Can I test my garage heater before installing?

[HotRodHudson]

I’m excited to say we are finally getting out of the negative temperatures over the next few days. Thus I figured it was a good time to finally install a new 75k btu Hamilton brand garage heater but I need advice on possibly test running it 1st.

I’ve been dragging this “new in the box” furnace around for more years than I care to admit but let’s just say this is house #3... Anyway here’s the situation; I have around a 5 car space (3 car plus shop behind it) in an L shape which is open & 11 ft ceilings. There already is a small gas heater in place, approximately 30k btu which is really undersized for the space, thus the “new” one at 75 btu would be perfect. I have already checked the vent pipe & supply line and both more than meet the needed requirements for this new furnace. So other than mounting it & making the connections, everything looks to be in order for a straightforward swap.

Since this garage heater has been around for so long & exposed to high humidity & possibly some water dripping being stored in a barn for a period of time, I would like to test run it 1st. Since I don’t have a lift or a way to raise it up to install it & test it in place could I connect it to the outside bbq natural gas line from my house? Obviously needing power & thermostat connection too but what other issues may I run into and is it feasible to do this?

 

[dave67fd]

I would remove the units covers and fully inspect (including burner tubes) for any moisture corrosion. If it looks good I would just properly install and run. Assuming the unit is already set up for NG? If your not fully up to doing a proper install have a pro do it for you. Check your state and local codes as well. I would only pretest if i was 200% sure all is safe prior to firing.

 

[D45]

Should be an easy swap!!

The 75k will obviousmy be a tad larger, so you might need a longer vertical section

I just swapped out a 45k for a 75k, and it was fast

 

[Matt Matt]

With a quick visual inspection I don’t see why you cannot benchtest it.
But, I don’t think your barbeque line will provide enough flow. Most barbeques are typically around half inch feedline. And depending on the length of the run there could be a lot of static pressure. What size pipe do you have feeding the garage? And have you done a load calculation for that branch and for the whole system? When I added 30,000 BTU heater to my garage shop, I had to bring in a bigger main trunk. You’ll probably need a three-quarter inch pipe feeding the garage. What size is your main pipe trunk?

If you’re pretty sure you can just hook it up go for. Here’s a pretty dry video if you’d like to do load calculation.

 

[HotRodHudson]

I opened the furnace panels up & cleaned it up. I didn’t find any rust, signs of water or any issues. I was pleasantly surprised how good it looked. After another going over the installation manual & a quick call I found out it’s actually a Modine Hot Dog 75 btu that Hamilton sold without the stickers, bonus! The only things I need to change is to move the furnace another 6” away from the vertical vent tube so I’ll move the unistruts & rod then I need to change the location of the shut off for easier removal if needed in the future.

There’s definitely enough gas supply, 1 inch then 12 ft of 1/2” to the heater. There was a gas dryer connection in the house which we no longer use so I feel confident I have good pressure & the calculations work out good too. I’ve got a couple days where highs will be in the 30’s so I’m going to just pull the old one & install this one. I think the swap will go well & after opening up the heater I’m feeling good about it too. Thanks guys!

 

[D45]

You might want to look into my thread, about the HD 75K tripping the top flame rollout sensor:

https://www.garagejournal.com/forum/showthread.php?t=374715

Now would be the perfect time to pinch and seal up the top burner, before you install it