wild boiler sizing?

Cozy

Hello everyone, what a great site full of information.

Most of it is way over my head, so I will try to not annoy you.



I need a boiler for my radiant slab in a shop/office, but the problem I have is wildly different quotes on installing a boiler. Not so much on price, but on equipment power, so I am trying to get a rough understanding of how it works so I know if the installation is correct.

A calculation was done and 21,000 btu's an hour was the consistent number given. Give or take a few hundred. The building is more or less a garage without the garage door and well insulated.



The floor has non-barrier pex in it, so my understanding is I will need to keep the boiler separated from the pex/oxygen with a flat plate heat exchanger.



Is this the common way to do it?



How big of a boiler should I expect to need to transfer the boilers heat to the water in the slab?



How do you regulate the floor water temp if you have a boiler that fires at one "speed" and the required temperature for the floor is 100 degrees?



Thank you

SWEI

21,000 BTU/hr

Is smaller than any currently available high efficiency boiler.  You want to look at the minimum firing rate of the boiler -- the smaller the better for your application.  If the boiler is approved for it, you might be able to run without a separate HX by using a compatible (bronze or stainless) circulator and avoiding ferrous pipe & fittings throughout the system.

 

morpho

Good morning SWEI Oh, then how

do people typically heat a concrete floor when they have a small space or a well insulated building? I assumed it was a boiler that was used.



The smallest boiler that was noted on the quotes were 50,000 btu and the largest was something like 100,000.



Sounds to me like this will be a very wasteful way to make the heat needed.



I can't have one of the condensing / modulating boilers as there is no drain in the structure and I personally don't trust electronics and computers when they are near heat. They are going to fail. And given they are electronics, they are going to fail regardless of the heat or lack of it.

I once had a very illuminating talk with a stove repair guy who said kitchen stoves and ovens fail these days almost solely due to the electronics being in close proximity to the oven. Begs the question why they don't have them wall mounted away from the high heat.



When you say: "If the boiler is approved for it, you might be able to run without a separate HX by using a compatible (bronze or stainless) circulator..."



Do you mean run the boiler directly into the floor? I would imagine I would need some sort of mixing valve then as the water temperatures from the boiler must be well above the temperatures for in floor heating. And if the boiler is cast iron it must be affected by the lack of oxygen barrier tubing?



Do you know of any drawings of this kind of system?

I had a quick look at google and all the images showed systems that appeared to be for household water and heat. The plumbing looked so confusing I couldn't make heads nor tails of it.



So many questions all at once, sorry.

Thank you for the information.

It is clear why I never went into the trades, my head would explode, along with some-ones house I'm sure.

Eastman

You are Cozy?

You have a shop/office too?

morpho

No

but we are in the same sort of situation from what I can tell.

If cozey finds a solution I am interested in hearing it because I am at the end of the last thread on my rope.



I have settled on the fact I cant make a HWT work...so cozey...avoid that one if you can. I see the why's and how's of it not being a good choice.



I have poorly spec'd boiler quotes as well. Not sure how "wild" yours are, but mine seem out of line with what is being said here. 100, 000 btus would be a bit of overkill.



Though I wonder if the solutions isn't to put a big "vent" aka a hole in the wall and reduce my efficiency! Maybe that will work for all the small efficient places. We can call them "fresh air returns"

morpho

got it eastman....sorry cozy.

sorry Cozy...(spelled your name wrong AND Hijacked your thread).

Maybe there is no logical solution for small efficient buildings like ours.

Maybe a mobile home forced air unit and let your pex lay in the concrete until the technology catches up with the demand for smaller boilers.

SWEI

Small. efficient buildings

present a multitude of design challenges.  Just finding a suitably sized heat source is hard enough.  Throw in the fact that the overall energy usage of a small building is small to begin with.  Now insulate it well, and don't forget that a small building either generates or replaces a low monthly rent, and you have a "perfect storm" of unattractive ROI.



The Daikin Altherma comes in sizes as small as 18,000 BTU/hr and modulates down to 5,000 BTU/hr, but the first cost makes it a really tough sell around here.  We have a lot of winter sun in these parts, so proper passive solar design coupled with a small electric resistance boiler is our go-to answer right now.  If the boiler only operates a few hours per month, the fuel cost becomes a tiny component of the overall TCO.

Eric_25

DHW tank

I would use a 40 gallon sealed combustion DHW tank in this case. i have done it several times with great success. Use a SS or bronze pump and use components rated for use with potable water. If that is not an option than a Viessmann B2HA will fire down to 12K BTU's

SWEI

If the boiler is approved

for oxygen-containing water then you can use it directly with your existing non-barrier PEX.



> I can't have one of the condensing / modulating boilers as there is no  drain in the structure and I personally don't trust electronics and  computers when they are near heat. They are going to fail. And given  they are electronics, they are going to fail regardless of the heat or  lack of it.



If you install the boiler correctly, with a condensate neutralizer and a condensate pump, you should be able to dump the condensate outside.  The electronics in a modern boiler are designed to live where they do, in proximity to the moderate heat put out by the boiler.  At a supply temp of 186F (firing on a DHW call)  the HX is too hot to touch, but the boiler cabinet (where the electronics live) is just warm.





> When you say: "If the boiler is approved for it, you might be able to run without a separate HX by using a compatible (bronze or stainless)  circulator..."



e.g. Triangle Tube Prestige TriMax Solo (stainless HX, stainless piping, no problem with non-barrier tubing.)





> Do you mean run the boiler directly into the floor? I would imagine I  would need some sort of mixing valve then as the water temperatures from the boiler must be well above the temperatures for in floor heating.



A properly sized and commissioned mod/con will put out just what the floor needs and nothing more.  Many floor systems run at peak temperatures under 90ºF (really.)

Eastman

not the internet police

I was just confused.

SWEI

Another option

Costs more than a Cozy, but delivers real comfort with a minimum of fuss (and comes in small sizes) http://www.rinnai.us/direct-vent-wall-furnace

Cozy

SOlved for the moment

Thank you Swei we have gone with the suggestion you made for the wall furnace.

My contractor found a used one and this will keep us warm until the floor heating system can be hooked up with whatever makes sense.

SWEI

Let us know how it works out

They're good little units.



For some reason, they remind me of the old Monitor oil heaters.  New idea, looks different than what we're used to, but works so well that people just start buying them.