginal rate. In California you have more options than in most states due to the strong policy support for distributed renewable power, and it's more affordable than the highest tier rate. The reason the average residential retail price of electricity in CA is lower than it is in MA is because even if you're a heavy electricity user you really don't have to pay the highest tier unless you're unwilling to go out and find the cheaper alternatives.

Ductless heads recessed... I was unclear. We would use what they called a "pancake unit" in the attic, and duct it from there (under 10') to a standard-looking register. We would remove all the propane-driven ducts and furnaces. Installing PV... our installation isn't just about aesthetics, is about the practical challenges of putting panels on a tile roof in a way that the town will approve. Adds $25k over a typical install. Depending on how you do the math and the usage assumptions, yes, we get under .43/kwh with it. I looked into community solar, etc. several months ago, and it wasn't really available here. But true, there are ways we can reduce our marginal rate below the rack rate .43. Fixing the holes in the envelope first... makes sense intuitively, however even the guys who propose the work ($20k) say we may not notice that much additional comfort thanks to all the single pane glass and the 1/3 of the ceiling that can't be insulated at all. No one seems to know whether that's our best spend or our worst. 5 tons for $15k ASHPs... You may be in a much less expensive area than San Diego (unrelated, but I was stunned to see gas in New Orleans for $1.69 last week, when it's $3.39 here). I should have their proposal in a few days and will report back on it. Energy nerd for heat load calc... Got one, done.

Sorry about the lengthy paragraph. I insert spaces and it all clumps back to one block of text.

Dana, I hate it when people figure me out! :-)

House is a bit over 4000 sq ft, with 10' to 15' ceilings.

I WISH we had lots of solar gain. We don't. Not much west-facing glazing at all.

Posted By patonbike on 06 Jan 2016 11:11 AM
What is the efficiency of the heating system in the home? Sounds like propane forced hot air?

Is it modulating with a variable speed blower?

I'm not saying not to address the insulating and sealing...just curious on the furnace.

If it's single stage and single speed blower, there could be some comfort to be gained there.

Propane FAU. One is 100k (single stage) and the other 75k (2 stage blower), both are 80% efficiency.