Cohousing-L Mailing List: RE:[C-L]_ancillary heating questions

[Chris Miller (cmmelas]

Radiant floors seem to be a desirable heating method for cohousers - and for
good reason.  As a mechanical engineer/energy analyst, I design between 1-2
radiant system per week and I believe it is the preferred heating method for
multi-family dwellings.

I'd like to address some of the reoccurring radiant issues I've seen lately.

Effectiveness:
-  Radiant heat is most effective if there is little or no insulation above
the radiating surface (i.e. - the slab).  The best option therefore is
exposed, stained concrete.  Followed by tile, then vinyl, then wood, then
throw rugs, then wall-to-wall carpet.  Radiant heat can nearly always work;
even below carpet it is effective - especially if that added insulation
effect of carpet is mitigated by tighter tube spacing, higher water flow and
possibly (worst case, due to more cost) higher water temperatures in select
zones.  Also, most of the insulating properties of carpet is from the pad -
that can be reduced by a factor of four by purchasing a carpet pad designed
for radiant use.  A second note on floor coverings should be that radiant
works very well under wood floors - don't let your contractor talk you out
of it if you really want wood.  It just takes some thought on how you intend
to install it (nailed directly to wood sleepers embedded in the
concrete/gypcrete or on a floating floor system - which is just a couple
sheets of plywood on top of the slab), also be careful to keep the slab
surface from exceeding 85 degrees (which, if you're serious about this often
neglected point, means slab temperature sensors), and let the wood acclimate
in the house before it is installed for as long as possible (a couple weeks
is typical).

Energy Efficiency:
-  In most applications, radiant heating is as efficient as the heat source
is.  If you purchase a 94% efficient boiler, you will have a very efficient
system (especially if you keep the hot water piping located outdoors to a
minimum.)  You don't have the same duct loss to attic/crawlspaces that is
associated with forced air (between 10-30% heat loss in most new
construction); all the heat in a radiant system goes to the conditioned
space (I'm assuming a properly insulated structure.)  But, that said, you
should consider there to be no energy benefit by going to a radiant system
(there often is some benefit, but not enough to offset the additional cost.)
That is unless you tie in solar to the floor heating system.  Radiant
heating is the single best way to take advantage of solar directly into a
mechanical system (I'm not talking about passive solar - that should be done
anyway.)  Tying in solar to a radiant system is expensive, but the costs
come way down if you do a central mechanical system for each multiplex
building.

Comfort:
-  This is mostly why folks use radiant heating.  It is far and away the
most comfortable means of heating - I have never had a client regret
installing radiant heating, but have had several regret cutting it from the
project due to budget issues.  This is what sells radiant heating.

One more thing, for those folks talking about doing radiant floors on the
downstairs and baseboards upstairs, I'd advise against that.  The common
perception is that baseboard upstairs is more cost effective, but the last
3-4 jobs I've been involved with have been more expensive with the
baseboards (I only know this because my clients requested the installer to
bid it both ways, and the baseboard option has been higher each time).  This
is partially due to the baseboards I spec (which are not the cheapest ones -
but they are much better looking and put out more heat per linear distance),
but mostly because it costs extra for the plumbing (considerably extra), and
you have to go to a two temperature system (the floor calls for 120 degrees
usually, the baseboards 180 degrees) - which does cost more, but mostly is
adds a layer of complexity you don't want to add if you can avoid it.  If
your reason for going to baseboards upstairs are because your contractor
said to do it, then get a better installer.  If you want to go to baseboards
then do the whole house that way - that really is cheaper then radiant
floors (if you do any floor heating you have to throw a lot of money into it
to start - adding the upstairs doesn't add much cost proportionally.)

Hope this helps with your radiant questions.
Chris Miller
Nevada City Cohousing

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