Does parking a recently driven car in an attached garage warm the house?

One thing worth noting since it is relevant to the water heater: electric water heaters have an insulation advantage since they can be insulated on all external surfaces. As I understand it this is a portion of why they have efficiencies in the 90+% range while traditional gas water heaters with the same insulation thickness are in the 60+% range. (The other major factor being hot flue gas losses in non-condensing designs.) The flue pipe through the center plus less/uninsulated sections on both heads drop the average R value for the overall envelope of many gas heated tanks.

However, the overall efficiency of the electricity production/distribution is much lower than that of using nat. gas for fired heating, so the tank losses don't come close to covering the final energy efficiency of a gas system.

It is hard to see how tankless electric heating would be a winner since tank losses are so low for an electrically heated tank. Tankless gas heating on the other hand has potential because the losses can be so much greater. A condensing gas water heater would seem to bridge much of the efficiency gap, while still providing a storage reservoir, as well as the option for thermal solar connection.

The other thing that would scare me away from tankless electric water heating is that where I grew up the well water was nearly saturated with calcium and magnesium carbonate. I can't imagine an electrical element surviving long at high fire rates. I recall blowing down, draining, and scraping the water heater elements in home and barn about once every 6 months (about a bucket full of deposits each time...a tablespoon at a time), and double elements still burned out every 3 years or so.

Maybe I'm missing something, but that is my take on it.

 

Exactly the case. I gave recirculating pumps a thought, but the amount of time we actually use the heaters is small. The one on the MIL addition covers our bathroom and the laundry. Weekends is when it gets the most use, during the week, only in the mornings for roughly 10 minutes while we shower, the rest of the day it isn't used. The one at the other end of the house, is roughly used once or twice per day, and that includes the weekends, it supplies three bathrooms. The kitchen gets the most use, but there was no practical way to install a tankless unit there, not close to the gas line, and no room for the flue. The easiest way to install this was to tap off the main water line and install the tank. We had redesigned the kitchen from the original floor plan, which was itself a redesign of the original floor plan, and we dont have a clue where the original kitchen was located. We moved the sink from the middle of the house to the outside wall, where we could vent the cooktop, and it made for the perfect kitchen triangle. In either case it was a good 40+ feet from the water heater. It took at least 2 minutes or more before there was hot water coming out of the faucet. I looked into the recirculating pump, but since we were going with the tankless, we decided to use tankless for all three areas, and thats how we wound up with the electric water heater under the kitchen. It is a GE 38 Gallon 9 Yr warranty heater, and of course now the recirc pump kits are less expensive and easier to find than they were 6 years ago. My next goal is installing new windows throughout with triple pane low E glass. I already have 30" of insulation in the attic. Ultimate goal is to reduce the amount of LP we use during the winter, it is Very Expensive.

 

Two thoughts,
Probably too late for a variety of reasons,, but first, some of the newest demand water heaters will vent out a side wall through a simple hood, so gas line issues not withstanding, you might not have a problem venting a kitchen unit.

Second, I suggest that you carefully at the economics of triple glazing. While, (as you may have gathered) I am a huge proponent of saving energy, triple glazing MAY NOT be the most cost effective way to go forward.

Few people understand the issue of R-value/U value in glazing structures. In (very) simple math, any glass by itself has almost no R-value, and a very high U-value. (R is the resistance to heat flow, U is the actual heat loss in btu/hour/delta T) What gives any glass any R-value at all is the film of still air on the inside and the outside of the glass. If you take away that film of still air on one side you reduce the R-value to ~1/2. Take it away on both sides and the R-value is almost zero.

So in said simple terms, (assuming still inside and outside air(s)) a single glazed window will have an R-value of ~ R-1 Add double glazing and you increase that to ~R-2. Now if you go to triple glazings you will go to ~R-3. Sounds pretty good, loosing ~1/3 as much heat as single glazed but consider this: If there is a breeze out side, and your forced air furnace is moving air across the glass inside, you have a net/net ~R-2. ( I know that exotic gasses and low-e have a small net increase in R-value but in the real world the effect is in fact quite small, perhaps a total of R-1 (additional) on a triple galzed window, I'm just trying to keep the story simple).

