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1/25/10

Passive Solar Prefab House Kit: Touching on ERV / HRV, Fireplaces And Dessicant Wheels

If you're wondering, we have no intention of having our own passive solar prefab house kit certified. That's not to say we're not mentally aiming for passive house / similarly efficient standards, so a lot of passive house information I link to regarding our off grid house kit systems is because it is designed for highly insulated, tight homes like our own prefab house kits.

You know our house kits are energy efficient, being built with SIPs (structural insulated panels), passive solar, and designed by LEED accredited architects. That is not to dissuade you from certifying your own house kit- there is much value in how far you can take this bare-boned house kit architecture- pushing it as far as you want in energy efficiency and off grid / net zero energy systems, with the help of an accredited certifier.


A tight, energy efficient passive solar house kit built with SIPs also means you are going to need a way to mechanically exchange air, preferably without losing / gaining temperature from the outside, as well as ensuring moisture does not sit within the house kit.

Talk to your contractor about what works for your area and for your own needs, but here are some links I found educational:


Any-hoo, we are currently trying to figure out if the mid-century fireplace is worth the effort / expense; whether it is worth adversely affecting the house kit tightness to integrate into our prefab house kit when we could spend that money towards systems. 

We originally spec'd the systems plan to not have a fire place- coupled with radiant heat, an efficient stove would easily overheat the net zero energy house kitBut when it got down to eleven degrees and we were still without our off grid systems installed, I went a little crazy.  Handsome Husband knew the disadvantages the entire time; I did too, intellectually; but try explaining that to the frantic-mom-inside-of-me-trying-to-resolve-warmth-immediately.

Regardless, the coolio modern fire place will be put to use, even if as just an outdoor feature... but that doesn't help us when we haven't installed systems and need heat immediately... it's a shame if we can't incorporate it, now that it's there.

From Handsome Husband:

"We started with our desire to be warm, not yet having purchased and hooked up our systems. Getting the (admittedly cool) fireplace led to the realization that a ERV would need to go hand-in-hand with such an installation (or anything), coupled with the need for a fireplace / stove in such an efficient house to prevent back draft. Many people now realize that burning a fire in a fireplace in a traditional home has the following effect: the flu sucks air out of your home in a big time because, boy, does heat rise and air gets shot out of your flu.


Well, that creates negative pressure in your house - air is sucked out of the house. In a conventional home you get new air sucked in through the cracks in your house to maintain balance of pressure with the outside. In a home built with SIPs the envelope is much more uniform and easy to seal- you do that, of course, and end up with a home that doesn't have cracks to suck in enough air to balance the loss of air through the flue. What happens next apparently is that the negative pressure in the house exceeds the power of the air rushing through the flue. Bad news because now the smoke from your fire no longer wants to go up the flue but instead becomes the means to de-pressurize the house, compensating for the previous loss of pressure.

What to do?

Sounds like one wants to prevent de-pressurization. This occurs when air is sucked out of the house - something we don't want anyway because we just HEATED that air. So you decouple the flue from the house by giving it its own snorkel - sucking air for combustion in from the OUTSIDE through a tube running from an outside wall to the inlet on the fireplace.


This works great for SEALED fireplaces or wood stoves or, of course, pellet stoves. In our case we have the mod version of a chiminea and we have to see whether we can a) attach an external air supply to it and b) seal the fire place by replacing the screen with a sealed cover.

Fall back is to use it seasonally by swapping it with a sealed wood or pellet stove with external air supply."

In the meantime, here are some video updates on the modern prefab passive solar green home:

Still sorting VMI floorboards to reuse in the passive solar house kit...

Note to energy enthusiasts: He also discovered there was a pipe that had not been correctly sealed during the energy audit... which certainly contributed to temperature drop / leakage... that is now corrected!

Net Zero Energy Passive Solar House Kit Update

...An unexpected visitor to the net zero energy prefab modern house kit:
(Dude, don't eat mah steps!)

Handsome Husband Encounters His First Hog


Now, now. I know we've been persnickety as of late, but don't think we're soured and nasty over all the recent heating hullabaloo...
Despite the prefab zero energy house kit setbacks, we keep on tha' sunny side! (Right June?)

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