Notes on a hydronic radiant floor JuicyMaters

Notes on a hydronic radiant floor JuicyMaters

Notes on a hydronic radiant floor

Aug 27 2010

Wednesday, February 24, 2010

Well, I’ve been in my yurt for about 5 months now…

I know, I know…the construction articles stop at platform construction.  I’m gonna finish ‘em soon.  There are about 4 more construction articles to go and they are all already in the pipeline…be patient.

Anyway…after 5 months of yurt living. including the coldest part of the winter, I’ve got some observations on my radiant heat floor…and they apply to any radiant floor on a crawlspace, not just a yurt.

This radiant floor thing was new to me when I started my yurt.  I had done a lot of research on all the house systems, as this is the house I’ll live out my life in and I wanted to be happy with everything so I checked all my ideas very well before starting.

My criteria for the systems were:

They must be initially economical to purchase and install…economical, not cheap.  There IS a difference.

They must be economical to operate.  I live on a very limited income and monthly expenses must be kept to a minimum.

They must be durable.  Both for money and for convenience reasons I wanted systems that were “build and forget”, except for maintenance, as much as possible.

They must be efficient.  I don’t care how inexpensive to install and operate a system is, if it doesn’t do the job it costs way too much.

Based on those criteria I chose radiant floor heat as my heating system, despite the fact that I had never, to my knowledge, even been in a building with radiant floor heat, much less had to live with it.

I’ve gotta admit…if I had written this article in mid-December I would have been talking about what a poor heating choice I had made.  The first of the really cold (for here) weather had begun and two things were happening regarding heat, and both were bad.

First, I was COLD!  Nights in the upper 20’s outside temperature were giving me inside temps of about 53-55 degrees when I got up in the morning…not freezing certainly, but very uncomfortable.

Second, it was costing me a fortune in propane to get what little heat I had.  I was going through 125-150 gallons of propane a month to heat the 700 square foot yurt, run a gas dryer twice a week, and cook for just me.

I was very disappointed…and wondering how I was going to afford to heat the place when temps dropped more.

I went back through my research on radiant floors, and took another look at my installation to see what might be wrong, and discovered a fatal flaw in my approach.

I had acted like my radiant floor was a heater, not a heating system!

I tend to be a bit lazy when I can get away with it, and my laziness had caused me to only do half a job.

The radiant floor itself was properly installed…but the floor was a heater, not a heating system.

Because I had mostly finished the yurt in mid-September, I drug my feet on the final work…including turning the floor heater into a radiant floor heating system.  The floor joists were not insulated, the floor joists were still open to the elements, and the yurt had no underpinning, standing on its posts like a stilt house on some Pacific island beach.

Well, DOH.   Pacific island beaches don’t have temps in the teens and 20’s!

The pex tubing embedded in my sub-floor, along with the water heater, makes my floor a heater.  The following three additional items make my floor an efficient heating system…finally.

1.)   Insulate the floor joists.  Fortunately, when I ran the plumbing and electrical for the yurt, I had consistently drilled through the joists high up so the heat from the floor would keep the plumbing from freezing in cold weather.  This left plenty of room for R-30 bat insulation between the joists and under the plumbing and electrical, keeping them even warmer.  As an added benefit, this will SLIGHTLY lower your hot water costs.  Since the cold water lines are kept so warm, it takes less hot water to temper the water for a nice, hot shower.

2.)  Cover the bottom of your floor system with an airproof material stretched and stapled to the bottom of the floor joists.  I think Tyvek is probably the best material to use but any air-proof material will do the trick, even roofing tar paper.  Be sure you overlap the edges of the material and attach it to the joists every 8 inches or so to avoid air infiltration through the gaps.  This will help insulate your floor two ways…it will prevent the wind from carrying away heat from little nooks and crannies around your bat insulation and joists, and it will act as a barrier to critters that like to burrow into bat insulation, like rodents, to make their homes.

3.)  Underpin/skirt your foundation as a further cold air barrier.  Depending on how you plan to finish the house below floor level, here are two suggested methods.

If, like me, you intend to build a walkway all the way around your yurt, consider having the good looking finished underpinning at the outer edge of the walkway rather than at the outer floor edge (I plan to face-rock the outside of the walkway after I build it) and wrap the outside of the yurt edge with Tyvek stapled to the legs.  If you are going to build a walkway like I am there is no need to spend money on underpinning looks.  Then, after building the walkway, put whatever surface on the walkway underpinning you want so it looks good…as I said, I’m going to face-rock mine.

If you aren’t going to build a walkway, or if the walkway is going to be open underneath, then still wrap the yurt underpinning in Tyvek for an almost windproof barrier and put your finish covering over the Tyvek.

Learn from my mistakes.  Make your radiant floor an efficient radiant floor heating system, not an inefficient, and expensive to operate, radiant floor heater.

Editor’s note:

All posts on JuicyMaters are meant to be discussions, not lectures.  Please use the comment box at the bottom of each post for questions and comments, or to suggest another way to do something related to that post.  My way of doing something is A way, not THE way.  Suggestions are welcome.

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