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Learning, Sharing, and Teaching => Ask a Mustachian => Topic started by: bbates on February 17, 2014, 09:00:21 AM

Title: Possibly buying a house! Need advice on passive solar heat
Post by: bbates on February 17, 2014, 09:00:21 AM
Hey guys, I'm brand new here (to the forum) and this is my first post.

My wife and I are looking a buying a certain house and I'm wondering about passive solar heat.  I'm relatively new to the concept so I can't quite wrap my head around it all yet.  We've lived in an apartment for 6 months that stays at 70 degrees (F) inside with no heat running while it's -15 outside.  It's really amazing, but I've become quite spoiled to the low heating bills.  I don't want my electricity bills to skyrocket (although I'm sure they'll go up some) just because I bought a crappy house.  Here are some stats of the house, any advice?  Anything stand out to you?

<1,400 sq ft
2 story
Brick
Corner lot, full brick wall gets southern exposure.  No trees, no houses, just sky.
A few decently sized windows on the southern wall that shine into living room and kitchen.
Forced air heat
No A/C (may get this installed if we can't take the summer and to add value to home)
Dry, Colorado climate
When we went for the showing, it was about 60 degrees(F) outside, but probably 10 degrees cooler inside.  Is that a good or bad sign on insulation?

I'm sure I'm forgetting something else, but on first glance, what does this look like to you?
Title: Re: Possibly buying a house! Need advice on passive solar heat
Post by: FrugalSpendthrift on February 17, 2014, 09:28:08 AM
Those stats don't really tell you if the house is efficient or not.  Does it have newer windows and doors?  A house that has a really good air seal will typically have a heat recovery ventilator, to make sure the house gets enough fresh air.  Generally it is good to have trees on the east and west sides, but not the south.  Window overhangs can block the high summer sun, but allow the low winter sun, if they are sized properly.

Ask to see their previous energy bill.
Title: Re: Possibly buying a house! Need advice on passive solar heat
Post by: Greg on February 17, 2014, 09:28:40 AM
Welcome!

The brick wall outside probably won't help you out in terms of passive solar heating.  It's likely got an air space behind it that will vent most of it's heat gain before contributing to the interior heat.

Most important things about a home like that are likely to be insulation and air sealing to reduce unwanted air flow and heat loss.
Title: Re: Possibly buying a house! Need advice on passive solar heat
Post by: Abe on February 17, 2014, 10:11:07 AM
Are the windows double pane or single? Double pane windows provide more insulation. What is the flooring material in the room with southern exposure? They provide the thermal sink needed for stable indoor temperature, and preferably are made of stone or concrete. Feel the floor with your hands, if it is cold in the afternoon, it is probably not a sufficient heat sink.

Wall and roof insulation is the most important thing, but can be hard to assess. I would feel the walls when the interior is heated above the ambient temperature. If there is a lot of cold spots near the ceiling, windows, doors or corners, that suggests a poor insulation job. With brick exterior, the only way to fix it is with blown-in insulation (much easier if you have access to an unfinished attic) or taking down drywall and adding batting (expensive and time-consuming). For roof insulation, if there is attic access it is straight-forward to assess and add more as needed. If you are very serious about passive solar, I would pass on the house if either of these are poorly insulated as it is difficult to remedy in an cost-efficient manner.

The best way to objectively assess would be finding information on the previous years' heating bills and ask the owners how warm they kept the place. If the owners are unwilling to provide that, move on.

If you do decide to purchase and live there for a long time, I would recommend planting trees on the sides other than south. Consider fast-growing trees that will get to 10 feet in a few years.

With regards to the heating bill, the house is small enough to consider a wood pellet stove for heating the areas you will spend the most time. Using stone for the surround is a good way to add a thermal sink to the living area, especially if it faces the southern windows. The cost may significantly depend on local building codes. 

Good luck! Check out your local library for more books on passive solar heating!
Title: Re: Possibly buying a house! Need advice on passive solar heat
Post by: phred on February 17, 2014, 02:01:12 PM
Can't tell.  To answer your questions you really need to spring for an energy audit.  Think of it as paying for a super home inspection.  Ensure that the auditor is familiar with both solar siting & solar tempering

As to the trees: you want widely spread deciduous trees on the south side to shade the roof.  Widely spaced so that the lower winter sun can come in after the leaves drop.  For the west side - the evening sun is lower - a dense hedge or a long fence/trellis covered with vines with awnings on the second floor windows.  Trees don't work as well on the west because the leaf mass is up & so doesn't shade the first story wall..  The east side - nothing as the morning sun will make the house brighter saving on lights.  The north side is generally evergreens to act as a winter windbreak; these should also curve around to the northwest as well.  Exact placements will also depend on the typical wind patterns at your house; different directions at different parts of the year.

Beware of fast growing trees such as the Empress.  The wood is weak and the limbs can break & fall without warning.  These trees really like to plug your sewer system while searching out water.

If the southerly rooms are shallow, the winter sun may be hitting the wall instead of the floor,  A plaster wall will be the thermal mass.  For the proper spacing of the trees you may need to plant some of them in the neighbors' yards - with their permission of course.