underfloor question

ChrisK_2

Great. I was planning on using the Triangle Tube Prestige. This my first dive into the radiant world and it good to know that that I'm not out in left field.

Thanks again

ChrisK_2

underfloor question

I'm planning the underfloor radiant system for my renovation in Seattle. The main level is ~900 sqft and consist basically of one large open space except for a bathroom. I was thinking a single zone for it. The subfloor is 3/4" shiplap with 1/2 plywood screwed on top of that, then a finish floor 1/2" engineered wood flooring. This is all over heated space.

I'm planning on using 1/2" pex with extruded plates doubled up per joist bay (joists 16" OC) with a mod/con boiler.

I've been using the slatfin heat loss calculator with 68 for indoor temp and 24 for outdoor. It came up with 23 BTU/sqft and that I will need a 140F supply temp.

Do these figures seem reasonably correct? Is 1 3/4" of wood (plus the floating floor underlayment) too much r-value for an underfloor application? Is this high supply temp going to cause problems and/or just plain silly?

Thanks for your help.

Mark Custis

Now you are talking

Remember heat goes to cold. I like two runs per 16" OC joist bays if at all possible. Plates are the way to go with pexA. Then insulation. I always install at least a manual three way mixing valve.

I think 140*F maybe two hot. Use the mixing valve to drop the water temp. 300 ft is the longest we run in 1/2" pexA and the increased cost of a good manifold with flow meters, thermometers and acctuators is well worth the expense.

kpc_45

if it is ...

a mod con you don't need the mix valve.Ste it to run at the design temp as the max temp. the boiler will do the rest.
As to the heatloss the Slant/fin program will give you a ballpark idea but it is not a radiant heat program. you really should get a professional heatloss done.

ChrisK_2

I used the City of Seattle heating equipment sizing form (excel sheet, link below) to verify the heat loss figures. They came out to within 350 btu/hr of the slant/fin loss values.

Are you saying that the radiant design part of the slant/fin program (supply/floor temp, floor R-values) are only ballpark?

City of Seattle heating equipment sizing form excel sheet:
http://www.seattle.gov/DPD/static/HeatingEquipmentSizingForm2006wsec_LatestReleased_HeatingSizingForm2006.xls

ChrisK_2

Thanks.

When you say 140 maybe too hot do you mean that the figure does not seem correct (22 btu/hr, 1 3/4 thick floor, 2 runs of extruded plate per 16OC joist bay) or that 140 is just too high of a supply temp to run in an underfloor application?

kpc_45

you must have...

a more updated version than I... mine does baseboard only.

PLUMBARIS

To hot

From past experiance 140 is not to hot in a staple-up application.

ChrisK_2

I have the one from http://slantfin.com/heat-loss-software.html

The radiant design stuff is pretty hidden though. You have to double click on "Radiant tubing - ft selected" field and a new window will pop up where you can enter the floor build-up/R-value, the heated floor area, max surface temp. It will calculate the supply temp and tell you if you need any auxiliary heating.

Mark Custis

I am in Cleveland OH

We have lots of radiant stuff done in this market.

I run lots of pipe and low temps.

tim smith

Chris, I don't see a problem with that max temp with plates and

engineered floor product, you may be able to go a little lower on temp in real world. We have done quite a few this way in Seattle as this is where we reside. Sounds like a nice project for you. Triangle tube prestige mod/con is what we like to use in this application. Tim