Desperate for advice on replacing dead 255K BTU furnace in 3200 sq foot house

Solar mass is just plain cheating though...LOL

Reply to
Solar Flare
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Iain> 332k BTU on those February days... Nick> 90K Btu/h in full sun.

Iain> lose 50k BTU through the windows. Nick> 5.4K Btu/h.

We're in agreement here, Nick.

Iain>he'll need to vent over 1000 cfm at 80F (from outside 55F).

I calculated 1500 cfm for venting the incoming radiation as heat at 80F from 55F, averaged across the few hours of insolation. But I figured he'd lose some through the rest of the house. Your number, below, is at the peak heating rate and assumes no other loss. Both of us, incorrectly, assume that the full area of the window is insolated.

Nick> cfm = (90K-5.4K)/(80-55) = 3384, approximately.

"Cancelling" air's 0.02 BTU/ft^3-F and 60 minutes/hour, so nobody can follow your units.

Iain>...and many, many tons of water.

Nick> With enough insulation, it wouldn't need any water, nor windows.

And *right here* is where you miss your opportunity to help a lot of people.

The windows make this house. The interior was deliberately opened up so that most rooms could see the incredible views. If the house had no windows, your penpal would have bought a different house.

As you keep pointing out with your cube analysis, we could live comfortably on far less energy. In fact, people all over the earth do just that every day.

But you advocate going farther down the path of form following function than most people care to. Ultimately, that gets you ignored by most folks, and defeats any aspirations you might have to lowering overall consumption. Windows are not put in houses primarily to gather heat. They are there to make us happy.

Engineering analysis that says not to put in the windows is not useful. To be useful, analysis must minimize energy consumption while constrained to other, more important goals, like having a nice view or cheery lighting most mornings, or having the house look a certain way.

A house in a 4000 degree-day environment can get through cold sunny days just fine with solar heating alone so long as it can store the heat. If the heat will be stored in the habitable envelope, the water will only swing about 10 F before things get uncomfortable. We can fairly easily guess the volume and surface area of this storage, and with R1 windows it is essentially a foot-thick sheet of water the size of the windows. Modern glassy houses thus need to contain very large amounts of water, or even larger amounts of something else to store their heat. This isn't usually practical in a retrofit.

Reply to
Iain McClatchie

Windows are bad. They are expensive, and installing them is expensive, and the framing leaks heat, and they can leak heat and air and water and sometimes bugs and burglars. Let's replace windows with outdoor cameras and computer projectors or flat screen TVs, with fluorescent lights and doors or push-out panels for fire escapes.

For drama, you might put windows or a single layer of polycarbonate glazing on an isolated low-mass sunspace with an enclosed solar staircase roof and a dark mesh curtain near the windows.

A thin layer of 120 F water goes in a lay-flat poly film duct above a low-e ceiling surface in the living space heated by hot air from a sunspace during the day. At night, the sunspace gets cold and the airflow stops and a slow ceiling fan with a room temp thermostat and an occupancy sensor warms room air as needed.

Nick

Reply to
nicksanspam

Perhaps this is so, but at some point you have to say "screw efficiency" and look out a real window at real life and allow sunshine into the room.

Reply to
Edwin Pawlowski

Other wise S.A.D.S. sets in and then you become a Usenet addict

Reply to
Solar Flare

Nick> Let's replace windows with outdoor cameras and computer Nick> projectors or flat screen TVs, with fluorescent lights and Nick> doors or push-out panels for fire escapes.

So you see how untenable this position is.

I was thinking a little more about the OP's issues heating his house. It sounds like he's on a south-facing slope. Some of the slopes in that area are steep enough that his lower floor may be off the ground on piers which are illuminated by the sun. Alternatively, there is

2000 ft^2 of upper floor not over lower floor, which may also be on sunlit piers.

In either case, he might be able to build one of your solar closets down among his sunlit piers, then use air blown through that to heat the house at night. It would make the house much more usable, increase resale value, and aesthetic issues with DIY-built stuff would be less important since it's out of (his) sight. Also, in that neighborhood a homebuilt solar closet may not generate adverse comments from the neighbors.

If he can pick up 600 BTU/ft^2/day in February, store it through much of the night, fix the worst of his air leaks, and add some attic insulation, he might get half his heating done with 400 ft^2 of solar aperture and 500 gallons swinging between 90 F and 140 F. That'll save a bundle on the replacement furnace and the bills from same. Depending on the house configuration, there may be 40 lateral feet of sunlit piers down there, so there is some chance of fitting significant solar aperture. On steep hillsides, angling the solar closet glazing slightly (15 degrees) face-up from simply vertical can greatly increase the vertical extent of the glazing without chewing up a lot of real estate. He might implement a 10 or even 20 foot tall face for the collector.

If I were going to do any such thing: - I'd get a contractor to build the footing and concrete pad under the house for the heat store. Someone used to doing foundation work, who won't screw up the existing footings. Have them drill a pier to bedrock if necessary. - I'd go big on the heat store. 1000 gallons if you can manage it. - Use 55-gallon (or 40-gallon if you can get them) used plastic barrels to store the water. - Build the glazing as tall as possibly practical. It doesn't weigh very much and often people don't use steep real estate below their house. - Heat the water directly rather than use an air heater to transfer heat to the water. The EPDM mats seem like a nice solution, but you'll not like the $5/ft^2 price.

Reply to
Iain McClatchie

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