Looking for shop heater advice (in WI)

[Tizzy]

I just removed my old outdoor wood burner system. I’m researching propane hanging units (separated combustion). I know and understand about short cycling but in my case there is no way to avoid it.
Shop details: 32x40x12 on 5” cement slab with frost walls, r-19 walls, r-38 ceiling, a few smaller windows and two 10x12 industrial overhead doors (I’ll have to see what they are rated).
I’d like to keep it around 50f and 65-70 when occupied.
Looking for suggestions on brand. I also want to use a concentric pipe of some kind. Price isn’t a huge factor. Is there a way to deal with condensate in the unit?
The ability for me to acquire parts and support after the sale is important. I’m installing myself.
Any advice on brand, size, what pipe options are available?
Thx

 

[spudley]

Why is there no way to avoid short cycling?

 

[Tizzy]

It’s my understanding from reading most posts regarding shop heaters that don’t run almost constantly, they are short cycling. I’d like a heater that I can set to keep the shop at 45-50 but also have a quick recover time when it’s occupied and set at 65-70 while throwing heat 35-40’.

 

[Bert_]

Maybe the point of heater sizing has been pushed to much. But it is hard to get the point across otherwise.

You just don't want a heater that only runs 5 minutes at a time. Longer run times are better for the heater and you.

 

[Tizzy]

I can understand and appreciate why it would need to run longer. Would setting the differential higher on the thermostat help with that? So, the issue is condensation, correct?

 

[Tizzy]

I’m looking at the Sterling GG75 with the sep combustion kit or the Modine HDS75. Does a stainless exchanger provide better longevity over aluminized? Also, the sterling offers a two stage gas valve. Would that be a benefit for an extremely well insulated shop or is that more of a greenhouse thing?

 

[TwoToque]

Well a stainless steel heat exchanger is supposed to last longer than aluminized which is why you pay more for it. It is not always a guarentee. Things that kill exchangers are condensation during off cycles at any time of the year and also over firing the burner. This last one will kill pretty fast sometimes. In regards to a two stage gas valve this means the unit will fire on low fire and is usually a snap action inside the valve. You have to set the low fire gas pressure to the manufacturers specs but is typically half of high fire for quick reference. The second action is a modulating diaphragm and will burn maximum BTU's after you set the high fire. I think propane is 11" w.c. if I recall and you also have to factor your elevation in Wisconson if you are above 2000 ft. I like a two stage valve better because it allows higher efficiency in the sense of burning half the BTU's on warmer winter days where you are only having to take the edge off. I want to say I think you will need a two stage thermostat W1 and W2 so that after a built in time in the tstat on first stage then second stage W2 will power the high fire terminal if the desired setpoint has not been made yet. The installation manual will explain this and what tstat is needed in case I am wrong there.

 

[Alexto1]

good

 

[Showkey]

I can understand and appreciate why it would need to run longer. Would setting the differential higher on the thermostat help with that? So, the issue is condensation, correct?

Yes.......if you can find an adjustable differential, also one with an adjustable *anticipator.

75k for 1200sqft your not that far off of ideal.............that has discussed dozens of times.
Condensation is two fold......short run time and cold intake air temperatures ( below 50*)
Avoid those two issues and there should be no real issues for 20years. Your well insulated so your pretty much the typical shop heater situation.

If considering a Condensing unit you must deal with the water to a drain. There will be “a lot” of water “about “ a gallon of water for every gallon of propane used. Drain to outside day light would be a problem in winter.
Most ceiling hanging heaters are NOT condensing units. Condensing units are PVC venting 90plus efficiency.
If I was considering a new shop heater I would consider a 45-60k gas 92- 96% high efficiency furnace. $900-$1200 for the unit delivered.
Mounted high, vented with PVC, condensate drain, sealed combustion, outside air intake etc

https://www.alpinehomeair.com/viewcategory.cfm?categoryID=128&page=1


One advantage of condensing units they are stainless.
Disadvantage dealing with the condensate and they should never freeze.




* A heat anticipator is an electrical resistor device mounted in the center of many mechanical thermostats. It fine tunes the point at which the thermostat turns off the furnace burners. ... The heat anticipator essentially consists of a small disc attached to the bimetallic coil of the thermostat

 

[Bert_]

I can understand and appreciate why it would need to run longer. Would setting the differential higher on the thermostat help with that? So, the issue is condensation, correct?

Seems like many newer electronic thermostats are bad about trying to maintain temperature to less than 1 degree difference. On a lot of them the differential can't be changed. That's a bad combination with an over-sized furnace.

I had a programmable Honeywell thermostat in my house and the furnace is admittedly pretty oversized (I didn't put it in). At first the thermostat would have the furnace trying to run at least five times an hour. With some fiddling I was able to get it down to two or three times an hour but that still meant short cycles for the furnace.

I finally swapped it out for a mercury thermostat. The temperature swings aren't really any more noticeable but the furnace never runs more than once an hour. In mild weather it might go two hours. Since the off time is longer the runtime is also much longer and that's a lot better for the furnace.