Need Advice for Small Addition, Hydronic vs Electric floor heat.

jschapht

Hi. As a serious DIY'er and the owner of a big old house with a converted gravity system, I have been an avid reader of this board for years, but this is my first post.

I'm putting on a small addition (~200 sqft) and the foundation will be slab on grade. I am interested in doing an in-slab hydronic radiant floor for the addition. I am proposing to do this myself (to save costs, I am already spending too much on this addition), but my general contractor is pushing an electric system. He is not familiar with in-slab hydronic radiant and much more comfortable with electric floor warmers. He is concerned with possible liability if something goes wrong with the hydronic install. Also, if we go with the electric, he will probably do that work.

Should I insist on hydronic, or go with the electric system?

More background:

Existing space that we are adding to is heated with a large cast iron radiator. We have a basement underneath most of the space, where my eventual plan is to run pex between the joists with heat transfer plates. A small portion of the space has an inaccessible crawl space underneath. If we can somehow gain access (knock some blocks out of the foundation) we could put tubing under there as well, otherwise it wont get heated. We have nice tile floors in the existing space that we really don't want to disturb.

I am pretty confident in my abilities. I have done a lot of other work on my system already. I added a variable speed injection pump with outdoor reset (with primary secondary piping as well) and also replaced the old compression tank with a new diaphragm tank. I have read a couple of Dan's books, and if you have made it this far I will also let you know that I am a professional mechanical engineer, with a background in construction. I don't do this sort of stuff for a living, but I design other sorts of piping systems, so am pretty comfortable with this sort of stuff.

We live in Philadelphia area. It gets pretty cold sometimes.

Thanks.

j a_2

Interesting, we as plumbing /heating contractors often design/engineer our own systems, it’s almost a must out here...I like the fact that your doing your own, as skilled labor is becoming increasingly difficult to find...Besides it’s always good to see the the obstacles we out here put up with, that the nice little computer programs don’t see...you will become a creative engineer...
All that said I much prefer radiant over electric, just because...I am sure you will have fun running the numbers on temps and flow rates and all that fun stuff..you might even enjoy the manual part,the actual installation...But the real enjoyment will come when your all done and the first time you get to see people enjoy something they can’t even see...best of luck

Dave H_2

Sometimes the biggest difference between electric and hydronic radiant is the output you can achieve. Alot of the electric systems are designed for floor warming and not much else. Depending upon the BTU's/sq you may not be able to heat the space to design conditions.
With hydronic, you can almost always heat the space, you can adjust tube spacing, water temperature.....to get the heat you need. Since you already have hydronics in the house, its a no-brainer.
I wouldn't worry about what could go wrong from the general as long as the math has been done. You can never, ever be wrong if you do the math.

Dave H.

KC_Jones

Since you have hydronic already I would probably stick with that. BUT.
If you contractor isn't comfortable with it I wouldn't have him do any of the work on it. Literally none of the work. You should get someone that knows what they are doing. The details matter here and can be the difference between shorts and t-shirts in winter and icicles hanging off your nose....seriously. Also if he is even willing to

If you are comfortable doing it yourself then go for it, plenty of smart people on this board that can help and answer your questions.

my $0.02

Zman

I would never do electric if hydronic is a viable option. Electric has a lower output, will not last as long and in most markets it is more expensive to run.
From the sounds of it, you could run 1 or 2 loops in the slab and tie it in at the boiler room with a small mixing setup. Don't forget a minimum of 2" ridged under and at the edge of the slabs.

Rich_49

Here is some simple math for you .

Natural gas . therm = 100,000 BTUh . 1.00 + - , area specific

Electric . KWh = 3414 BTUh . .15 per , again area specific

Let's review , 100,000 / 3414 = 29.29

29.29 x .15 = 4.39

1 x 1.00 = 1.00


If your room had a load of 5000 BTUh @ design and those conditions lasted a full 24 hour day it might cost you , the end user 1.85 plus about a dollars worth of electric ( pumping) to heat that room using a hydronic system . That same room under the same conditions using electric source would use 35.04 KWh or 5.25 for that day . Just another but more powerful view . Your rates may vary from my examples