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Old 02-02-2020, 10:33 AM   #1
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boiler vs hot air ... confused


Hey!


So, I just finished building a house ... two story ... 2400 sq ft each floor ... 4800 total ... in VT where it gets cold.


I have natural gas.


I choose a forced air furnace ... sized it ... choose a 2 stage 120,000 btu unit (about 80,000 on low).


Works great ... seldom ever goes to high.


So, I am now building a workshop.


3 bays isolated from each other .. 1000 sq ft each (20 x 50 each with 16 ft ceilings) .. plus an office .... plus a 1000 sq ft loft ... so about 4500 sq ft total.


Because there are now 5 distinct areas with one (the office / bathroom, so really 6 ... it is much smaller than the others) ... I was thinking about hot water heating.


Originally I thought just a single large furnace with zones (like I did to the house ... I have three zones).


Then I thought about 3 or 4 simple single stage furnaces ...one for each ...but that get a bit pricey for a workshop.


Then I thought about a hot water system. Simple enough ... tankless boiler (like my hot water heater in the house) .... a bunch of PEX and a couple of ceiling hung radiators with fans in each area.


Now, here is my problem ....


I look at Home Depot ... 199,000 BTUh boiler .... 9.3 gpm ... 100 - 180 deg heating water.


I look at a Modine heat exchanger chart .... HSB/HC 108 ... at 9.7 GMP and 180 deg water, I am only getting out about 70,000 BTUh ...why ?????


If the boiler has a 199,000 BTUh rating but using it's full capacity I an only getting 70,000 BTUh out ... what happened?????


I am a true DIY guy (thus it took 7 years to build a house) .. have put in a few furnaces (gas and electric) and A/C units ... all worked great.


I have just never touched a hot water boiler before.


If I can get the full boiler heat out of the exchangers, I would have no problem ... but less than half will never heat the building.


Can anyone explain what is going on or if I am making some kind of mistake reading the tables.


Thanks so much .... Mike
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Old 02-02-2020, 11:04 AM   #2
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Re: boiler vs hot air ... confused


Quote:
Originally Posted by xtal_01 View Post
So, I am now building a workshop.
... so about 4500 sq ft total.

Because there are now 5 distinct areas...
I have just never touched a hot water boiler before.
Now's the time to move up to that.
A FHW boiler with zone control set up.

It would have been better for the house as well.
Or do you really need to have air conditioning up there in VT?

Last edited by TarheelTerp; 02-02-2020 at 11:08 AM.
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Old 02-02-2020, 11:26 AM   #3
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Re: boiler vs hot air ... confused


Funny you say that about the A/C ...


I put the coils in the furnace when I installed it but the outdoor half is still sitting here on a skid not installed. With only an average of 5 days a year over 90, and a super insulation job (I pay less than $200 in the coldest months), we just never needed it.


I choose hot air because my wife is disabled and likes to change the temperature fairly fast. If she goes downstairs, she wants it to heat up from say 68 to 74 in a hurry.


Forced air does this ... a boiler with radiators would take a lot longer.


The workshop is another story.


I plan on only heating the area I am working in and just keeping the rest of the shop above freezing (say 45 or 50 deg). Once bay of the shop will just be for storing our RV ... it will be much easier to store not having to winterize it all the time. We travel a few times each winter (go north not south ... duh) ... so each time I need to drain it and winterize it. If I keep it above freezing it would be so much easier.


Anyway ... no one in the area want to help. Local places say I need to go through a contractor ... had this problem with the house ... ordered everything online.


I just want to make sure I get the sizing right. SO far it just doesn't make sense.

Thanks .... Mike
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Old 02-02-2020, 11:58 AM   #4
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Re: boiler vs hot air ... confused


The 108 is for steam. If you want closer to the boilers rating, you would need to go to the 258.
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Old 02-02-2020, 12:03 PM   #5
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Re: boiler vs hot air ... confused


I've worked in shops with hanging heaters attempting to force hot air down. To get warm I usually went out and got on the cat walk between a couple of 7,000 cubic engines with cherry red exhausts.

Attempting to force hot air down didn't work a hundred years ago and it still doesn't work very well today. There is discussion open now to that effect with a central system in an attic trying to heat a cold first floor, and many many others.

If you want something reliable, even when there may be electric power outages because of an ice storm etc., you'll install a thermostat controlled wall heater in each individual shop bay and at least you'll have something similar to a fire place or wood stove to back up to and warm your posterior.
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Old 02-02-2020, 01:08 PM   #6
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Re: boiler vs hot air ... confused


Just depends if your going to keep it all heated all the time, or are going to go out and want to turn the heat on for the day. Unless your going to keep it warm all winter, I wouldn't do hot water of any kind, unless they were the kind of heat exchangers that are fan forced. So if your shop has garage doors, what happens when you open one of those doors in winter to unload something? You will lose all heat in that bay instantly and expecting a hot water system to recover quickly isn't going to work. I would go with your first idea of either a zoned forced air furnace, or 3 smaller forced air furnaces.
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Old 02-02-2020, 01:08 PM   #7
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Re: boiler vs hot air ... confused


Quote:
I've worked in shops with hanging heaters attempting to force hot air down. To get warm I usually went out and got on the cat walk between a couple of 7,000 cubic engines with cherry red exhausts.

Attempting to force hot air down didn't work a hundred years ago and it still doesn't work very well today. There is discussion open now to that effect with a central system in an attic trying to heat a cold first floor, and many many others.
Forced air from ceiling works just fine if the duct system is done right with return near the floor.

It's not ideal comfort wise - drafty.

