Need help with next step in my radiant heat system

As a consumer whom over time switched over to all radiant heat, I can tell you it is worth the time and money to install. I cannot say enough for this type of heating.
It sounds like all the pex was installed correctly. So there must be a manifold system in place for the load. You will need to tie in a source of heat to that manifold. I just finished an install of a gas micro boiler as a backup to my wood furnace. I plan to use it in the shoulder seasons and on getaways. Let me tell you there is a lot of plumbing that goes into a system like this. I spent much thought and a ton of time on the plumbing. I also live out in the boonies, and people react to you funny when you even mention systems like this around here. I called 5 local hvac guys, only 2 returned my call, and one offered me a job because his guys dont understand it.

Anyway, decide what you want your heat source to be, If you want to burn and mess with firewood then start there. I cannot recommend a micro boiler yet because I haven't used it enough to form an opinion on its performance.
Boilers (gas) can run from $1500 and up, I've seen some for as much as 4k and probably higher. A wood furnace will be more. There is much info here on wood furnaces, check out the sticky section at the top of the forum, look for "which stove should I buy"

But again, do yourself a favor and finish the radiant system, you will love its comfort!

Boonies or not start out researching wood boilers....after you narrow your search to a couple , contact the companies that interst you directly. As a potential new customer they should put you in touch with the nearest and most knowledgable people in your area...Those people will help with design and install...This is usually the more costly approach, expect to spend well north of 10G...If you want to muscle through it yourself, keep on researching, reading, and finding people familiar with these systems...good luck.

hi-liner said:

I purchased a home that has the start to a great heat system but was never finished. I have read alot and talked to local companies but no one seems to have the knowledge to make this work. One of the joys of living in the middle of nowhere comes with a price of learning how to do projects like this on my own. The previous owner had an in floor pex tube system installed with an on demand hot water heater. He said the system never worked properly and the best he could tell the on demand system just wasnt capable of keeping up. The house sits on about a 1600 square foot footprint, on a crawlspace. There is a very tall open ceiling with lofts on both ends of the home. Basically a 2 story home without the complete flooring upstairs. I am currently heating the house with a pellet stove and a couple of electric space heaters in the bedrooms on very cold nights. This isnt the most economical way to heat a home when -30 degree temps can be normal for extended amounts of time.

He left me the original plans, there is 2 zones and each zone has 4 loops of 325 feet using 1/2 inch pex tubing. Aluminum plates was used to secure the tubing to the underside of the floor between the floor joist, a reflective bubble wrap was installed over the plates and finally fiberglass insulation with paper backing was secured to each floor joist.
I really would like to install a wood burning boiler as a heat source for this system but I dont know where to head and find out exactly the proper procedure to make this happen. Any help or direction with this would be great.

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Been awhile since I messed much with radiant and the technology has changed alot in the last 25 years. But that said, rule of thumb was always to keep your loop size to 150'. In all likelihood the reason the system doesn't work is that the fluid in the 1/2' pex has given up its heat before it is halfway back to the source. You essentially would be trying to heat 1600 sq ft of living space with 600 lin ft of radiation. In your location 1 lin ft per sq ft of living space would be about right. You might get away with splitting the loops so that you have 8 shorter loops rather than 4, and start up the pellet stove when it gets to -30. It would double your effective radiation at very little cost and if you are well insulated that minor modification might all you need.

I have a number of rental units where we use Takaki (sp) demand water heaters as a heat source, some with radiant, some with euro style wall radiation and over 25-30 years have never had a bit of trouble with any of them. Most of the DWH units are at least 150k btu output which should be more than adequate to heat a reasonably insulated house the size of yours.

Someone else here, that knows more than I might pretend to, can maybe confirm or debunk my theory as to why the system doesn't work but it is something to consider.

If interested in wood boilers locally(if that's possible in MT),Obadiahs Woodstoves advertises here. They are in your state,although on the other side from you(you must be up on the highline?).
Anyways they have a good selection of different boilers on their website. http://www.woodstoves.net/

Have a good supply of firewood?
Last time I was across the highline,I didn't see too many trees up there!

It would be nice to see the temp difference in the supply and return.You might be right jaoneill I forget what my run lengths were.
I dont know what a boiler buddy system is hi-liner. I know I don't have it in my system.

Whoops; per my post above, written in haste. I see upon more careful reading that you have 2 zones, EACH with 4 loops. This doesn't change my advice, but again, if you split each of the 325 ft loops you would have 16 total, rather than 8; it should solve your problem.