So now, lets say that you are going to spend $3000 for example to upgrade your windows, and that after tax credits/rebates etc your net cost is $2000. How many BTUs are you going to save over the course of a year? For the same $2000 are there other things that you could do to your house to same MORE BTUs? In your case, you have already added insulation and hi-ef appliances etc and maybe this is the last thing to do, and for that I applaud you, but for most houses there are lots of things that would make better sense to do first. Even in a well built, well insulated house, ideas like air/air heat exchange, grey water heat capturing systems/earth circuit heat pumps and on and on.

A much simpler/more efficient (and cheaper) way of saving BTUs is to make/build insulated window quilts/night shades. These can have an R-value as high as you like, but ~R-10 is pretty easy to do,, thereby saving at least 3 times as many BTUs as triple glaze, 5 times as many as double glaze,, at ~1/4 the cost.

One final note, I suggest to anyone, if they have single glazing, then the first thing to do is go to double glazing. At that time it MAY be cost effective to go to triple, but if you have double already, certainly consider if it is the best use of your conservation dollars.

Icarus

 

There is a day and night difference between double and triple glazing. For temps <-25 C triple glazing is much less drafty, not near as much condensation

Tri-panes are much quieter too

 

Jay,

Once again you are right, they are indeed less drafty, and condense less at -25. Two notes however, most folks don't live in Winnipeg or routinely have -25. Second as I suggested greater energy savings could be had cheaper doing other things. (possibly) For example, lets say that adding triple glazing cost $10k and it saves 200,000 BTUs a year. Now if you could add 6" of insulation in your attic for $2000 (or something else) and save 300,000 BTUs it might make better sense.

All I am suggesting is that people look carefully at the numbers before committing to a strategy. (Window sellers won't usually suggest you buy R-10 window quilts instead!)

Icarus

 

First, I understand what you are saying about cost effectiveness of various incremental changes. However I'm going to have to nit pick some of this. You won't eliminate the boundary layer through air movement. It is still there but it becomes thinner as velocity increases. And there is natural convection occuring (assuming there is a temperature differential) even with no other form of air movement.

There is no way the blower is going to move air at sufficient velocity to effectively eliminate the resistance of that inner boundary layer unless the discharge is direct and undiffused directly onto the glass. Getting a decent film heat transfer coefficient (reciprocal of R) with a non-condensing gas at atmospheric pressure is difficult. Yes, R at that boundary will decrease fractionally, but there isn't going to be any velocity to speak of so natural convection is likely to exceed it.

Externally is a different matter as winds and/or rain can reduce the resistance to a much greater degree. That one could be driven low enough that zero is a reasonable approximation.

Heat duty with R10 = 1/10 = 0.1 R3 = 0.333 R2 = 0.5. R1 = 1. So the reduction in going from single glaze is:
Double glaze = (1 - 0.5)/1 or 50% (half the duty)
Triple glaze = (1 - 0.333)/1 or 67%
R10 shade/quilt = (1-0.1)/1 or 90%.

You don't save 3 times as much as triple glaze compared to single, but you will lose ~3 times less with the quilt than triple glaze.

The first few R units are the most critical. It's like mpg analysis because it is reciprocal in nature. Going from 15 to 30 mpg is huge. 50 mpg is nice, but the potential savings going from there to 100 mpg are much less.

I've not looked at the incremental cost of various window options so I can't speak to the cost effectiveness of triple vs. double. However, an easier way to look at this is in comparing total window area vs. total wall and ceiling area. A relatively small section of R1 or R2 will hammer the envelope's overall R value. Going from R30 to R100 in the attic isn't going to have as much impact as reducing the losses in what amounts to a large hole in the envelope. And areas with high losses feel drafty.

In winter I want the sunlight to enter. Do the quilts let the light in? If not the triple glazing for those windows will be far superior. In summer I turn the shades to block much of the light.

 

Shawn,

You make some great (albeit esoteric to most) points. With out going into vast technical engineering let's just accept that Single glaze is for the purpose of this discussion is R-1, double R-2 triple R-3.

