Tiny Hydronic Radiant -Can it be done?
Hello all, new to the forum, love it!!
I recently remodeled a bathroom in my 1908 house and am now thinking of putting in hydronic radiant from below the bathroom floor, between joists.
Problem is, the bathroom is small (80 SF) and I can see the system not cooling enough to work with my exisitng gas boiler that heats the rest of the house. What I mean is that when that boiler heats the rest of the house (currently only one zone), it is heating many many gallons of water (60-80?) whereas if I had a seperate hydronic radiant zone for the bath, it would only contain a few gallons of water–the gas boiler, as far as I can see, would heat up quickly, circulating only those few gallons of water, then shutoff, cycling quite often which, from my understanding, is not great for such a unit…
Anyone have any thoughts?
Would love anyone’s input, especially if you have experience with small hydronic radiant zones!
Thanks,
davetz
Replies
your boiler will be busy heating the rest of the house. the bathroom is already at temperature thanks to the radiators in the rest of the house. the under floor heat for this bath will be a nice foot warmer. you need not worry about your boiler short cycling if the new loop is set up properly.
my biggest concern would be what it is going to cost to put another circulating loop on your existing boiler. sounds like the rest of the radiators are running at full temperature. your new radiant can't do that, the water must be mixed with cooled water to lower the temps.
if you put a tile floor in, this would have been a lot less expensive to run an electric cable system prior to tile install.
carpenter in transition
Thanks for the tip Tim. It is a tile floor and indeed I know it would have been easier and cheaper to install electric before the tiles! Alas.. live and learn... How would one pipr the system to cool water properly so that a mixing valve would be effective? Since the loop would be so small, it seems the return water would be almost as hot as the supply water, ie. not much heat loss in such a small zone, so where does the cooler water for the mix valve come from?
Thanks again,
dave
A mixing valve will only let the floor "see" a user set amount of cooler water that is coming from the floor. You could crank it down so that youre only sipping the hot supply water, and using (most of the time)water thats already been through the floor. So that's no problem.
You could put the pump and valve upstairs if you can hide it behind an access panel, or put them in the boiler room.
Here's one of several ways of piping it.
View ImageRBean
http://www.healthyheating.com
http://www.healthyheating.com/blog
Thanks for the tips, all. I understand exactly what you're saying about the mising valves and all that.. Just that it seems whenever the water in the loop gets too cool--and I imagine that would happen fairly fast--it will call for heat from the funace and that means the furnace would cycle often, no? Or am I reading it wrong that furance cycling is a bad thing? Also, anyone know where I can get a good mixing valve online? Honeywell seems to make a good quality product.
Thanks again,
dave
A simpler approach would be a pair of monoflow tees that would tap a small amount of heat from the main loop, and send it through the loop under the bathroom floor. All you're trying to do is warm the floor tiles, so why bother with the hassles and expense of a separate zone?
I would think the main reason would be 190 deg water hitting the floor....would get way too hot to walk on.
I know what youre saying though. There are guys that do just thermostatic radiator valves for radiant floors, and use the system circulator to pump through the floor (providing the bath isnt huge). Doesnt get any simpler. But, no ability to zone.
"I would think the main reason would be 190 deg water hitting the floor....would get way too hot to walk on."That's certainly true if the tubes are embedded in the floor. I was thinking of the radiators that sit in the space between floor joists and don't actually contact anything. A small flow of 190F water there wwould probably work well for the limited heating needed.
How old (or what kind of shape) is the current heating plant? This would influence my decision if I were in your shoes. RBean
web: http://www.healthyheating.com
blog: http://wonderfulwombs.typepad.com
You need to avoid micro-zoning. Several ways to go about it.
Check this out from the oracle of hydronics:
http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,62497,00.html
csnow,
Are you going to RadFestEast?
John "the oracle" will be there in person.
http://www.rpa-info.com/RadFestEast/seminars.htm
Cheers,
RBean
web: http://www.healthyheating.com
blog: http://wonderfulwombs.typepad.com
Robert,
I should have said the 'other' oracle of hydronics.
I have been to a couple of Holohan events, but as only a hydronics hobbyist, they have to be very local and relatively inexpensive to justify attendence.
BTW, thanks for taking the time to help folks out by posting on this board. We are lucky to get such expertise here.
It would be great to hear about your hobby! (me thinks its beyond tinkering!)
Both Dan and John have contributed so much to the industry.<!----><!---->
John with his degree in engineering and Dan with his degree in sociology bring the technical and human factors together so that it makes sense to everyone from - well – engineers to consumers. Grin.<!---->
I’m just here to bring the past into the present so we can move into the future.
Thanks for your comments...always look forward to reading yours.RBean
web: http://www.healthyheating.com
blog: http://wonderfulwombs.typepad.com
Have you considered using an electric radiant heat mat over thinset and under tile? You would have to rip up the floor, but now that we did it, it is OH so worth it. and we are able to use ours as the sole heat source for our bathroom which is about 80 sqft.... we did a nu heat system.