Grafting radiant to hot water baseboard

OneHungLow

Hi, I am in the middle of an addition (12x16 added to kitchen). My original plans were for adding 22 ft of fin tube baseboard to handle the heat load of the addition and kitchen. I am in the revision process now, and am planning to heat with 1/2" pex and heat transfer plates spaced 8". I have designed this several different ways and like the primary secondary for the control on return water temp and pump isolation. My problem appears when I calculate the heat load and available floor area I have to work with in either room. The galley kitchen is 8x15, requiring 2089 btu/hr and due to cabinets/fridge has 52 s.f of area to work with. That's 41.8 btus per ft....and the addition needs 31 btus per ft. Is this unrealistic? I was told that the kitchen could have pex under the cabinets with out heat transfer plates as this would add to the volume and the plated areas would draw the heat to them on off cycle times. Any advice is appreciated. Thanks Bill

CMadatMe

Yup

If the avaible sqft of floor doesn't allow you enough tubing then yes it's realistic. I just ran the numbers you provided for that kitchen and I get:



Floor Surface Temp of 88 degrees with a floor that has an output of 40.3 btus sqft. You also need 193 degree water to do this. I used a floor R-value of 1.58 figured it for the subfloor and tile.. Wouldn't attempt it though....Your going to need some supplemental heat.



I have a suggestion that will work real well with the radiant. How about some radiant panel baseboard under the kicks of the cabinets to bring down the floor need?

You can look at them at www.hydronicalternatives.com

I also wouldn't be running 1/2 pex and 1/2 trak. Would be using 3/8" heck of alot easier to pull and you get the same btu output as the 1/2"

OneHungLow

To hvhehcca

Thanks for taking the time...I knew the temp(193degrees) was looming there as a problem but couldn't get the calculations right. I am pumping 175-180 deg. to my baseboards and am trying to keep the radiant manageable in the 110-120 degree range, I think the 1/2" pex will deliver where the 3/8 would be limited by flow. In the addition I have the option of lower wall radiant but am still trying to work just the floor. I would like the formula for that 193 degrees...I have been crunching numbers for days. Thanks again Bill

CMadatMe

Wrong

I'm sorry but 1/2" will give you nothing more than 3/8 can except a 50' longer loop length.



Max Loop Length on 3/8 is 250

Max Loop Length on 1/2 is 300



I generally keep my loop lengths 200 or so and under. I like my loops as of even lengths as I can get them. Plus its like night and day when pulling..

Mark Eatherton

Grafting...

Haven't heard that term since my grandfather grafted a branch of a cherry tree onto an apple tree. It grew for many years, and the branch did sprout flowers and fruit. He called it his chapple tree...



Consider Ultra Fin for your project. It will be much simpler and easier.



ME

OneHungLow

ME

Thanks, I considered Ultra Fin but was informed that it is one difficult system to install and accurate heat delivery calculations don't seem straight forward. Yes, grafting isn't the right word.....this is more surgical, heart bypass with a new limb attachment better describes this project. Convert my conventional boiler/hwbb to a primary secondary system and pump the radiant zone and hwbb off that. I agree with Hvhehcca that 3/8 in shorter loops would better serve this install but what to do with these kitchens that have cabinets and fridge hogging up so much floor. I read a blog by another radiant installer that says to run pex in the full joist bay and if needed insulate under cabs with extruded poly....his explanation was the available area with heat transfer plates would draw the heat especially during off cycles....impossible for me to calculate. Is this method realistic? Thanks Bill

Mark Eatherton

Just trying to simplify your installation...

As for putting tube in, then insulating it from delivering heat to the space, that would be a waste of time and money. It either contributes to the real time load, or it doesn't. In your case, other than providing minimal protection for the in the outsdie wall, below cabinet potable water piping, there really is no benefit to putting heat beneath cabinets.



Reminds me of people who staple bare naked tubing to the bottom chord of a TJI, thinking that just because it is in there (the joist bay), it will work fine. It doesn't.



In order to maximize heat transfer, any design should use CONDUCTIVITY as the primary means of heat transfer, when ever possible. Doing so will require a lower operating fluid temperature (as you are aware), which adds complexity to the system design. Ultra Fin has been tested by numerous contractors on this site and has been found to work reasonably well. It does require significantly higher operating temperatures, but can deliver 25 btu's/sq ft/hour and eliminates the need for the extra pump and mixing station, and controls, and so on and so forth.



If you were doing this from scratch, my recommendation would be to go with as much conductivity as possible, and drive it with a condensing appliance, but your system distribution is fixed at high temperatures, hence my recommendation to go with the flow (high temp system). Doing the floor in a conductive mode will make it work better than having the Ultrafin in place, but at what expense, and probably no real $ operating benefit. A BTU is a BTU regardless of whether it is high temp or low temp.



There is a right place and the right time for most all applications. The key is to do the math first, and follow the math.



Personally, I don't pump a lot of heat into the kitchen because you have appliances in there that will already be dumping heat into the kitchen. If the floor is pumping heat into the space, and you fire up the oven or range, it will get uncomfortably warm in that space, then the adage of "If you can't stand the heat, stay out of the kitchen" gains new meaning, along with the definition of MEAN radiant temperature...



Also, the math used for doing loss calculations is an estimate, based on worst case scenarios that rarely occur for more than 2% of the time. It has also been my experience, that even on systems that I know for a fact were properly sized, that when I show up at "Design" conditions, and find the system doing a 50% duty cycle, that EVERYTHING is oversized by 50%...



JMHO



ME

OneHungLow

Re: ME

The Ultra Fin will get another serious look from me. It's really a convective system with the joist air space heating that it does. Their instructions for tube layout is different from a conventional pex install in that they do not "pull" the loops down a joist bay....they run once down the joist bay and return up another. Their alternate install runs pex perpendicular to the joists, both just odd and obviously labor intensive. The ability to use 180 degree water is it's main advantage, that would save me some mixing supply and monitoring return temps...also a pump or two. I will run the math again but I still don't see it solving the kitchen problem....a local heating rep I talked to today said "kick space heater, on it's own control because the room will be overheated too much of the time if you try to cram design heat into the radiant floor" And what about Ultra Fins claim to be compatible with all types of flooring even carpet! After all that number crunching on thermal resistances, is there a little bit of hot air in that claim? Does the ability to heat the air space in the joist cavity support the claim? Does it hold water? Thanks Bill