The attic systems you speak of don't heat the first floor properly due to poor design - no room by room load calc, rules of thumb only and using undersized flex ducts which really restrict airflow on long runs.

----------------------
There is no reason to zone the typical heat only system - deliver the correct amount of heat to each part of the building and you won't have major temperature differences between rooms.

If you insist on zoning, hot water is definitely a better choice.

In a workshop, if it will be dusty forced air furnace may not be the best choice unless you're fine with using expensive high merv filters (use media filter cabinet) and changing them frequently.

The unit heaters are less affected by dust with them using axial fans.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 02-02-2020, 01:09 PM   #8
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Re: boiler vs hot air ... confused


Quote:
I look at Home Depot ... 199,000 BTUh boiler .... 9.3 gpm ... 100 - 180 deg heating water.


I look at a Modine heat exchanger chart .... HSB/HC 108 ... at 9.7 GMP and 180 deg water, I am only getting out about 70,000 BTUh ...why ?????


If the boiler has a 199,000 BTUh rating but using it's full capacity I an only getting 70,000 BTUh out ... what happened?????
Are you looking at condensing boilers?

They do need low return water temps to deliver rated output.
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Old 02-02-2020, 02:21 PM   #9
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Re: boiler vs hot air ... confused


Thanks for all the input!


Since I am starting with a blank sheet, I am open to any ideas.


One bay is for metal working (I am a machinist by trade) ... lathe, mill, ... not much dust.


One bay and the loft is for storage .... again, not much dust.


The "middle" bay is open .... I do some welding .. a bit of wood working (not at the same time ). This could have some dust and will require the most filter changes.


Yes, the unit I am looking at is an exchanger with a fan.


Yes it is rated for steam but there is a conversion chart in the manual (looking at it online) that is labeled "hot water performance data ..." The is a conversion factor to multiply the rating by.


I am going to heat all bays .. but just above freezing. As I said, this will help me from having to winterize my RV.


I am thinking with a forced air or a radiator with a fan, I should be able to heat one bay or a bay and an office up in say an hour or so before I go out (all my thermostats in the house are on wifi).


I am definitely worried about the 16 ft high ceilings. I have been thinking about exiting the air at floor level .... putting in ceiling fans ..... putting in a ducted blower to take air from the ceiling and duct it to the floor ...


Way too many ideas!


So going back to my original question .. which may eliminate the boiler idea ... if I have a 199,000 BTUh boiler ... Home Depot states 9.3 [email protected] deg. Will I get even close tot he 199,000 BTU's? As I said, using just one exchanger, it looks like I will only get 70,000 BTU's


Even if I use 8 of there small units (HSB/HC 18L) I would reach my max flow of the boiler and still only have about 80,000 BTU's.


And maybe I am looking at the wrong data for the exchanger ...



I appreciate any help!


Here is a picture of me painting the pad ... figured it was easier to do before I started building: https://www.facebook.com/pg/VermontC...15582135471977


Mike
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Old 02-02-2020, 02:33 PM   #10
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Re: boiler vs hot air ... confused


Before you poured the pad would have been the time to install in floor radiant heat.



With 16' high ceilings, radiant tube heaters would be my choice.


But if you really want to use fan coils. Don't forget you should make it a glycol system, so incase you lose power, the heating pipes and fan coils don't freeze and burst.
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Old 02-02-2020, 02:44 PM   #11
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Re: boiler vs hot air ... confused


Yes, I could have done radiant ... there is actually 2" of blue foam under the pan and the edge is insulated 24" down and 24" out (needed for frost protection.


I made the mistake of pouring the pad when I started the house.


And honestly, it is the biggest mistake I made. The concrete contractor I hired convinced me this was the way to go. He was 70 at the time .. about to retire and had a great reputation in the area. I should have stayed with my original design. I have a frost wall then an insulated pad on the house ... not one crack in 2400 sq ft after 7 years.


But it is there and it is what I need to use.



Lots of cracks ... but it has not moved since I have a ton of re-bar in it.


Maybe good that there is no tubes in it ... like I said, lots of cracks ... an not one where we made the cuts!
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Old 02-02-2020, 02:49 PM   #12
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Re: boiler vs hot air ... confused


Might want to look into a commercial boiler, to do the quick recovery you want to do.


https://www.lochinvar.com/products/c...e-tube-boiler/
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Old 02-02-2020, 03:05 PM   #13
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Re: boiler vs hot air ... confused


I think the problem here is that if I am talking $2K for the unit from HD then this unit will be $$$$$$$$$$


This is only a workshop and my budget is limited. The only reason I could afford the house and shop is because I do all my own work ... and then it took 7 years to build the house.


If I am talking large dollars for a boiler then I may as well go with a cheap furnace.


For example ... Alpine has a Bueridge or a Goodman ... 100,000 for about $1200 ... get two of these ... add in a few thousand for duct (I already have a 2" NG line run from the house to the shop) and $1000 for a tankless water heater ... probably in for $5k ... maybe $6K


Just want my the best "bag for the buck" ...



Thanks .... Mike
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Old 02-02-2020, 03:05 PM   #14
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Re: boiler vs hot air ... confused


Quote:
Originally Posted by xtal_01 View Post
Way too many ideas!
Oh, so you are looking for more ideas.......

.
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Old 02-02-2020, 03:19 PM   #15
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Re: boiler vs hot air ... confused


Quote:
Originally Posted by SPS-1 View Post
Oh, so you are looking for more ideas.......

.



LOL, he's worried about clogging up an air filter or heat exchanger in a gas furnace or unit heater. But not worried about clogging up any of the small holes in the ceramic burners.
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