Water to Air HX btu output vs input water temp

[3fordasho]

I'm starting to realize that heating 3 separate structures with 4 different wood burning appliances is not sustainable long term ;-).

One of the structures is suitable for boiler with storage and lots of wood storage. First thought is a Garn JR because of simplicity and I am with in 100miles of their manufacturing facility.

So of the three structures needing heat, the house being the main concern is currently set up with 120kbtu propane FA, Tundra wood furnace tied in parallel, and a Progress Hybrid on the main level. The Tundra would go away, Progress Hybrid would remain for when I want to look at a fire.

Now to my question - plenum in the FA furnace is large, can probably fit a 22x25 or somewhat larger HX. Trying to determine how low I can go on storage temps and get any meaning full output. Output ratings I've found so far are all at 180F input temp, ~21 gpm , and CFM air flow. Looking for a calculator, output vs input temp chart, or even what others have experienced.

 

[stee6043]

I found the lowest useable temp to be 140 with my "off the shelf" water-to-air heat exchanger. If I were to do it again I'd have a custom coil built for the plenum rather than just buying one that fits dimensionally. With a proper coil you can go lower with your input temps and still get reasonable fan run times. At 140 my furnace fan was running for a noticeably longer time per cycle. Not desirable...

 

[dogwood]

After reading Pybyr's posts on the subject a few years back, I ordered mine through Nationwide Coils, www.nationwidecoils.com/ . I spoke to someone named Ross if I remember. They will custom design a water to air hx to meet your specifications, give you a quote and send you a submittal sheet with more info on it than anyone could possibly understand. Mine was designed to work to work with temps down to 140F. You have to know what the air flow of your furnace is when you call.Their phone number is 888-549 9616. My oversized w/a hx from them has worked as designed three years running now. If I had to do it over I would have had specified larger fittings to connect to my piping.

Mike.

 

[tom in maine]

I am associated with another company that has air to water heat pumps. We also offer water to air fan convectors that are a great heat distribution device that can operate down to 90F doe space heating.
I am usually using one at 120F. There are three sizes and they are very quiet.
They are on (broken link removed)

 

[jebatty]

If you need supply water much hotter than 140F, I suggest you talk to Garn as how the Jr would work to meet your needs.

 

[Woodfarmer1]

It is my experience that the Garn jr will not deliver. I can get just over 160* to my secondary but that temp is not sustained for more than a couple hours. It likes to sit at 140*.

If it was installed right beside the furnace those times may improve.

I fired the boiler last night at 11 (after Canada won Gold at the World juniors) so by 1am the Garn temp would be say 190* +. For my radiant heat it would be around 160* + usable.
This morning at 8am, the Garn was at 146* and the usable at the secondary was 124*.
I have rads and in floor.

 

[jwise87]

Depends on what you are used to on the usable temp. We had a heat pump in our house that put out luke warm air at best, so I put the kick out temp all the way down at like 80* for when it would use the heat pump and when it would use the boiler, and it felt like the heat pump. However I usually ran my temps somewhere between 155* and 175* depending on temp. I was heating a 2400 sq/ft newer built house and had about 225 gallons of storage and if I let my fire went out in the night it would drop maybe 50-75* by morning. As far as storage goes on wood boilers the more you have the harder it is to recover after a mistake like letting the fire go out.

 

[maple1]

As far as storage goes on wood boilers the more you have the harder it is to recover after a mistake like letting the fire go out.

Not sure about the wording on that one. I don't think there is any disadvantage to more storage, recovery wise, as long as things are plumbed right. Even if my storage is stone cold, I can have 160 water going to the house 20 minutes after lighting a fire. So it recovers quick and size of storage doesn't matter. It takes longer to recharge bigger storage, yes, but if you put the same amount of heat into bigger & smaller storage, they should put out the same amount, again, as long as plumbed right (stratification is key). You have to burn longer to fully charge bigger storage, yes, of course, but it will heat your house for a correspondingly longer time, after the fire is out.

 

[rkusek]

It depends if you are used to lukewarm heat pump output temps or much warmer gas forced air heat register temps. My off the shelf WA/HX was able to maintain the 68 setting we had using only 100-120 degree water this past week with below zero temps. My load bridged on the -19 night and woke up to 64 degree house. Definitely cannot bring it up to temp with 100-110 degree water though. Kicked on emergency backup 15kw heat on the furnace for an hour and only gained a degree. Output was not much warmer than wood HX output either. I think the custom HX would be worth the money. You still have the LP option to cover the rare catch up situations. The Garn is something I wish I had done for simplicity reasons but I don't mind the blower fan running more. Some people might though.

 

[rkusek]

3 structures? Wouldn't the 1500 be better than the Jr?

 

[rkusek]

Eko 40 with 40 degree 30x60x14 pole barn and 64 degree house wouldn't go above 159 for the entire burn on that cold morning. Most winter days it works just fine though.

 

[3fordasho]

3 structures? Wouldn't the 1500 be better than the Jr?

Perhaps. Besides the house, one of the structures is where the boiler will be located (24x48' insulated) and keeping it above freezing will be acceptable, then there is a smallish insulated office/well equipment room in the 60x104' pole barn that I keep at 40F. So two of the three structures have pretty small heating loads. House is 3400 sqft and well insulated and sealed for a 1982 build.

