Hello All, Came across your website while researching for the umpteenth time a solution to my heating problem. Hoping you might have some insight into our heating problem that no one else has been able to resolve including my plumber. I’m also posting this in one other forum. I live on the in Alaska in a 75’ by 30’ Quonset hut style metal building that sits on a slab. It was built in 1993 and the original owner who built it has admittedly said he would greatly change what he did if he did it now. He installed two 1000’ loops of ½” polybutylene qest tubing that are heated by a Bock 32E oil fired Hot water heater(since replaced with a new one) and has a single Grundfos UPS 20-42f pump pushing water through both lines. As it is an open system, the Bock also fills all our hot water needs in the living area. The building is broken up into a 25’ living area on the south end and 50’ garage/shop area on the north side. From what the original homeowner remembers, one of the 1000’s loops goes side to side in the 25’ living area and the other 1000’ loop goes lengthwise front to back in the garage area. During cold spells below zero the heating system is lucky to maintain 50 degrees by itself. The only way we have been able to make it through the cold winters is to augment the heating system with a coal/wood burning stove. Several years ago, I purchased a Royall indoor wood/coal boiler but have never installed it due to my research on how the qest tubing would cause the cast iron boiler to eventually fail and running a heat exchanger with this inefficient system doesn’t seem to make it an option. I wonder if adding a pump pulling water through would help or even upgrading to a bigger pump, but have limited understanding on how head pressure would affect these ideas. Lately, my thought is to install two zone valves after the pump so that I can concentrate more hot water to the living area as it becomes much colder since the stove is in the garage. So from my limited understanding, my issues are: 1. Hydronic tubing runs are at least double of what they should be. 2. Polybutylene qest tubing allows oxygen into the water which will cause a cast iron boiler to breakdown more rapidly which will also create its own issue of iron particles in the system. Fortunately I haven’t had any other issues with the qest tubing. 3. The Bock hot water heater is probably overwhelmed to do the job even if all other factors were okay. 4. An open system, which may or may not be an issue depending upon how it is used? 5. Cement slab prohibits making any changes to tubing. I’m 6’ 5” and the ceiling in our living area is 7’ so running new tubing and then capping won’t work either. I’m sure there are other issues, but these seem to be the main ones. I appreciate any suggestions or input you may have that will help me.

Is there insulation underneath your concrete slab, and if so, what is it?

What is the source and cost of your electricity?

Are you SE or farther North?

Thank you for the response. Not sure on insulation, I asked but he couldn't remember. I believe there is, as he had blue board along the perimeter of the slab. Electric is from HEA: ◾$15.00 Customer Charge ◾$0.13780 per kWh Presently my monthly bill runs close to $300 year round as we run dehumidifiers to keep down the mold. I'm on Kenai Peninsula in the South Central.

Yeah, I've seen that before with still no insulation underneath. What is the insulation in the quonset overhead?

1000 feet is way to long for 1/2" pipe unless it is broken into smaller loops.

There is little you can do with pipe under concrete and you already have the wood boiler.

Install the wood boiler with a large water storage devise and install as series of wall or baseboard panels or possibly fan coil units to heat the air. Let the original unit do what it can to keep the floor warm but don't tie the systems together unless you use an exchanger in the storage tank to run the original system.

The Bock hot water heater is probably overwhelmed to do the job even if all other factors were okay

Does the burner run continuously on cold days? If not, then you have some excess capacity and could look at fan coils to supplement your floor radiator. Or use them to distribute heat from your wood boiler.

I don't know your climate or oil prices, but at least for some weather, an air source heat pump is likely to be more cost effective that oil.

Yes, adding a pump will increase flow through too long tubing loops.

The reason the original owner "can't remember" is because he doesn't want to admit how stupid (or cheap) he was to build a radiant slab without insulation. Once he got informed, the blue board was probably installed on the edges after the fact. Because of that, much of the heat you put into that radiant slab will be wasted. You can rent or borrow an IR camera to help you core the floor and see if there is insulation under there, but you probably won't find any.

I'd sell that wood fired boiler thing and buy a proper wood stove (with outside combustion air) to go in the garage area and a Fujitsu ductless mini to heat and A/C your living area. You can still run the oil radiant system to keep the garage unfrozen and to keep down the bone-chilling cold of an unheated slab, but much of that energy will continue to be wasted. You will do much better with the comfort and efficiency of the ductless mini and you can stoke the garage wood stove with scrap to bring the temperature up when you need to work in there.

If that pump is 20 years old, you might also want to make sure it is still delivering original flow rates.

And, you will want to see how much "blue board" there really is along the slab and how deep it goes in an effort to stem that heat loss.

2" thick, 4' wide horizontal "wings" of foam can be added just under the perimeter soil surface and will be partially effective at a much lower installation cost.

In some cases, abandoning a radiant floor and covering it with 3/8" foam and carpet/rug might be best. Ceiling mounted radiant panels (radiating the floor) might keep it from feeling too cold.

I'd just keep using the slab to some degree because the cost, disruption and time of taking up the floor and laying down insulation would be substantial. Plus, you don't want frost to get under that shallow slab. Not TOO worried about that on the Kenai, but other places it could be an issue. Also keeps you from freezing your feet. That can be very uncomfortable. Lowest cost fix is trading the wood fired boiler for a stove and the ductless mini addition.

What did the cheapskate builder do for windows?

When does it get mold?

Right, this is a hopelessly bad design. So don't expect much or spend much trying to improve it, and save your money for your next home. 300 feet is about the max circuit length for 1/2 inch pex.

