in pursuit of energy efficient minimalism

fire… in a passivhaus?

It’s a question we’ve had a few times… ‘Can I have a fireplace in a Passivhaus?’ While not strictly verboten, fireplaces and PHs generally don’t go well together. Wood burning fireplaces are out. Just right out, you’ll never hit the blower door test, it would invalidate HRV effectiveness, cause drafts, incur significant heat losses. Plus, they aren’t so great for IAQ. In winter here in the NW, we tend to have some horrendous air quality (burn bans aren’t infrequent!)

Direct-vent gas stoves that are completely self contained could be possible, but the average unit has an output that is 5-10x greater than the peak heat load of a PH – who wants to bake in their house?!?

The fundamental allure of flame, however, is undeniable. For us, the fun part is finding viable alternatives, so here are a few we rather like…

 

Bio ethanol

A decent option for a PH, as no chimney is required. The byproducts of combustion are CO2 and steam/water. The heat output is generally low but can be adequate for a Passivhaus, and there are some snazzy modernist models, perfect for your man cave or living room… One of the more minimal units we like is produced by vauni. Although I think by law, if you put this in your house, a Jacobsen egg chair is required.

 

Pellet boilers

I have to say up front, I find this the ‘sexiest’ option. These can be found in a number of PH projects, though they tend to be utilized more for DHW. There were some interesting units in Hannover, and one of these vendors was Wodtke, which has a rather nice unit compatible for a Passivhaus. Of all the units I’ve seen, they’ve also got some of the best aesthetics. The majority of heat put out by the boiler is sent to a DHW storage tank, with a small portion going towards space heating – best of both worlds for a PH.

Now there are some planning issues – sourcing pellets in the US ain’t as easy as Europe – though New England does have a decent infrastructure in place. The pellet storage is typically self-contained, there are systems that store from a few days worth of pellets to nearly a year. Some of the systems have separate hoppers which can be quite large (I’ve seen systems incorporated both in and out of the thermal envelope). This adds envelope penetrations, which may just need some extra effort to be sealed and insulated…

What I like about these units is the heat output is low enough that overheating is low risk. The efficiency of the systems is relatively high. The pellets are comprised of compressed saw dust and wood shavings – so in essence it’s a recycled waste product – and the ash byproduct could be utilized in a garden as fertilizer, depending on type of wood sourced. The bonus with the pellet boiler is that your primary demand number goes down considerably, especially compared to an all-electric system. Many in the PH community, however, would argue that the biomass source factor (0.2) calculated by GEMIS is entirely too low.

 

Thinking outside the [thermal] box…

If you really want the option of a wood burning fireplace paired with a Passivhaus, the smartest location may be placing it outside the thermal envelope. Two of our favorite solutions: a 3 season porch or a fire pit. Given our minimalist tendencies, the firepit is a must – especially here in the Northwest where summer evenings can still be really cool. It also provides that natural desire to congregate around a fire. Mmmmm. Fire pit!

Throw a dinner party w/ a few candles…

I think this one is self explanatory… A few friends, good food, and some scotch – all the warmth your Passivhaus requires.

Some hae meat and canna eat, And some would eat that want it
But we hae meat and we can eat, Sae let the Lord be thankit.

So those are a few of our ideas. We’d love to hear your thoughts in the comments. Cheers!

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