Windy days and cold nights

[Wood-row Wilson]

I've owned and have been running my Garn Jr. for over a year now, and I've been very pleased, but I find on windy days or single-digit nights, I can't seem to stay up to the thermostat set temp. It's been mildly windy and lows in the teens here in west Michigan lately, and like a handful of times since starting with my new heat source, I'm findings nights or even days that the furnace simply will not keep up! That has been the case the last couple of days (windy & cold), and the house temperature starts to rise as I get the water back up to 160 degrees+. Thermostat is set to 68 and at temp when I start a small, final fire at 12:30pm. Woke up the following morning (6:00am) and it was 64 in the house. What's interesting is that my tank temp was still at 140, but somehow not able to catch up or keep up with the fan continuing to blow!

Perhaps it's as simple as a bigger pump? Maybe I need to address some insulation issues...? A bigger coil in the furnace plenum? Taking all considerations at this point. Thankfully, if tended to by keeping the tank temp high, I'm able to combat the issues...but something has to give, right? Thanks all!

Hopefully the information below of my setup below is helpful...

Lines: 1"
Heat loss through lines: Very minimal to non-existent
Pump: Badger 20 GPM 3 speed, set at highest speed
Other uses: DHW, separate deliver and return lines from furnace
House: 2,000sq.
Garn: In pole barn, well insulated, steel stud and drywall

 

[mike van]

A few things that happened to me in the process of learning the Garn - The first was air in my oil boiler [that the Garn flows through] Second was my heat exchanger right behind the Garn, was mostly plugged, third, at the start of this season was the y-strainer on the Garn side, plugged with soft gooey white matter that I now believe was the anode disintegrating. My setup has about 240 ft [supply & return] of 1 1/4 copper, well insulated too, with a Gundfoss pump # ups 15-58 fc pump on it, 3 speed set on medium. I don't know what that gives for a flow rate? Forgot to add - Just my 2 cents, and i'm no boiler expert, but 20 gpm sounds like a lot of flow, maybe it's blowing the water through faster than it can be heated? Try it on medium maybe?

 

[maple1]

That is a lot of flow - I'd hazard a guess at too much. 20gpm at a 20° dT is almost 200,000 btu/hr. HUGE.

I would double check all the things mike van said re. dirt related stuff - particularly the anode rod thing.

I would also measure pipe temps in & out of your furnace coil.

If all is well with respect to the rest of the system, I would go bigger in the coil. But we don't know what you have now, either.

 

[stee6043]

Based on my own experience I'd expect my furnace fan to run almost non-stop on a "rather cold" day like we've been having this week if my tank temps were at 140. For most run-of-the-mill heat exchangers you're going to find 140 is about the lowest you can go on supply temp on an average heating day. On a "rather cold" day I'm not surprised you're losing ground on the house temp. Mine would be doing the same.

A higher dollar coil in your furnace would definitely help. So would low temp emitters throughout the house. Both of these cost money, however. I combated this issue by making sure I didn't let my tank temps get that low. If needed during a cold snap I'd get up in the middle of the night to toss in a load, or set my timer such that I could toss a load in before work in the morning without a full blown restart. Most days, however, this should not be needed.

And as others have stated, slow that pump down! It'll help reduce mixing in your tank at the very least...

 

[maple1]

It'll help reduce mixing in your tank at the very least...

Likely a very large factor here. Stratification will help get the most mileage from storage. Pumping that much flow will get the least.

I think I have read though that something else about Garns is also 'contra-stratification'? Or maybe that was when burning/charging. No Garn experience, so getting a bit over my head here....

 

[Tennman]

Does "coil in furnace plenum" mean you're using a water to air HX with forced air? If so do you know your water temp into and out of the HX and blower CFM? Our WTA HX was sized based on CFM, gpm, and temp drop at a mean water in temp. Our HX vendor nailed it.

 

[Wood-row Wilson]

It'll help reduce mixing in your tank at the very least...

Likely a very large factor here. Stratification will help get the most mileage from storage. Pumping that much flow will get the least.

Thank all for the replies/confirmations on flow speed. I'll change to medium, but it's warming up a bit here so I may not find more until the middle of next week

Does "coil in furnace plenum" mean you're using a water to air HX with forced air? If so do you know your water temp into and out of the HX and blower CFM? Our WTA HX was sized based on CFM, gpm, and temp drop at a mean water in temp. Our HX vendor nailed it.

Yes, water to air HX with forced air, @Tennman ... having a tough time tracking the acronyms, thought...CFM? WTA?

 

[maple1]

CFM = cubic feet per minute.

If you don't measure some things to get a handle on what is going on, you are kind of guessing at things. First thing to measure is water temps in & out of the coil. But if your coil is undersized, you'd be behind the 8 ball right off. Make sure to check ALL the things mike van pointed out. And there is a thread on here about the anode rods in Garns - seemed like very important reading for Garn owners.

And, WTA = Water-To-Air.