Not sure what the head capacity /flow is on your current pump, but you might check,
Assuming you might need about 1 gpm on flow, both loops running, 30% glycol 120 degrees the per foot head is .0448
You will need a pump that can push 48 feet of head capable of 2 gpm.
Assuming you might need about .5 gpm on flow, both loops running, 30% glycol 120 degrees the per foot head is .0139
You will need a pump that can push 14 feet of head capable of 2 gpm.
1,000 foot loops are a wrong choice with out a doubt, but these are the numbers on the pipe head to place part of the problem in perspective.
Not saying it is what you will need more to the point an example of two water flows, I suspect you are in the 3/4- 1 gpm range to do much good, but a heat loss and backwards design based on what you have might be a good start to see the possibility.
You have less than 1 foot of pipe per square foot,
long loops, might look at raising the delivered h20 temp to the 130+ range.agreed that this is a hopelessly bad design.
good luck
Dan

Posted By jonr on 21 Nov 2013 10:10 AM
2" thick, 4' wide horizontal "wings" of foam can be added just under the perimeter soil surface and will be partially effective at a much lower installation cost.

In some cases, abandoning a radiant floor and covering it with 3/8" foam and carpet/rug might be best. Ceiling mounted radiant panels (radiating the floor) might keep it from feeling too cold.

In parts of AK you really can't do the wing-insulation thing, since the stability of the soil the slab rests on is counting on permafrost.  I don't think that's the case on the Kenai Peninsula, but in much of the interior you absolutely MUST insulate under the slab (radiant or not) to keep it from heaving & sinking.  (Even thermally isolating pier foundations is necessary in some places- the bottom of the pier being supported by permafrost.)

The problem with a 1000 foot circuit is that you can't physically pump the flow rate that is required to maintain an acceptable temp drop across the circuit. As you increase the flow rate to try to achieve the required flow rate, the hydraulic friction and associated required pump head gets too large. So the best youcan achieve is a floor that will have an unacceptable temp gradient.

We designed a fully integrated hydronic system for a client on the Kinai Peninsula a few years ago. Fortunately we specified the insulation below slab and above. An outdoor wood boiler is the main source of heat since beetles killed all the pines a wood is plentiful. The wood boiler heats the steel building, which house shop, garage and living quarters on two levels. The main floor is radiated, PEX in slab and the upper levels by European style steel wall panels and the hot beds (plants won't grow in sub-freezing soil). A propane-fired Triangle Tube Solo 110 with Smart Tank water heater serve as backup,--rarely used since propane runs over $5.00/gallon on the Kenai.

There is no permafrost on the Kenai save a random glacier or three. A good part of coastal areas are comprised of sandy silt (glacial) and the frost depth is less that 4 feet--about the same as we have here in Minneapolis.

When we find slabs that are not insulated and indoor design temperature dictate, we insulate, install a proper PEX tubing pattern and cover all with 1.5" of concrete.

Radiant ceilings, wall panels or--if you must--hydro fan coils hooked up to the outdoor with propane backup. But get some design help before you spend money. There are a few good mechanics on the Kenai but few can claim design experience.

And, the fishing is great!

I ran into the same problem with a heat exchanger and got a pretty good solution from houseneeds.com. My loops are only 250' but I forgot to add the 120' of copper coil in my heat storage tank. Houseneeds broke the system into a primary and secondary loop to add a second pump. Look at the closely spaced tee in this design: http://www.houseneeds.com/learning-center/hydronic-boilers-learning/hydronic-boiler-5-zones-indirect-tank-2. (In my system, a third pump/coil puts heat into the tank from a wood stove boiler and the primary takes heat out.)

You could also use this approach to divide hydronic into a low-temp circuit with mixing valve for the floor, and a high-temp circuit for radiators as and where you need them.

But I'd figure out where the problem lies first. I am unschooled in matters hydronic as you might guess, but I'd start with an analysis of temps in and out to decide if you lack pex (acceptable temperature difference) or insulation (unacceptable difference.) Or both.

Exactly right Todd. You can have several thousand of feet of pex in the floor, but you have to accomplish this via multiple circuits so as to not exceed the max pex length for the design parameters. Always best to determine what you have and then do a ROI analysis to determine how best to get where you want to be.

I wonder what's happening in Hydronic Hell on the Kenai.

Hmmmm.... -13F. Probably not too dry there, either.

I hope the fishing is good.

As a owner of a hydronic floor.. Two buildings in fact. Do you notice the outside edge of your perimeter slab showing signs of heat loss? melted snow ? Early flowers/grass/flora? I'm inclined to think the slab is losing As much as 50% of its heat out of the perimeter. Long narrow building, Too long of loops. I suppose it has cyanate yellow insulation stuck to the Arches Suggestion , insulate as advised . Buy the harbor freight thermo laser gun... Go looking. shoot the edges the center etc,... The picture will start to form. Good luck... At the risk of being shot here,, The lack of insulation under the center of the floor is not the main problem. 50'F soil vs 10'F perimeter temps and the delta tells. Building our 3 rd now. Skin IN the game. Helped on several. Radiant Technologies in Connecticut had a old NASA advisor. The Apollo didn't have 14 feet of pink fiberglass on it. Moral. A little goes a long ways ". You gotta have something in the right place to work." In Alaska in the 80's,, I saw the trick of out AND down perimeter insulation. They swore by it. Best Wishes..

You are correct...the vast majority of heat loss for a slab-on-grade floor occurs at the exposed perimeter. This is why a slab-on-grade floor heat loss analysis is based on exposed floor perimeter and is NOT based on area as is the case for ceilings, fenestration, and walls. This is also why perimeter insulation is more important than under-slab insulation and why many of us prefer ICF buildings with floating slab floors. However, most folks want to minimize ALL the heat loss and not just minimize the majority of heat loss. So many of us insulate under ALL the slab area too. We have worked with folks in Alaska where their slab-on-grade floor insulation was specified in feet and not in inches...