 

[jwise87]

Not sure about the wording on that one. I don't think there is any disadvantage to more storage, recovery wise, as long as things are plumbed right. Even if my storage is stone cold, I can have 160 water going to the house 20 minutes after lighting a fire. So it recovers quick and size of storage doesn't matter. It takes longer to recharge bigger storage, yes, but if you put the same amount of heat into bigger & smaller storage, they should put out the same amount, again, as long as plumbed right (stratification is key). You have to burn longer to fully charge bigger storage, yes, of course, but it will heat your house for a correspondingly longer time, after the fire is out.

I was not thinking of added storage when I said that, I had the volume of the water in the water jacket in mind. It would take me a hours to get my water up to temp in my old stove. I pulled water from near the bottom and returned it to the top so I would have constant circulation in water jacket, but that meant I was in trouble if my temps dropped.

 

[3fordasho]

If you need supply water much hotter than 140F, I suggest you talk to Garn as how the Jr would work to meet your needs.

It is my experience that the Garn jr will not deliver. I can get just over 160* to my secondary but that temp is not sustained for more than a couple hours. It likes to sit at 140*.

If it was installed right beside the furnace those times may improve.

I fired the boiler last night at 11 (after Canada won Gold at the World juniors) so by 1am the Garn temp would be say 190* +. For my radiant heat it would be around 160* + usable.
This morning at 8am, the Garn was at 146* and the usable at the secondary was 124*.
I have rads and in floor.

Seem to be reading here that the Garn shines best with low temp emitters like radiant floor. Not an easy thing to retrofit into existing structures.
Garn rates their boilers storage from 195f-120f. Would be nice to get some usable heat down to 120f but don't know if that is possible in a water to air HX. Should I be looking at different boiler designs? Not locked into a Garn by any means.

 

[gfirkus]

I’ve had water temp down to 120 and it still blew enough heat. Get the largest hx that fits your plenum . Make sure the supply goes to top of hx. I only have 1500 sf ranch house tho. Check out the Switzer boiler. I had about $750 into going to get it. Overall it was cheaper than the garn and is pressurized. Treat the water once and your done.

 

[3fordasho]

After reading Pybyr's posts on the subject a few years back, I ordered mine through Nationwide Coils, www.nationwidecoils.com/ . I spoke to someone named Ross if I remember. They will custom design a water to air hx to meet your specifications, give you a quote and send you a submittal sheet with more info on it than anyone could possibly understand. Mine was designed to work to work with temps down to 140F. You have to know what the air flow of your furnace is when you call.Their phone number is 888-549 9616. My oversized w/a hx from them has worked as designed three years running now. If I had to do it over I would have had specified larger fittings to connect to my piping.

Mike.

Thanks for that link - they provided a quote and specs with in minutes of submittal. If I'm reading the submittal data correctly I should still see 60k btu output at 120F water temps.

 

[3fordasho]

I’ve had water temp down to 120 and it still blew enough heat. Get the largest hx that fits your plenum . Make sure the supply goes to top of hx. I only have 1500 sf ranch house tho. Check out the Switzer boiler. I had about $750 into going to get it. Overall it was cheaper than the garn and is pressurized. Treat the water once and your done.

Thanks for the reminder about Switzer, they will definitely be considered. Especially after reading that thread back in 2011 about the corrosion issue in the Garn, though seems to be possible in closed systems as well.

 

[surefire]

I think that corrosion issue was due to improper operations ie boiling and lack of a water test before summer layup, IIRC.

 

[surefire]

What were your specific details provided to Nationwide Coils? I might be missing something, but doesn't the SCFM seem really high on the submittal?

 

[3fordasho]

What were your specific details provided to Nationwide Coils? I might be missing something, but doesn't the SCFM seem really high on the submittal?

Info I gave them but need to verify further. Thanks for pointing out that parameter maybe off.

 

[dogwood]

Thanks for that link

Your welcome. That's the same format submittal sheet they sent me years back. The Air Flow (SCMI) listed on my sheet is 1320 and I've a fairly big furnace. Check your furnace's manual to be sure. Some have multiple air flows and settings.

When the original furnace died a furnace service person had to do some adjustments to the new furnace to get the airflow matched to the w/a heat exchanger's design parameters. Nothings ever easy. Good luck

Mike

 

[surefire]

Info I gave them but need to verify further. Thanks for pointing out that parameter maybe off.

Tim, was there any follow up on that parameter?

 

[3fordasho]

Tim, was there any follow up on that parameter?

I am going to have them recalculate with 1400 cfm air flow (after reviewing the furnace specs this seems more realistic)
I can also go larger HX if I move it up higher in the plenum but will have to go from 6" coil thickness to more like 4". Wish I had their sizing program so I could play with all these parameters myself.

 

[3fordasho]

Tim, was there any follow up on that parameter?

New coil specs @ 1400 cfm. Changed coil size to 26 x 26"x 4". 55kbtu delivered @120F. Should still heat the house at 120F supply temp.

 

[surefire]

Nice. You're okay with a decreased output of 6.3kbtu? Maybe not a big deal.