Bypass design ideas

I live in New Mexico at 9300 feet elevation. In the fall the early mornings are pretty chilly but the days often warm up nicely. I am about to construct my first RMH and am wanting to install a bypass in my system so that I can light a quick fire in the morning and not overheat the house all day. My exit pipe will will come up very close to the bell. Is it better to install the bypass in the ducting inside the mass or would it be ok to come out the side of the top of the bell and tee directly into the exit pipe? Any thoughts and or design ideas/pictures/drawings would be very appreciated! Thanks in advance!

With your situation, the option of a quick fire that does not heat the mass sounds good. What you would want is a bypass from near the bottom of the barrel to the chimney, so that the whole barrel gets hot. Exiting from the top of the barrel would leave much of it cold. The high bypass idea is strictly for difficult starting situations.

A bypass inside the mass from near the barrel straight to the chimney connection would also work fine, if your layout makes that easy.

For my build, I'll weld up a sliding damper. Concept sketch attached. Will use same design for closing off the mass to the chimney. In the latter case, I believe the advantage over a rotating damper is that it will not form an obstruction for sweeping the chimney / the damper is not constantly in the flue gas flow.
Never welded so will see how it works out. This design could just be bolted as well, but as Peter has mentioned, you have to avoid your bypass being the weak link in your system (it's the only internal mechanical part).
I will be using thick (3-4mm) plates.

Glenn Herbert wrote:With your situation, the option of a quick fire that does not heat the mass sounds good. What you would want is a bypass from near the bottom of the barrel to the chimney, so that the whole barrel gets hot. Exiting from the top of the barrel would leave much of it cold. The high bypass idea is strictly for difficult starting situations.

A bypass inside the mass from near the barrel straight to the chimney connection would also work fine, if your layout makes that easy.

Glenn, if I put the bypass at the bottom of the barrel with a damper in it, would I still need a damper in the pipe where it enters the mass after exiting the manifold?

No, the usefulness of a bypass is that it gives a lower-friction path. A bit of air might still go through the bench, but it would be negligible, especially if the bench is cold.

People have tried multiple-duct routing, and reportedly found that even if you try to make them identical, one path will hog much of the flow. A bypass compared to a whole bench run will be no contest.

Glenn Herbert wrote:No, the usefulness of a bypass is that it gives a lower-friction path. A bit of air might still go through the bench, but it would be negligible, especially if the bench is cold.

People have tried multiple-duct routing, and reportedly found that even if you try to make them identical, one path will hog much of the flow. A bypass compared to a whole bench run will be no contest.

Ok. Thank you for the help. I have another question. I was about to start building my firebox and heat riser with clay slip. I just checked the weather and we are supposed to have freezing temperatures starting tonight. Will it cause a problem if that clay slip sealing off the firebrick isn’t completely dry and it freezes?

Freezing would compromise damp clay. If it is just at night, I would simply put a couple old blankets or whatever you have over it. A light bulb or the equivalent under the blankets would help.

I merged your stuff with the following thread. I hope that is okay by you.

I am wanting to start erecting my firebrick “J” tube using clay slip as sealer/mortar. Freezing temps are expected overnight for the next few nights. Will this have a negative affect on the clay slip? Do I need to try to keep it from reaching freezing temps in my little cabin?
Never worked with clay slip so any help would be appreciated!

Salem,

Any mortar that is water based and allowed to freeze when wet will have structure damaged and microscopic bonds between the mortar and the material cracked and weakened to the extent depending on freeze penetration depth and time.
I would suggest the following:
-add 10 % portland cement to accelerate drying
or/and
-preheat the bricks in some fire pit - they will hold enough heat to prevent any freeze damage
On top of that you can cover entire structure with a blanket.

When I was building a brick vault in my barn and temperatures were below freezing at night, I filled 5 gal buckets with hot water and put under the structure and also covered the vault with blankets on the outside.

I've just been convinced to add a bypass to the 8" RMH that I'll start building soon. I'm thinking about using a damper because they're easy to source and incorporate.

I don't like that dampers are 20% open even when closed. I see that Julian in this thread is going the custom welded route, for a much better product. Can anyone recommend a compromise  between the easily sourced, flimsy, leaky damper and the custom welded option?

Thanks in advance.

Hi Nick;
Check out how I modified a cast damper to use on Shorty Core.
https://permies.com/t/267527/Shorty-Core-bell

I see that McMaster Carr can sell and ship me a stainless steel guillotine aka blast gate. The price is almost $500, which is much more than I want to pay. It looks to be exactly the thing I was hoping to find though.

Thanks Thomas! I love that solution. I'll give it a try. Thanks for sharing.

Yes, blast gates work well.
I never saw a stainless one; they're sure a bit overpriced...
I previously used aluminum and steel blast gates. ( much cheaper)
There are concerns that the temperature may be too high for Aluminum at the top of a first-generation batch box.
Installing it a bit lower in the bell will alleviate those concerns.

From now on, I'll be using cast iron dampers & superwool on my builds, and recommending them to my customers.

Bypass gates are easy to build if you have the material and know what you want in the end. I would always make them removable ( i.e. slide in from the outside of the stove)  The internal pipe does not need to be any larger than the hole, and that hole just near the top of your bell.

With your properly built stove, super wool can be used for the gasket seal around the bypass.

This post shows mine that I built a few years back and it has never failed  And always did the trick.

https://permies.com/p/2256630    If that don't work, you can just go to the complete build tag at the bottom of this and work your way down, as there is a complete posting on just the bypass gate. ( all stainless)

Keep the home fires burning.

Scott Weinberg

I made a 4" stainless steel blast gate from scrap material from a discarded barbecue grill. It was light (26 ga +-) and easy to work with portable tools. I cut with tin snips, bent to a sleeve that the gate slides in, drilled out the rough circle in the sleeve and filed to a smooth circle. The whole thing was mortared into place, making sure the slide continued to operate.