Im pretty sure now my loops were 300' each. Works fine. I think that is pretty standard.

hi-liner said:

I purchased a home that has the start to a great heat system but was never finished. I have read alot and talked to local companies but no one seems to have the knowledge to make this work. One of the joys of living in the middle of nowhere comes with a price of learning how to do projects like this on my own. The previous owner had an in floor pex tube system installed with an on demand hot water heater. He said the system never worked properly and the best he could tell the on demand system just wasnt capable of keeping up. The house sits on about a 1600 square foot footprint, on a crawlspace. There is a very tall open ceiling with lofts on both ends of the home. Basically a 2 story home without the complete flooring upstairs. I am currently heating the house with a pellet stove and a couple of electric space heaters in the bedrooms on very cold nights. This isnt the most economical way to heat a home when -30 degree temps can be normal for extended amounts of time.

He left me the original plans, there is 2 zones and each zone has 4 loops of 325 feet using 1/2 inch pex tubing. Aluminum plates was used to secure the tubing to the underside of the floor between the floor joist, a reflective bubble wrap was installed over the plates and finally fiberglass insulation with paper backing was secured to each floor joist.
I really would like to install a wood burning boiler as a heat source for this system but I dont know where to head and find out exactly the proper procedure to make this happen. Any help or direction with this would be great.

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Start with a heat loss calculation.
From there you can use the curves published by the plate manufacturer or in the Uponor Complete Design Assistance Manual or the Zurn or Viega Radiant Design Manuals to get a good estimate on the amount of heat that can be delivered with your system at a particular water temperature and flow rate.
Then you can size your gas boiler (likely need a boiler not a water heater if you want to have a gas back up) and wood boiler.


ETA, I have radiant heat under my first floor. 768 sq ft, four loops of 1/2 inch pex stuck in Thermofin aluminum plate. Loop lengths are all equalized to 350'. A Grundfos Alpha pumps this zone on speed 2, total flow is 2.5 gpm, delta t is 15 or so.

I'm thinking about using these guys manifolds and advise for a 1200 SF addition. They are talking about low temp water so I may be able to use my return water. If so I wont have to change my current system.

http://www.radiantec.com/

The thing about using return water is that if there is periodically nothing returning water, you won't have it to draw from at those times. Eg. if you draw from a baseboard zone return, that zone might not be acitve at all the same times you want to draw from it for your infloor. May or may not be an issue but should be considered.

My system is always moving, the pumps run 24/7.

Thanks for the heads up.

Not much use for radiantec here. Do a little searching on heatinghelp .com for them.
We've run into more than a few of their so called "systems" and they are usually trouble. Most times it's the water heater they sold along with it. Just scratch their phone number from your list......

The 325' runs should be ok. Also sounds like it's insulated underneath as it should be. The question mark in the whole scenario is if the heat generated by that under the floor system is up to the task. As a rule of thumb, you can figure a max output of about 25-30 btu's per sq ft of floor surface without driving floor temps to the uncomfortable level.
Only a heat loss calc will tell you what your actual load is.

Aside from all that, and whether you go gas or wood source, we have had superb performance with systems like this which are able to change water temp based on how cold it is outside.
On many high efficiency gas boilers, that temperature reset can be accomplished directly by the boiler itself. The boiler targets a given water temperature at a given outdoor air temp. For example 110* water at outdoor 35*, 130* water at outdoor 20*, 150* water at outdoor 5* etc. This makes for nice long cycle times, eliminates a lot of noise from the plates (common from Radiantec materials) and keeps the boiler running in its peak efficiency range.

If you're going to go with a wood boiler this has to be accomplished externally to the boiler itself through the use of another control and some piping changes because a wood boiler does not like low water temperatures. Any wood boiler will do better with a system like this simply because it presents a little load all the time rather than full on/full off. You'll also get better results if you plan for thermal storage in your system.

The object of resetting the water temp on a plate system is to keep on/off cycles to a minimum. Every time the pex heats up/cools down, it moves in the plates due to expansion and contraction from the temp change. It's the nature of the beast.

Hi-liner, I have a similar layout to yours, no aluminum plates, huge open space with lots of windows and the in floor is not able to keep up with just the wood boiler alone. I probably should turn on the propane back-up at some point to keep a constant supply of 140* water circulating through my system, but that does defeat the purpose of trying to burn wood alone.