Your point about window quilts is well taken. I am suggesting that night shades/window quilts will only have an effect while drawn (at night!), so the calculated benefit should consider that as well.

My entire point (as you well understand) is if the goal is to reduce to the barest possible minimum, the heating load of a structure (taking life style into account) then it is POSSIBLE that there may be better ways of doing it than triple glazing.

Proper glazing design should take into account solar gain (both desired and undesired) as well as heat loss from the building envelope. Too often we look at prescriptive solutions rather than perhaps looking further out the box.

Icarus

PS I am not an engineer, only a retired builder who has an opinion on way to many things. I do have some considerable experience designing and building passive solar houses as well as off grid Pv.
And, above all else,, my math skills suck!

 

When I built my hobby farm home, I went with windows from Polar Windows and Doors. Since I used ICF walls, the finished wall width was 12 inches. They offered PVC windows with proper jambliners, drywall edge channels, etc

For the entire package, the difference between dual pane, Low E, Argon fill, and tri pane (Also dual Low E and dual Argon fill) was 12% more for the tri-panes

It was a no-brainer decision

Even if you don't require that sort of performance in a moderate climate, the windows are MUCH quieter. Whether bratty neighbor kids playing on the street, lawnmowers, etc, tri-panes are much quieter compared to dual panes

 

Jay,

I absolutely agree in a new construction application,, it is a no brainer in a cold climate,, the price differential is so small to be almost insignificant on the total cost of the structure.

Perhaps I should have been more clear in my point. If you are considering a retrofit that includes tearing out and replacing double pane windows (that you have already paid for) and essentially paying again for window, there MAY be better alternatives.

Now the calculations might get a bit murkier if you were to leave the existing double glaze in place, and ONLY add a storm sash the numbers change again,,,

Icarus

 

Well guys, thanks for the tips, but when one double glazed window has a soccer ball size hole in it(darn kids), any glaze would be better! Actually the windows I had in mind weren't exactly three panes of glass, but two panes with a plastic film in between. The windows being replaced are 72" x 48" for two of them, and two more that are side by side same height, double width, and all are lower casements. They are set into a brick fascia, so replacing them will be a pain, and the wall thickness is odd since there are two sheets of 3/8 drywall on the interior walls, plus the depth of the bricks. I am not looking forward to it, and I am still working on getting my roof done, It looks so easy to do, until you get up there and start doing it by yourself.

 

Those are "heat mirror" windows

http://www.westislandglass.com/heatmirror.shtml

In the late 1980's they were briefly popular in Canada, as a lighter alternativet to tri-panes. However, the performance didn't quite measure up to a good tri-pane, and their popularity dropped off the radar

My windows are tri-panes, with dual Low E, and dual argon fill. Even at -40, there is hardly a trace of condensation on the window

 

Of course the level of condensation on glass is a direct relationship between the temperature of the glass coupled with the indoor relative humidity.

For example, since you are in the dry prairies, you relative humidity is pretty low in the winter. So taking 30% rh at 20C, and passing that air over 10C glass might not reduce the air to the dew point.

Now if you are in the Pacific N.W and your indoor rh is say 75%,@ 20C and you pass that air over a 10C glass you could indeed get the air to the dew point, and condensation will occur.

The number of glazings is only relevant to this issue is that it has the effect of raising the glazing temp, ergo raising the dew point of that glass.

So single, or double or indeed triple glazing isn't really the issue.

Just picking nits,

Icarus

 

I'd see a doctor about that

Seriously though, in temps of -25 C, especially -40, a good tri-pane window is hands down better than a good dual pane.

My first condo in Winnipeg, had dual pane windows. If I didn't put up plastic window film, by the time the temps got down to -25 C, I'd have not only condensation, but ICE on the lower edge of the window

They did a major renovation while I had that condo, and went with Polar tri-panes. These windows were a lot heavier than the old ones, as they were also sliders and you really could feel the difference in the weight

But they remained fog and ice free, even at -40. The entire suite felt much warmer in winter too. Not to mention much quieter - couldn't hear the street below

In a moderate climate, I'd pick tri-panes just to have a quieter house. In a severe climate (Most of Canada is "severe"), tri-panes are a no brainer