Condensing Boiler Drain

[Logician]

I was planning on using a condensing boiler for the in slab heat on my new garage. The garage has no other plumbing and no drain. Are there any options to drain the condensate to the outside? I know it can have freezing problems. Should I just go to a non- condensing boiler? Any feedback appreciated. Slab pour is next week.

 

[Ron Lombardo]

I was planning on using a condensing boiler for the in slab heat on my new garage. The garage has no other plumbing and no drain. Are there any options to drain the condensate to the outside? I know it can have freezing problems. Should I just go to a non- condensing boiler? Any feedback appreciated. Slab pour is next week.

Poke it out the wall or into a bucket ... its so minor you could just drill a hole in the slab.

 

[aandpdan]

It'll kill the grass if you just dump it outside. It is pretty acidic, probably wreck concrete too. It will damage cast iron. You can run it over some lime chips to help.

Most condensing boilers have a safety switch so if the condensate drain blocks up the boiler will shut down.

I wouldn't call it minor either. In the winter, I have a pump, it empties at least once a day (efficiency at work).

Can you dig a drywell maybe? Run a pipe a couple of feet underground so it doesn't freeze up?

 

[brewchief]

Can you dig a drywell maybe? Run a pipe a couple of feet underground so it doesn't freeze up?

This is what I would do.

 

[larry4406]

The drywell sounds good. I have drilled basement slabs and run the drain thru the slab to the gravel bed under the slab. From there, the condensate joins the groundwater and perks thru the gravel and becomes one with the groundwater.

 

[Logician]

Plumber says condensate may be 5 gallons a day in winter here in northern MN. Is this correct? 30x32 garage with 16x32 space above. I will discuss the drywell with my concrete contractor. What should a drywell cost? The site is all rock/ gravel with great drainage. Also, no grass. I noticed that nobody has said to forget the condensing boiler which was my first thought. I am planning on R12 doors, R19 walls, and R44 ceiling insulation, leaning towards open cell Icynene spray foam. With a natural gas boiler, I am planning to keep it at 70f all winter!

 

[HoosierBuddy]

Plumber says condensate may be 5 gallons a day in winter here in northern MN. Is this correct? 30x32 garage with 16x32 space above. I will discuss the drywell with my concrete contractor. What should a drywell cost? The site is all rock/ gravel with great drainage. Also, no grass. I noticed that nobody has said to forget the condensing boiler which was my first thought. I am planning on R12 doors, R19 walls, and R44 ceiling insulation, leaning towards open cell Icynene spray foam. With a natural gas boiler, I am planning to keep it at 70f all winter!

A non-condensing boiler is going to be about 20% less efficient.

IIWY I'd stay with a condensing boiler.

What I did on mine (which is sort of mickey mouse, I admit) was to run my drain to a tee. One side of the tee goes through the wall of the garage and drains onto the grass....and it hasn't killed anything. The other side of the tee goes up an inch or so, and then over to a 5 gallon bucket.

Two or three days during the winter the outside drain will clog with ice and it will drain to the bucket. Sometimes the bucket overflows to my floor drain. I haven't had any concrete issues as a result.

Floor drains are really nice, but can be a real problem to get to code depending on your local jurisdiction. I didn't have any code issues so I put them in and am very glad I did. If I had it to do over, I'd have run a condensate line under the slab to the floor drain...but I can't do that now.

Phil

 

[koditten]

20% more effiecient for a home. Hard to make those numbers work for a shop. I did the math for my shop. My 1400 sq ft will take me 30 years to break even using a non condensing boiler . I decided on a non condensing boiler.

The only advantage I could come up was the ability to use pvc for a stack.

I guess I will be the first to say forget the condensing boiler. Just my opinion.

KO

 

[aandpdan]

If you plan on keeping the temps steady and with the water temps low so that you are condensing, you are going to be making lots of condensate and won't be using much gas.

Do you have an outdoor reset on that boiler?

Once you start playing with the thermostat you cancel out the savings.

 

[beemerguy]

The only condensate you get from a condensing "boiler" is from the gas side. The byproducts of burning a hydrogen rich fuel like natural gas or propane are water and carbon dioxide. The amount of condensate will therefore be proportional to the amount of gas you burn. The water side of your "boiler" is most likely going to be a high temp hot water and no boiling will be taking place. You will probably use an ethylene glycol mixture so that freezing will not be a problem. Most condensing combustion systems drain into a float operated pump. You can run this thru tubing as discussed earlier with the outside drain and bucket back-up. They sell a neutralizing filter that allows you to drain to sewer but not needed for your application.

 

[aandpdan]

Correct, it really isn't a boiler as such. It's more of a water heater.

In a concrete slab the water temp should be about 95 degrees max. Any hotter and you'll be dancing on the floor.

 

[freds fuel]

In Pa. we use a condensate pump to the outside. No problems as long as the hose outside drains empty.

 

[Jackfre]

One of the reasons to use a condensing boiler is they frequently, but not always come properly and fully equipped with the outdoor reset controls and modulating burners to maximize efficiency. As well, they are usually sealed combustion and with the work that goes on in a garage and the **** we have in them, you definitely want sealed combustion. The condensate will typically have a Ph in the 3.2 range. Pretty hot on a concrete floor. If I was putting it below the slab I'd drill a large enough hole to get a well point thru and go a few feet down. If that water pools against the concrete it will over time consume it. You can use a neutralizer lit. Fill it with limestone chips and it will do its thing. Make your own with some 3"PVC a couple feet long, cap on one end and threads on the other. Get a couple barbed fittings on the end and connect it.

I once had a customer use a furnace I was representing as a construction heater. He set this condensing furnace on his new concrete floor, put a supply plenum on the top which he secured to the floor joists. He called me in the spring and I had to go visit the place. The furnace was hanging from the floor joists. The bottom 4" of the furnace were gone due to rust. This furnace had a 12ga base plate on it. His new basement floor had a 6' radius that dished out to about 2" thick. The exposed aggregate looked like it had been run thru a rock polisher.

Whatever you decide, why don't you measure the amount of condensate at different outside temps for your own info and report back on what you find. Whether oil, NG or LP, there is a potential per gal or therm of about 1.1 gal of condensate. You won't see that much, but it will be interesting to know how much there is.

 

[brewchief]

One of the reasons to use a condensing boiler is they frequently, but not always come properly and fully equipped with the outdoor reset controls and modulating burners to maximize efficiency. As well, they are usually sealed combustion and with the work that goes on in a garage and the **** we have in them, you definitely want sealed combustion. The condensate will typically have a Ph in the 3.2 range. Pretty hot on a concrete floor. If I was putting it below the slab I'd drill a large enough hole to get a well point thru and go a few feet down. If that water pools against the concrete it will over time consume it. You can use a neutralizer lit. Fill it with limestone chips and it will do its thing. Make your own with some 3"PVC a couple feet long, cap on one end and threads on the other. Get a couple barbed fittings on the end and connect it.

I agree 100% with the above on the outdoor reset and sealed combustion, one other benefit to most condensing boilers is there ability to run at cooler temps eliminating the need for mixing devices to bring the boiler water temp down to a temp suitable for infloor heating.

 

[Logician]

Thanks for all of the comments. We have stubbed in a 3" drain that runs to the outside below grade where I can dig a drywell of some type. I will insulate it with some foam to keep it from freezing.