Furnace came with house, need advice

[KentuckyHoosier]

I purchased a new house this year and it came with reversible split AC units (heat pumps) and an outside forced air wood furnace. Seemed good enough when I bought the house but I have very little experience with wood heat and none with furnaces. I got the dreaded (I did some reading, people really don’t care for these things) Hot Blast 1400, wood only I believe, and with winter here am trying to keep my split ac units from over working when it’s below 40f. It is in a shed outside and 5 or 6 feet from my house. It is plumbed through 6” fiberglass insulated piping. It is not permanent but it will need to get me a winter or two before I can get it replaced. I replaced the thermodisc and wired it correctly, cleaned the firebox, put in new bricks and replaced some rotten chimney pipe; so far I have a few descent nights of heat with it although it’s usually out before I wake up. I haven’t repaired the bimetal spring type dampener on the door yet but have it propped open enough to make it work. I have a few questions regarding this unit and my use of it. Is this furnace dangerous, if so what can be done to minimize it’s risk? How inefficient is it when compared to a better unit? What can I do (modifications or precautions) to make this furnace safer and increase efficiency? Does anybody have anything good to say about Hot Blast furnaces lol? I have absolutely nothing invested in this thing except to save my ac units from being overworked and keep my family warm until I can get a better replacement.
Thanks in advance,
KentuckyHoosier

 

[maple1]

What exactly do you have for heat pumps?

Hotblasts are marginal at best. Put one outdoors and its, well, worse.

 

[brenndatomu]

It is plumbed through 6” fiberglass insulated piping.

That's not nearly big enough...you need probably more along the lines of 12".
A 6" pipe has about 27 sq in. of area...the 12" is more like 112 sq in...and how much it can flow is an even more dramatic difference than that. 75 CFM vs 480!
Also, that flex pipe stuff with the fiberglass insulation is not rated nearly high enough for wood furnace duty...most of it is rated in the low 200's for max temp...a wood furnace will get there in a heartbeat if the fan quits for some reason (power out)
The best thing you can do is to make sure the supply line runs uphill the whole way so it can gravity flow if the blower quits.
It would be safer having this thing inside than being outside with a cobbled up mess for an install. Outside hot air furnaces were a bad idea...using a Hotblast, even worse.
I'd fix that bi-metallic spring sooner than later...but those aren't know for their reliability either.

 

[KentuckyHoosier]

It is not flex pipe but the big (10” outside diameter 6” inside diameter) double walled fiberglass filled stainless piping; it T’s into one pipe above the unit before leaving the shed and going into the house. There are 2 blowers on the back of the unit and it does make an uphill path to get into the house. When the blowers are off it does still move air into the house.
I have two outside Mitsubishi reversible split air conditioner units hooked into 4 wall units (2 per outside unit, half their capacity per outside unit). They keep the 1800sqft cape cod house toasty down to 40f (they still keep the house from being cold beyond that but they run very hard to do so) and very cool in the summer. It was still in the 90’s when we were doing viewings and inspections and the outside units were barely running. My outside walls are 2x8’s and the home inspector said he had never seen a house insulated as well as mine. With the furnace running the wall units do not come on and the house stays warmer than the thermostats for the house are set to (68f) down into the 20’s. My home was built in 2007 with no central air or heat and consequently no ducting. The Mitsubishi split A/C units were added by the second owners in 2015. No central ducting so each room has its own wall unit and thermostat remote control. Included are some relevant pictures to both responses.

 

[Fred61]

Cold climate heat pumps will be efficient down to 10. You must have older units. If they are cold climate inverter type you will not be over working them.

 

[maple1]

If they put in A/C only units, that's a darn shame. If not, they are able to heat your house easily at those temperatures and much colder.

 

[Fred61]

I get it that they are heat pumps from the original post. If they are inverter units, understand that the compressor unit will run almost constantly because they modulate as opposed to start/stop units from the past. That's where the efficiency comes from. Doesn't mean they are "overworked".

 

[maple1]

Heat pump model numbers should help explain.